Introduction to Computer Networking Guy Leduc Chapter 6leduc/cours/IRI/IRI-ch6.pdf · · 2017-12-0611 © From Computer Networking, by Kurose&Ross DataLink Layer 6-21 Multiple Access

1

copy From Computer Networking by KuroseampRoss DataLink Layer 6-1

Introduction to Computer Networking

Guy Leduc

Chapter 6 Link Layer and LANs Computer Networking

A Top Down Approach 7th edition Jim Kurose Keith Ross Addison-Wesley April 2016


Chapter 6 The Data Link Layer Our goals   understand principles behind data link layer

services   error detection   sharing a broadcast channel multiple access   link layer addressing   local area networks Ethernet

  instantiation and implementation of various link layer technologies

2


Link Layer

  61 Introduction and services

  62 Error detection   63 Multiple access

protocols   64 LANs

  Addressing ARP   Ethernet   Switches

  65 Data center networking

  66 A day in the life of a web request


Link Layer Introduction Some terminology   hosts and routers are nodes

  = devices with a network layer (L3)   communication channels that

connect adjacent nodes along communication path are links   wired links   wireless links   LANs

  layer-2 packet is a frame encapsulates datagram

data-link layer has responsibility of transferring datagram from one node to physically adjacent node over a link

global ISP

3


Link layer context   datagram transferred by

different link protocols over different links   eg Ethernet on first link

MPLS on intermediate links WiFi on last link

  each link protocol provides different services   eg may or may not

provide reliable data transfer (rdt) over link

transportation analogy   trip from Princeton to

Lausanne   limo Princeton to JFK   plane JFK to Geneva   train Geneva to Lausanne

  tourist = datagram   transport segment =

communication link   transportation mode = link

layer protocol   travel agent = routing

algorithm


Link Layer Services   framing link access

  encapsulate datagram into frame adding header trailer   channel access if shared medium   ldquoMACrdquo addresses used in frame headers to identify sending

receiving node interfaces bull  different from IP addresses (which identify source dest

host interfaces)   reliable delivery between adjacent nodes

  we learned how to do this already (chapter 3)   seldom used on low bit-error link (fiber some twisted pair)   wireless links high error rates

bull  Q why both link-level and end-end reliability

4


Link Layer Services (more)

  flow control   pacing between adjacent sending and receiving nodes

  error detection   errors caused by signal attenuation noise   receiver detects presence of errors

bull  signals sender for retransmission or drops frame

  error correction   receiver identifies and corrects bit error(s) without resorting

to retransmission   half-duplex and full-duplex

  with half duplex nodes at both ends of link can transmit but not at same time


Where is the link layer implemented   in each and every host   link layer implemented in

ldquoadaptorrdquo (aka network interface card NIC) or on a chip   Ethernet card 80211 card

Ethernet chipset   implements link physical

layer   attaches into hostrsquos system

buses   combination of hardware

software firmware

controller

physical transmission

cpu memory

host bus (eg PCI)

network adapter card

application transport network

link

link physical

5


Adaptors communicating

  sending side   encapsulates datagram in

frame   adds error checking bits   (rdt flow control etc)

  receiving side   looks for errors   (rdt flow control etc)   extracts datagram passes

to upper layer at receiving side

controller controller

sending host receiving host

datagram datagram

datagram

frame


Link Layer




  addressing ARP   Ethernet   switches



6


Error Detection EDC= Error Detection (and sometimes Correction) bits (redundancy) D = Data protected by error checking may include header fields

bull  Error detection not 100 reliable bull  protocol may miss some errors (why) but rarely bull  larger EDC field yields better detection (and correction)

otherwise

EDC = f (D) for some function f

Is EDCrsquo = f (Drsquo)


Parity Checking Single Bit Parity Detect single bit errors

Two Dimensional Bit Parity Detect and correct single bit errors

0 0

7


Internet checksum (review)

Sender   treat segment contents as

sequence of 16-bit integers

  checksum addition (1rsquos complement sum) of segment contents

  sender puts checksum value into UDPTCP checksum field

Receiver   compute checksum of

received segment   check if computed checksum

equals checksum field value   NO - error detected   YES - no error detected

But maybe errors nonethelesshellip

Goal detect ldquoerrorsrdquo (eg flipped bits) in transmitted packet (note used at transport layer only)


Cyclic Redundancy Check (CRC)   more powerful error-detection coding   view data bits D as a binary number   choose r+1 bit pattern (generator) G   goal choose r CRC bits R such that

  ltDRgt exactly divisible by G (in base-2 arithmetic)   receiver knows G divides ltDRgt by G

if non-zero remainder error detected   can detect any single error burst not longer than r bits (see later)

  widely used in practice (Ethernet 80211 WiFi ATM)

ltDRgt =

=

8


CRC Example Want

D2r XOR R = nG equivalently

D2r = nG XOR R equivalently if we divide D2r by G

(in base-2 arithmetic) want remainder R

or R = D2r mod G

euro

R = remainder D sdot 2r

G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend

In base-2 arithmetic no carries no borrows 1 + 1 = 0 0 ndash 1 = 1 + - XOR all equivalent

10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder


CRC Example the polynomial view

Transmitted frame T(x) = D(x) xr - R(x)

