DataCom Introduction

8/8/2019 DataCom Introduction

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Introduction 1-1

Data Communicationand Networking

A Top Down ApproachGhana Telecom University College

Credit : Jim Kurose, Keith Ross & Addison-Wesley



Introduction 1-2

GOAL:The main goal of the course is to study data

communication and network characteristics that

affects transmission. The INTERNET will be in focus,

considering the top ² down approach.

It therefore implies that focus will also be given to thefive-layer Internet architecture rather than the

seven-layer OSI architecture



Introduction 1-3

Chapter 1: IntroductionOverview:

Recap of Data Communication and the Internetwhat·s a protocol?

network edge; hosts, access net, physical medianetwork core: packet/circuit switching, Internetstructureperformance: loss, delay, throughput

securityprotocol layers, service modelshistory



Introduction 1-4

Data Networks: recapDescription

Formulate

Components:Info/Message, transmitter, receiver, protocol & channel

Discuss types and topologies

routerserverwired

links

accesspoints PC

wirelesslaptop

cellularhandheld



Introduction 1-5

Internet: Terminologies

World wide computer network made up ofmillions of connected computing devices.

End devices on the internet are termed as nodeor hosts or end systems which run networkapplications.Protocols - End systems run protocols that

control the sending and receiving of informationwithin the Internet.E.g. TCP/IP- main protocol of the Internet.HTTP, FTP, SMTP, Ethernet, etc



Introduction 1-6

Internet: Terminologies

Protocols govern all communication activities inInternet. Protocols define format, order ofmessages sent and received among network

entities, and actions taken on the transmissionand/or receipt of a message

Communication links- End systems are connectedtogether by fiber, copper, radio, satellite, etc

transmission rate = bandwidthRouters - Switching devices through which endsystems are indirectly connected to each other.



Introduction 1-7

Interconnection & Routes visualizationViews of the Internet

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

Visualization from the Opte Project of thevarious routes through a portion of theInternet (Source-Wikipedia.org)

Simple interconnection of network devices



Introduction 1-8

Internet

Internet (Structure): ńetwork of networksµloosely hierarchicalpublic Internet versus private intranet

Internet standardsRFC: Request for comments

IETF: Internet Engineering Task Force



Introduction 1-9

Internet: a service view

Distributed applications - A distributedapplication runs on end systems and exchangesdata via the Data Network. E.g . Web, VoIP,email, games, e-commerce, file sharing.Communication infrastructure of Internetenables distributed applications.Communication services provided to applications:

reliable data delivery from source todestination (Connection ² Oriented) ´best effortµ (unreliable) data delivery(Connectionless)

Timely delivery not guaranteed



Introduction 1-10

A closer look at network structure:network edge:applications andhosts

access networks,physical media:wired, wirelesscommunication links

network core:interconnectedroutersnetwork of

networks



Introduction 1-11

The network edge:end systems (hosts):

run application programse.g. Web, emailat édge of networkµ

client/server

peer-peer

client/server modelclient host requests, receivesservice from always-on servere.g. Web browser/server;email client/server

peer-peer model:minimal (or no) use of

dedicated serverse.g. Skype, BitTorrent



Introduction 1-12

Access networks and physical media

Q: How to connect endsystems to edge router?residential access netsinstitutional accessnetworks (school,company) mobile access networks

Keep in mind:bandwidth (bits persecond) of accessnetwork?shared or dedicated?



Introduction 1-13

Residential access: point to point access

Dialup via modemup to 56Kbps direct access torouter (often less)

Can·t surf and phone at sametime: can·t be álways onµ

DSL: digital subscriber linedeployment: telephone company (typically) up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central office



Introduction 1-14

Company access: local area networks

company/univ local areanetwork (LAN) connectsend system to edge routerEthernet:

10 Mbs, 100Mbps,1Gbps, 10Gbps Ethernetmodern configuration:end systems connect

into Ethernet switch



Introduction 1-15

Wireless access networks

shared wireless accessnetwork connects end systemto router

via base station aka áccess

pointµwireless LANs:802.11b/g (WiFi): 11 or 54 Mbps

wider-area wireless accessprovided by telco operator

basestation

mobilehosts

router



Introduction 1-16

Home networks

Typical home network components:DSL or cable modemrouter/firewall/NAT Ethernetwireless accesspoint

wirelessaccesspoint

wirelesslaptops

router/firewallcablemodemto/from

cableheadend

Ethernet



Introduction 1-17

Physical Media

Bit: propagates betweentransmitter/rcvr pairsphysical link: what lies

between transmitter &receiverguided media:

signals propagate in solidmedia: copper, fiber, coax

unguided media:signals propagate freely,e.g., radio

Twisted Pair (TP) two insulated copperwires

Category 3: traditional

phone wires, 10 MbpsEthernetCategory 5:100Mbps Ethernet



Introduction 1-18

Physical Media: coax, fiber

Coaxial cable:two concentric copperconductorsbidirectionalbaseband:

single channel on cablelegacy Ethernet

broadband:multiple channels on

cableHFC

Fiber optic cable:glass fiber carrying lightpulses, each pulse a bithigh-speed operation:

high-speed point-to-pointtransmission (e.g., 10·s-100·s Gps)

low error rate: repeatersspaced far apart ; immuneto electromagnetic noise



Introduction 1-19

Physical media: radio

signal carried inelectromagneticspectrumno physical ´wireµbidirectionalpropagationenvironment effects:

reflection

obstruction by objectsinterference

Radio link types:terrestrial microwave

e.g. up to 45 Mbps channelsLAN(e.g., Wifi)