Is divisible by G(x)

D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro

R(x) = remainder D(x) sdot xr

G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9


Why does it work   We have T(x) = D(x) xr - R(x)

  By construction T(x) is divisible by G(x) bull  T(x) mod G(x) = 0

  This is easy to check at the receiver provided that the sender and the receiver agree on a certain G(x)

  Suppose some errors occur during transmission   The received frame is T(x) + E(x)   The receiver will then calculate the remainder of

(T(x) + E(x)) G(x)   This remainder is equal to the remainder of E(x) G(x)

bull  (T(x) + E(x)) mod G(x) = E(x) mod G(x)   If the error is an E(x) that is not divisible by G(x) it will

be detected   The choice of G(x) is thus very important

  But impossible to detect all errors Why

From Computer Networks by Tanenbaum copy Prentice Hall


Example of CRC with properties (1)   Example of Generator G(x) = x16 + x12 + x5 + 1   Property 1

G(x) detects every error consisting of an odd number of error bits Proof   G(x) is divisible by (x + 1) in other words G(x) = (x + 1) H(x)

bull  in base-2 arithmetic G(1) = 1+1+1+1 = 0   An odd number of bit errors is modelled by a polynomial E(x) with an odd

number of terms   Such E(x) cannot be divisible by (x + 1)

bull  in base-2 arithmetic E(1) = 1 for such E(x)   Therefore E(x) is not divisible by G(x)

  More generally a G(x) composed of an even number of terms detects every error consisting of an odd number of error bits   At least as good as a parity bit   Could a parity bit be seen as a trivial CRC Any G(x) to suggest

  Property 2 G(x) detects every 2-bit error (in any place in the frame)


10


Example of CRC with properties (2)   G(x) = x16 + x12 + x5 + 1   Property 3 G(x) detects every single error burst of length le 16 bits

  An error burst of length n (ge 2) is 1 error bit followed by n-2 bits (correct or not) followed by 1 error bit

Proof   An error burst of length le 16 bits can be modelled by E(x) = H(x) xk

with H(x) of degree le 15 and k (ge 0) being the number of bits after the last error bit

  H(x) is not divisible by G(x) because H(x) is of degree le 15 and G(x) of degree 16

  Using G(0) ne 0 it is easy to prove by induction that if H(x) xk is not divisible by G(x) which is true for k=0 then H(x) xk+1 is not divisible by G(x) This leads to E(x) not being divisible by G(x)

  More generally a G(x) of degree r with G(0) ne 0 detects every single error burst of length le r bits

  If errors are random G(x) detects   99997 of the 17-bit error bursts (Any undetectable error burst to suggest)   99998 of the 18-bit error bursts



Link Layer







11


Multiple Access Links and Protocols Two types of ldquolinksrdquo   point-to-point

  PPP for dial-up access   point-to-point link between Ethernet switch and host

  broadcast (shared wire or medium)   old-fashioned Ethernet   upstream Hybrid Fiber Coax (HFC)   80211 wireless LAN

shared wire (eg cabled Ethernet)

shared RF (eg 80211 WiFi)

shared RF (satellite)

humans at a cocktail party

(shared air acoustical)


Multiple Access protocols   single shared broadcast channel   two or more simultaneous transmissions by nodes

interference   collision if node receives two or more signals at the same time

multiple access protocol   distributed algorithm that determines how nodes

share channel ie determine when node can transmit   communication about channel sharing must use channel

itself   no out-of-band channel for coordination

12


An Ideal Multiple Access Protocol

Given broadcast channel of rate R bps

Desiderata 1 when one node wants to transmit it can send at

rate R 2 when M nodes want to transmit each can send at

average rate RM (fairness) 3 fully decentralized

  no special node to coordinate transmissions   no synchronization of clocks slots

4 simple


MAC Protocols a taxonomy Three broad classes   Channel Partitioning

  divide channel into smaller ldquopiecesrdquo (time slots frequency code)

  allocate piece to node for exclusive use   Random Access

  channel not divided allow collisions   ldquorecoverrdquo from collisions

  ldquoTaking turnsrdquo   nodes take turns but nodes with more to send can take

longer turns

13


Channel Partitioning MAC protocols TDMA TDMA time division multiple access   access to channel in rounds   each station gets fixed length slot (length =

packet transmission time) in each round   unused slots go idle   example 6-station LAN 134 have packet slots

256 idle

1 3 4 1 3 4

6-slot frame


Channel Partitioning MAC protocols FDMA FDMA frequency division multiple access   channel spectrum divided into frequency bands   each station assigned fixed frequency band   unused transmission time in frequency bands go idle   example 6-station LAN 134 have packet frequency

bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14


Random Access Protocols

  When node has packet to send   transmit at full channel data rate R   no a priori coordination among nodes

  two or more transmitting nodes ldquocollisionrdquo   random access MAC protocol specifies

  how to detect collisions   how to recover from collisions (eg via delayed

retransmissions)   Examples of random access MAC protocols

  slotted ALOHA   ALOHA   CSMA CSMACD CSMACA


Slotted ALOHA

Assumptions   all frames have same

size   time is divided into

equal size slots (time to transmit 1 frame)

  nodes start to transmit only at slot beginning

  nodes are synchronized   if 2 or more nodes

transmit in slot all nodes detect collision

Operation   when node obtains fresh

frame transmits in next slot   if no collision node can

send new frame in next slot

  if collision node retransmits frame in each subsequent slot with probability p until success

15


Slotted ALOHA

Pros   single active node can

continuously transmit at full rate of channel

  highly decentralized only slots in nodes need to be in sync

  simple

Cons   collisions wasting slots   idle slots   nodes may be able to

detect collision in less than time to transmit packet

  clock synchronization

1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E


Slotted Aloha efficiency

  Suppose N nodes with many frames to send each transmits in slot with probability p   Note not exactly slotted ALOHA

  prob that node 1 has success in a slot = p(1-p)N-1

  prob that any node has a success = Np(1-p)N-1

  For max efficiency with N nodes find p that maximizes Np(1-p)N-1

  p = 1N   For many nodes take limit of

Np(1-p)N-1 = (1-1N)N-1

as N goes to infinity it gives a max efficiency of 1e = 037

Efficiency is the long-run fraction of successful slots when there are many nodes each with many frames to send

At best channel used for useful transmissions 37 of time

euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16


Pure (unslotted) ALOHA   unslotted Aloha simpler no synchronization   when frame first arrives

  transmit immediately   collision probability increases

  frame sent at t0 collides with other frames sent in [t0-1t0+1]

In frame time units


Pure Aloha efficiency P(success by given node) = P(node transmits) P(no other node transmits in [t0-1t0] P(no other node transmits in [t0t0+1] = p (1-p)N-1 (1-p)N-1

= p (1-p)2(N-1)

P (success by any node) = Np (1-p)2(N-1)

hellip choosing optimum p and then letting N go to infinity

= 1(2e) = 018

Even worse than slotted Aloha

17


Efficiency wrt average traffic load   Let G = pN be the average aggregated traffic load

(or demand) per frame time   = nr of transmission attempts per frame time   N stations sending one frame with probability p in every

frame time   Efficiency

  Slotted ALOHA Np(1-p)N-1 = G (1-GN)N-1   ALOHA Np(1-p)2(N-1) = G (1-GN)2(N-1)

  Efficiency (for a given G) when N gtgt   Slotted ALOHA G e-G

  ALOHA G e-2G

  If G ltlt 1 efficiency asymp G perfect

euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG


Efficiency Optimum out of 100 frame times- 37 are used effectively- 26 are collisions- 37 are just empty


ALOHA versus Slotted ALOHA

frame

Ideal S = G

18


CSMA (Carrier Sense Multiple Access)

Improving pure ALOHA with carrier sensing

CSMA listen before transmit If channel sensed idle transmit entire frame If channel sensed busy defer transmission

  LBT Listen Before Talking (and deference)

  human analogy donrsquot interrupt others


CSMA collisions collisions can still occur propagation delay means two nodes may not hear each otherrsquos transmission

collision entire packet transmission time wasted

spatial layout of nodes

distance amp propagation delay play role in determining collision probability

19


persistent CSMA (if channel is busy listen until it is freed)

non persistent CSMA (if channel is busy program a new attempt later)

p-persistent CSMA While true do

if channel is free then

with probability p immediate transmission or

with probability 1-p stay idle during at least propagation time (τ) else listen until the channel is freed

Trade-off between efficiency and delay bull This introduces a useless delay at low loads bull But the efficiency of the channel is better at high loads

p-persistent CSMA


Efficiency

Efficiency versus load for various random access protocols


frame

Ideal

20


B = Channel Data Rate (so-called Bandwidth) (bps) F = (Maximum) Frame size (bits) L = Length of the channel (m) c = Propagation speed (ms)

τ = Propagation delay = L c (s) T = Transmission delay = F B (s) τ contention period (risk of collision) After τ channel implicitly reserved during T-τ

Let a = τ T = BL cF Need small a Let a = 1 rarr F = 100 BL c = plusmn 5 10-7 BL (with c = plusmn 200000 kms) Let B = 10 Mbps L = 25 km rarr F = 12500 bits (= 15625 bytes) This is roughly the Ethernet frame size

Engineering a CSMA network


CSMACD (Collision Detection) CSMACD carrier sensing deferral as in CSMA

  collisions detected within short time   colliding transmissions aborted reducing channel

wastage   collision detection

  easy in wired LANs measure signal strengths compare transmitted received signals

  difficult in wireless LANs received signal strength overwhelmed by local transmission strength

  human analogy the polite conversationalist

21


CSMACD collision detection CSMACD CSMA

Lost time le 2 τ(worst case 2 max propagation times when the 2 stations are at the 2 ends) + detectabort time No abort so loss is T


  To detect collision the sender must still be transmitting when the collision propagates back to it So the condition is

T gt 2τ which means FB gt 2 Lc which leads to a minimal Fmin = 2BLc = plusmn BL 10-8 bits

  Let B = 10 Mbps L = 25 km rarr Fmin = plusmn 250 bits (= plusmn 32 bytes)   Ethernet has chosen 64 bytes = 512 bits (extra margin due to other delays)

A B

(a)

A B

(b)

A B

(c)

A B

(d)Collision attime τ

Noise burst getsback to A at 2τ

Packet startsat time 0

Packet almostat B at τ-ε

Minimal frame size with CSMACD


22


Ethernet CSMACD algorithm 1 NIC receives datagram from

network layer creates frame 2 If NIC senses channel idle

starts frame transmission If NIC senses channel busy waits until channel idle then transmits

3 If NIC transmits entire frame without detecting another transmission NIC is done with frame

4 If NIC detects another transmission while transmitting (collision) aborts and sends jam signal

5 After aborting NIC enters binary (exponential) backoff after mth collision (m le 10) for this frame NIC chooses K at random from 012hellip2m-1 NIC waits K512 bit times returns to Step 2 (for m gt 10 take K in 01023)

So longer backoff interval when more collisions for a given frame

With this backoff algorithm Ethernet is sort of p-persistent CSMA with an adaptive p after the 1st collision


S = T (T + α2τ) = 1 (1 + α2τT) = 1 (1 + α2BLcF ) For large N α converges towards e (plusmn27) for a p-persistent CSMA with p = 1N (ideal case)

So for N gtgt S cannot be better than 1 (1 + e2τT) = 1 (1 + 54 τT)

Number of active stations = N

Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames


Channel efficiency of an adaptive p-persistent CSMACD

Let α = the average number of slots (2 τ) before any successful transmission

Incr

easi

ng f

ram

e si

ze

23


ldquoTaking Turnsrdquo MAC protocols

channel partitioning MAC protocols   share channel efficiently and fairly at high load   inefficient at low load delay in channel access

1N bandwidth allocated even if only 1 active node

Random access MAC protocols   efficient at low load single node can fully

utilize channel   high load collision overhead

ldquotaking turnsrdquo protocols look for best of both worlds


ldquoTaking Turnsrdquo MAC protocols Polling   master node

ldquoinvitesrdquo slave nodes to transmit in turn

  typically used with ldquodumbrdquo slave devices

  concerns   polling overhead   latency   single point of

failure (master)

master

slaves

poll

data

data

24


ldquoTaking Turnsrdquo MAC protocols Token passing   control token passed from

one node to next sequentially

  token message   concerns

  token overhead   latency   single point of failure

(token)   known upper bound on

access time to channel o  ne CSMA

T

data

(nothing to send)

T


cable headend

CMTS

ISP

cable modem termination system

  multiple 40Mbps downstream (broadcast) channels   single CMTS transmits into channels

  multiple 30 Mbps upstream channels   multiple access all users contend for certain upstream

channel time slots (others assigned)

Cable access network

cable modem splitter

hellip

hellip

Internet framesTV channels control transmitted downstream at different frequencies

upstream Internet frames TV control transmitted upstream at different frequencies in time slots

25


DOCSIS Data Over Cable Service Interface Spec   FDM over upstream downstream frequency channels   TDM upstream some slots assigned some have contention

  downstream MAP frame assigns upstream slots   request for upstream slots (and data) transmitted

random access (binary backoff) in selected slots

MAP frame for Interval [t1 t2]

Residences with cable modems

Downstream channel i

Upstream channel j

t1 t2

Assigned minislots containing cable modem upstream data frames

Minislots containing minislots request frames

cable headend

CMTS



Summary of MAC protocols

  channel partitioning by time frequency (or code)   Time Division Frequency Division

  random access (dynamic)   ALOHA S-ALOHA CSMA CSMACD   carrier sensing easy in some technologies (wire) hard in

others (wireless)   CSMACD used in Ethernet   CSMACA used in 80211

  taking turns   polling from central site token passing   Bluetooth FDDI Token Ring

  Cable access networks use a combination of them

26


Link Layer



protocols   64 LAN





MAC Addresses and ARP  32-bit IP address

  network-layer address for interface   used for layer 3 (network layer) forwarding

 MAC (or LAN or physical or Ethernet) address   function used ldquolocallyrdquo to get frame from one

interface to another physically-connected interface (same network in IP-addressing sense)

 48-bit MAC address (for most LANs) bull  burned in NIC ROM also sometimes software settable bull  Eg 1A-2F-BB-76-09-AD

hexadecimal (base 16) notation (each ldquonumberrdquo represents 4 bits)

27


LAN addresses and ARP Each adapter on LAN has unique LAN address

adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN (wired or wireless)


LAN addresses (more)

  MAC address allocation administered by IEEE   manufacturer buys portion of MAC address space

(to assure uniqueness)   analogy

  MAC address like Social Security Number   IP address like postal address

  MAC flat address portability   can move LAN card from one LAN to another

  IP hierarchical address NOT portable   address depends on IP subnet to which node is attached

28


ARP Address Resolution Protocol

 ARP table each IP node (host router) on LAN has table   IPMAC address

mappings for some LAN nodes lt IP addr MAC addr TTLgt

  TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determine interfacersquos MAC address knowing its IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788


ARP protocol same LAN   A wants to send datagram

to B   Brsquos MAC address not in Arsquos

ARP table   A broadcasts ARP query

packet containing Bs IP address   dest MAC address =

FF-FF-FF-FF-FF-FF   all nodes on LAN

receive ARP query   B receives ARP packet

replies to A with its (Bs) MAC address   frame sent to Arsquos MAC

address (unicast)

  A caches (saves) Brsquos IP-to-MAC address pair in its ARP table until information becomes old (times out)   soft state information

that times out (goes away) unless refreshed

  All other stations had also cached Arsquos IP-to-MAC pair

  ARP is ldquoplug-and-playrdquo   nodes create their ARP

tables without intervention from net administrator

29


walkthrough send datagram from A to B via R   focus on addressing ndash at IP (datagram) and MAC layer (frame)   assume A knows Brsquos IP address   assume A knows IP address of first hop router R (how)   assume A knows Rrsquos MAC address (how)

Addressing routing to another LAN

R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B

This is a really important example ndash make sure you understand


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222

  A creates IP datagram with IP source A destination B   A creates link-layer frame with Rs MAC address as dest frame

contains A-to-B IP datagram MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B

30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

  frame sent from A to R

IP Eth Phy

  frame received at R datagram removed passed up to IP

MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B

IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222

  R forwards datagram with IP source A destination B   R creates link-layer frame with Bs MAC address as dest frame

contains A-to-B IP datagram

MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A

IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B

Addressing routing to another LAN   R forwards datagram with IP source A destination B   R creates link-layer frame with Bs MAC address as dest frame


IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer








Ethernet ldquodominantrdquo wired LAN technology   first widely used LAN technology   simple cheap   single chip multiple speeds (eg Broadcom BCM5761)   kept up with speed race 10 Mbps ndash 10 Gbps

Metcalfersquos Ethernet sketch

33


Ethernet physical topology   bus popular through mid 90s

  all nodes in same collision domain (can collide with each other)

  star prevails today   bus was replaced by central device

(initially hubs now switches)

hub or switch

bus coaxial cable

star


Hubs physical-layer (ldquodumbrdquo) repeaters

  bits coming in one link go out all other links at same rate

  all nodes connected to hub can collide with one another   no frame buffering at hub   no CSMACD at hub host NICs detect collisions

hub

34


Switches   switches prevail today

  active switch in center   each ldquospokerdquo runs a (separate) Ethernet protocol

(nodes do not collide with each other)   more later

switch


Ethernet Frame Structure Sending adapter encapsulates IP datagram (or other

network layer protocol packet) in Ethernet frame

Preamble   7 bytes with pattern 10101010 followed by one

byte with pattern 10101011   used to synchronize receiver sender clock rates

dest address

source address

data (payload) CRC preamble

type

35


Ethernet Frame Structure (more)   Addresses 6 byte source destination MAC

addresses   if adapter receives frame with matching destination

address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol

  otherwise adapter discards frame   Type indicates higher layer protocol (mostly IP

but others possible eg Novell IPX AppleTalk)   CRC cyclic redundancy check at receiver

  error detected frame is dropped

dest address

source address


type


Ethernet Unreliable connectionless

  connectionless No handshaking between sending and receiving NICs

  unreliable receiving NIC doesnrsquot send acks nor nacks to sending NIC   data in dropped frames recovered only if initial

sender uses higher layer rdt (eg TCP) otherwise dropped data lost

  Ethernetrsquos MAC protocol unslotted CSMACD with binary backoff

36


8023 Ethernet Standards Link amp Physical Layers

 many different Ethernet standards   common MAC protocol and frame format   different speeds 2 Mbps 10 Mbps 100 Mbps

1 Gbps 10 Gbps   different physical layer media fiber cable


link physical

MAC protocol and frame format

100BASE-TX

100BASE-T4

100BASE-FX 100BASE-T2

100BASE-SX 100BASE-BX

fiber physical layer copper (twisted pair) physical layer


Link Layer







37


Ethernet Switch   link-layer device smarter than hubs take

active role   store forward Ethernet frames   examine incoming framersquos MAC address selectively

forward frame to one-or-more outgoing links when frame is to be forwarded on segment uses CSMACD to access segment

  transparent   hosts are unaware of presence of switches

  plug-and-play self-learning   switches do not need to be configured


Switch multiple simultaneous transmissions

  hosts have dedicated direct connection to switch

  switches buffer packets   Ethernet protocol used on

each incoming link but no collisions full duplex   each link is its own collision

domain   switching A-to-Arsquo and

B-to-Brsquo can transmit simultaneously without collisions   not possible with dumb hub

switch with six interfaces (123456)

A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38


Switch forwarding table

Q how does switch know Arsquo reachable via interface 4 Brsquo reachable via interface 5


A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6   A each switch has a switch table each entry   (MAC address of hostrouter

interface to reach hostrouter time stamp)

  looks like a forwarding table

Q how are entries created maintained in switch table

  something like a routing protocol


A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

Switch self-learning   switch learns which hosts

routers can be reached through which interfaces   when frame received

switch ldquolearnsrdquo location of sender incoming LAN segment

  records senderlocation pair in switch table

A Arsquo

Source A Dest Arsquo

MAC addr interface TTL Switch table

(initially empty) A 1 60

39


Switch frame filteringforwarding When frame received at switch

1 record incoming link MAC address of sending hostrouter 2 index switch table using MAC destination address 3 if entry found for destination

then if dest on segment from which frame arrived

then drop the frame else forward the frame on interface indicated by entry else flood forward on all but the interface

on which the frame arrived


A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

Self-learning forwarding example A Arsquo


MAC addr interface TTL switch table


A Arsquo A Arsquo A Arsquo A Arsquo A Arsquo

  frame destination Arsquo location unknown

flood

Arsquo A

  destination A location known

Arsquo 4 60

selectively send on just one link

40


Interconnecting switches   switches can be connected together

  Q sending from A to F - how does S1 know how to forward frame destined for F via S4 and S2

  A self learning (works exactly the same as in single-switch case)

A

B

S1

C D

E

F S2

S4

S3

H I

G


Self-learning multi-switch example Suppose C sends frame to I I responds to C

  Q show switch tables and packet forwarding in S1 S2 S3 S4

A

B

S1

C D

E

F S2

S4

S3

H I

G

41


Institutional network

to external network

router

IP subnet

mail server

web server


  All principles seen so far are applicable to a subnet with several switches if there is no cycle in the topology   No cycle = no redundancy in case of failure

  Part of subnet can be disconnected


More than one switch in a subnet

A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83

  Assume frame F has a destination address that is unknown to all switches (not in their forwarding tables)

  Problem frame F is flooded by S1 and then by all other switches and will loop forever

  Solution build a logical spanning tree topology over the real topology

F

Initial frame

F

F

forwardedby S2 and by S3

Problem with cycles

S1 S3

S2

F


  Build a logical tree reaching all LAN segments (here simply called LANrsquos)

  1 Determine the root switch (has the smallest switch id)   Switch id = (priority MAC addr)   Switches regularly flood control

messages (BPDUs) on all their output ports

  BPDU = ltSource switch id root as assumed distance to rootgt

  All switches will soon discover the root id

A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch


Spanning tree (1) Root switch A sends ltAA0gt on LAN1 and LAN2

B sends ltBA1gt on LAN3

Note A laquo LAN segment raquo is sometimes called a laquo collision domain raquo

materialized by a hub but in practice a LAN segment is most often just a cable

43


  2 Build the tree   By continuously receiving these

BPDUs (possibly on several ports) a switch knows its distance to the root and which port leads to the root by that shortest distance (root port r)

  Similar to a DV routing protocol with a distance vector limited to a unique component the root switch

  In practice distances are inversely proportional to link capacities

bull  Remember InvCap

A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr


Spanning tree (2) Root portRoot switch


3 Decide if non-root ports are (data) forwarding or (data) blocking A port is forwarding (f) on a given LAN iff the BPDUs this switch sends on this LAN are smaller than those other switches (would) send

Smaller = shorter distance or equal distance and smaller switch id

Example on LAN6 E sends ltEA2gt G would send ltGA2gt and J would send ltJA3gt So E is elected to be the only one to forward frames on LAN6 J is too far away from the root and G gt E

A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f

Spanning tree (3) Forwarding port

Blocking port


44


  Some switches (eg G and J) are not part of the tree   Another case could be that some ports of some switches are blocking

  They could become part of the tree if another switch or port would fail (leading to no refresh of BPDUs)

  So switches have to listen to BPDUs on blocking ports to detect failures

1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN

Switch thatis part of the

spanning tree

Switch that isnot part of thespanning tree

I

The resulting spanning tree Routing on a spanning tree is not optimal

Same spanning tree for all source-destination pair

Compare to layer-3 routing



Switches vs routers

both are store-and-forward  routers network-layer

devices (examine network-layer headers)

 switches link-layer devices (examine link-layer headers)

both have forwarding tables  routers compute tables using

routing algorithms IP addresses

 switches learn forwarding table using flooding learning MAC addresses


link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison

hubs routers switches

traffic isolation

no yes yes

plug amp play yes no yes

optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer


  62 Error detection   63Multiple access





46


Data center networks   10rsquos to 100rsquos of thousands of hosts often closely

coupled in close proximity   e-business (eg Amazon)   content-servers (eg YouTube Akamai Apple Microsoft)   search engines data mining (eg Google)

  challenges o multiple applications

each serving massive numbers of clients

o managingbalancing load avoiding processing networking data bottlenecks Inside a 40-ft Microsoft container

Chicago data center


Serverracks

TORswitches(TopOfRack)

Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet

load balancer application-layer routing  receives external client requests  directs workload within data center  returns results to external client

(hiding data center internals from client)

Data center networks

47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8

  rich interconnection among switches racks o  increased throughput between racks (multiple

routing paths possible) o  increased reliability via redundancy



Link Layer







48


Synthesis a day in the life of a web request

  journey down protocol stack complete   application transport network link

  putting-it-all-together synthesis   goal identify review understand protocols (at

all layers) involved in seemingly simple scenario requesting www page

  scenario student attaches laptop to campus network requestsreceives wwwgooglecom


A day in the life scenario

Comcast network 68800013

Googlersquos network 64233160019 64233169105

web server

DNS server

school network 68802024

web page

browser

49


router (runs DHCP)

A day in the lifehellip connecting to the Internet

  connecting laptop needs to get its own IP address addr of first-hop router addr of DNS server use DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP

  DHCP request encapsulated in UDP encapsulated in IP encapsulated in 8023 Ethernet

  Ethernet frame broadcast (dest FFFFFFFFFFFF) on LAN received at router running DHCP server (+ switch learning)

  Ethernet demuxed to IP demuxed UDP demuxed to DHCP


router (runs DHCP)

  DHCP server formulates DHCP ACK containing clientrsquos IP address IP address of first-hop router for client name amp IP address of DNS server

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

  encapsulation at DHCP server frame forwarded (switch learning) through LAN demultiplexing at client

Client now has IP address knows name amp addr of DNS server IP address of its first-hop router

  DHCP client receives DHCP ACK reply


50


router (runs DHCP)

A day in the lifehellip ARP (before DNS before HTTP)

  before sending HTTP request need IP address of wwwgooglecom DNS

DNS UDP

IP Eth Phy

DNS

DNS

DNS

  DNS query created encapsulated in UDP encapsulated in IP encapsulated in Eth To send frame to router need MAC address of router interface ARP

  ARP query broadcast received by router which replies with ARP reply giving MAC address of router interface

  client now knows MAC address of first hop router so can now send frame containing DNS query

ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS

  IP datagram containing DNS query forwarded via LAN switch from client to 1st hop router

  IP datagram forwarded from campus network into comcast network routed (tables created by RIP OSPF IS-IS andor BGP routing protocols) to DNS server

  demuxrsquoed to DNS server   DNS server replies to client with

IP address of wwwgooglecom (perhaps after querying other DNS servers)


DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

A day in the lifehellip using DNS

51


router (runs DHCP)

A day in the lifehellipTCP connection carrying HTTP

HTTP TCP IP Eth Phy

HTTP

  to send HTTP request client first opens TCP socket to web server

  TCP SYN segment (step 1 in 3-way handshake) inter-domain routed to web server

  TCP connection established 64233169105 web server

SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

  web server responds with TCP SYNACK (step 2 in 3-way handshake)


router (runs DHCP)

A day in the lifehellip HTTP requestreply HTTP TCP IP Eth Phy

HTTP

  HTTP request sent into TCP socket

  IP datagram containing HTTP request routed to wwwgooglecom

  IP datagram containing HTTP reply routed back to client

64233169105 web server

HTTP TCP IP Eth Phy

  web server responds with HTTP reply (containing web page)

HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

  web page finally () displayed

52


Chapter 6 Summary   principles behind data link layer services

  error detection   sharing a broadcast channel multiple access   link layer addressing

  instantiation and implementation of various link layer technologies   Ethernet   switched LANs

bull  learning building spanning tree   evolution of the term ldquolinkrdquo

  1 physical wire connecting two communicating nodes   2 physical channel

bull  point-to-point or shared wire bull  ldquowirerdquo could also be radio spectrum

  3 complex switch infrastructure   all these ldquolinksrdquo still viewed by IP as a layer 2 ldquochannelrdquo


Chapter 6 letrsquos take a breath   journey down protocol stack complete (except PHY)

  solid understanding of networking principles practice

  hellip could stop here hellip but lots of interesting topics   wireless networks and mobility   content distribution and multimedia applications   engineering networks to provide better quality to apps   advanced routing and traffic engineering   securing networks   managing networks

2


Link Layer








Link Layer Introduction Some terminology   hosts and routers are nodes

  = devices with a network layer (L3)   communication channels that

connect adjacent nodes along communication path are links   wired links   wireless links   LANs

  layer-2 packet is a frame encapsulates datagram

data-link layer has responsibility of transferring datagram from one node to physically adjacent node over a link

global ISP

3












algorithm








4















software firmware

controller


cpu memory

host bus (eg PCI)



link

link physical

5









datagram datagram

datagram

frame


Link Layer







6




otherwise






0 0

7

















ltDRgt =

=

8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













3












algorithm








4















software firmware

controller


cpu memory

host bus (eg PCI)



link

link physical

5









datagram datagram

datagram

frame


Link Layer







6




otherwise






0 0

7

















ltDRgt =

=

8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













4















software firmware

controller


cpu memory

host bus (eg PCI)



link

link physical

5









datagram datagram

datagram

frame


Link Layer







6




otherwise






0 0

7

















ltDRgt =

=

8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













5









datagram datagram

datagram

frame


Link Layer







6




otherwise






0 0

7

















ltDRgt =

=

8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













6




otherwise






0 0

7

















ltDRgt =

=

8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













7

















ltDRgt =

=

8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













8


CRC Example Want




or R = D2r mod G

euro


G⎡

⎣ ⎢

⎤

⎦ ⎥

Quotient

Dividend


10011001

1

101

01011

00010101001

1100001100100110101001 011

101110

D

Divisor

G r = 3

000

Remainder





D(x) = x5 + x3 + x2 + x r=3 G(x) = x3 + 1

euro


G(x)⎡

⎣ ⎢

⎤

⎦ ⎥

R(x) = x + 1

9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













9




















10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













10












Link Layer







11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













11
















12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













12








4 simple







longer turns

13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













13




256 idle

1 3 4 1 3 4

6-slot frame



bands 256 idle

freq

uenc

y ba

nds time

FDM cable

14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













14









Slotted ALOHA











15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













15


Slotted ALOHA




  simple




1 1 1 1

2

3

2 2

3 3

node 1

node 2

node 3

C C C S S S E E E








Np(1-p)N-1 = (1-1N)N-1




euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG

16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













16





In frame time units



= p (1-p)2(N-1)



= 1(2e) = 018


17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













17







  ALOHA G e-2G


euro

limNrarrinfin

1minus GN

⎛

⎝ ⎜

⎞

⎠ ⎟ N

= eminusG





frame

Ideal S = G

18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













18












19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













19









p-persistent CSMA


Efficiency



frame

Ideal

20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













20













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













21








A B

(a)

A B

(b)

A B

(c)

A B







22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













22














Channel efficiency

S10

09

08

07

06

05

04

03

02

01

0 1 2 4 8 16 32 64 128 256

1024 byte frames

512 byte frames

256 byte frames

128 byte frames

64 byte frames




Incr

easi

ng f

ram

e si

ze

23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













23













failure (master)

master

slaves

poll

data

data

24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













24








T

data

(nothing to send)

T


cable headend

CMTS

ISP







hellip

hellip



25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













25








Upstream channel j

t1 t2



cable headend

CMTS









26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













26


Link Layer














27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













27



adapter

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53









28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













28







1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-66-F7-2B-08-53

LAN

137196723

137196778

137196714

137196788









address (unicast)






29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













29




R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy

IP src 111111111111 IP dest 222222222222



30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













30


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP Eth Phy


IP Eth Phy



IP src 111111111111 IP dest 222222222222

IP src 111111111111 IP dest 222222222222


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B


IP src 111111111111 IP dest 222222222222




IP Eth Phy

IP Eth Phy

31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













31


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

IP Eth Phy


R

1A-23-F9-CD-06-9B 222222222220

111111111110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D

111111111112

111111111111 74-29-9C-E8-FF-55

A 222222222222 49-BD-D2-C7-56-2A

222222222221 88-B2-2F-54-1A-0F

B



IP src 111111111111 IP dest 222222222222


IP Eth Phy

32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













32


Link Layer










33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













33






hub or switch

bus coaxial cable

star





hub

34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













34





switch






dest address

source address


type

35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













35








dest address

source address


type







36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













36






link physical


100BASE-TX

100BASE-T4





Link Layer







37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













37















A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6

38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













38





A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5







A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6





A Arsquo




39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













39








A

Arsquo

B

Brsquo C

Crsquo

1 2

3 4 5

6







flood

Arsquo A


Arsquo 4 60


40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













40





A

B

S1

C D

E

F S2

S4

S3

H I

G




A

B

S1

C D

E

F S2

S4

S3

H I

G

41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













41



to external network

router

IP subnet

mail server

web server






A

B

S1

C D

E

F S2

S4

S3

H I

G

42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













42

DataLink Layer 6-83




F

Initial frame

F

F


Problem with cycles

S1 S3

S2

F







A B2

C31

LAN

4

G

I

D E F

6 75

H J8 9

Switch






43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













43







A B2

C31 4

G

I

D E F

6 75

H J8 9

r

r

r

rr

r

r

rr







A B2

C31 4

G

I

D E F

6 75

H J8 9

rf

r

r

rr

r

r

rr

f f f

f f f

f f


Blocking port


44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













44





1 2 3 4

5 6 7

8 9

A B C

D E F

H

LAN


spanning tree


I






Switches vs routers








link physical

network link

physical

link physical

switch

datagram


link physical

frame

frame

frame datagram

45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













45


Summary comparison


traffic isolation

no yes yes


optimal routing

no yes no

cut through

yes no yes

Some do


Link Layer







46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













46







Chicago data center


Serverracks


Tier-1switches

Tier-2switches

Loadbalancer

Loadbalancer

B

1 2 3 4 5 6 7 8

A C

Borderrouter

Accessrouter

Internet




47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













47


Serverracks

TORswitches

Tier-1switches

Tier-2switches

1 2 3 4 5 6 7 8





Link Layer







48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













48











web server

DNS server


web page

browser

49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













49


router (runs DHCP)



DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP DHCP





router (runs DHCP)


DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP UDP

IP Eth Phy

DHCP

DHCP

DHCP

DHCP

DHCP





50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













50


router (runs DHCP)



DNS UDP

IP Eth Phy

DNS

DNS

DNS




ARP query

Eth Phy

ARP

ARP

ARP reply


router (runs DHCP)

DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS

DNS






DNS server DNS UDP

IP Eth Phy

DNS

DNS

DNS

DNS


51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













51


router (runs DHCP)


HTTP TCP IP Eth Phy

HTTP




SYN

SYN

SYN

SYN

TCP IP

Eth Phy

SYN

SYN

SYN

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK

SYNACK



router (runs DHCP)


HTTP





HTTP TCP IP Eth Phy


HTTP

HTTP

HTTP HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP

HTTP


52













52













Documents

Introduction to Computer Networking Guy Leduc Chapter 6leduc/cours/IRI/IRI-ch6.pdf · · 2017-12-0611 © From Computer Networking, by Kurose&Ross DataLink Layer 6-21 Multiple Access