11Mbps, 54 Mbpswide-area (e.g., cellular)

3G cellular: ~ 1 Mbpssatellite

Kbps to 45Mbps channel (ormultiple smaller channels) 270 msec end-end delaygeosynchronous versus lowaltitude



Introduction 1-20

The Network Core

mesh of interconnectedroutersthe fundamental

question: how is datatransferred through net?circuit switching:dedicated circuit percall: telephone netpacket-switching: datasent thru net indiscrete ćhunksµ



Introduction 1-21

Network Core: Circuit Switching

End-end resourcesreserved for ćallµlink bandwidth, switchcapacitydedicated resources:no sharingcircuit-like

(guaranteed) performancecall setup required





Introduction 1-23

Circuit Switching: FDM and TDM

FDM

frequency

time

TDM

frequency

time

4 usersExample:



Introduction 1-24

Network Core: Packet Switchingeach end-end data stream

divided into packetsuser A, B packets sharenetwork resourceseach packet uses full linkbandwidthresources used as needed

resource contention:aggregate resourcedemand can exceedamount availablecongestion: packetsqueue, wait for link usestore and forward:packets move one hop

at a timeNode receives completepacket before forwarding

Bandwidth division into ́ piecesµDedicated allocationResource reservation



Introduction 1-25

Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern,bandwidth shared on demand s tati s tical multiplexing .

TDM: each host gets same slot in revolving TDM frame.

A

B

C100 Mb/sEthernet

1.5 Mb/s

D E

s tati s tical multiplexing

queue of packetswaiting for output

link





Introduction 1-27

Packet switching versus circuit switching

1 Mb/s linkeach user:

100 kb/s when áctiveµactive 10% of time

circuit-switching:10 users

packet switching:with 35 users,probability > 10 activeat same time is lessthan .0004

Packet switching allows more users to use network!

N users1 Mbps link

Q: how did we get value 0.0004?



Introduction 1-28

Performance

packets queue in router bufferspacket arrival rate to link exceeds output linkcapacitypackets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay) free (available) buffers: arriving packets

dropped ( loss) if no free buffers

How do loss and delay occur?





Introduction 1-30

Delay in packet-switched networks3. Transmission delay:

R=link bandwidth (bps) L=packet length (bits) time to send bits intolink = L/R

4. Propagation delay:d = length of physical links = propagation speed inmedium (~2x108 m/sec) propagation delay = d/s

A

B

propagation

transmission

nodal

processing queueing

Note: s and R are verydifferent quantities!



Introduction 1-31

Nodal delay

dproc = processing delaytypically a few microsecs or less

dqueue = queuing delaydepends on congestion

dtrans = transmission delay

= L/R, significant for low-speed linksdprop = propagation delay

a few microsecs to hundreds of msecs

proptransqueue procnodald d d d d !

Nodal delay di sc ussed : http://www.d.umn.edu/~gshute/net/delays-losses.html



Introduction 1-32

´Realµ Internet delays and routes

1 cs-gw ( 128.119.2 40 .25 4) 1 ms 1 ms 2 ms2 border 1 -rt-fa 5 -1 -0 .gw .umass .edu ( 128.119.3.1 45 ) 1 ms 1 ms 2 ms3 cht-vbns .gw.umass .edu ( 128.119.3.13 0) 6 ms 5 ms 5 ms

4 jn1

-at1

-0-0-19.

wor .vbns

.net (

204

.147

.132.129)

16 ms

11ms

13ms5 jn1 -so7-0-0-0 .wae .vbns .net ( 2 04 .1 47 .13 6 .13 6) 21 ms 18 ms 18 ms

6 abilene-vbns .abilene .ucaid .edu ( 198.32.11.9 ) 22 ms 18 ms 22 ms7 nycm-wash .abilene .ucaid .edu ( 198.32.8. 46) 22 ms 22 ms 22 ms8 62. 40 .1 03.253 (6 2. 40 .1 03.253 ) 1 04 ms 1 09 ms 1 06 ms9 de 2 -1. de 1. de .geant .net (6 2. 40 .9 6 .129 ) 1 09 ms 1 02 ms 1 04 ms1 0 de .fr 1. fr .geant .net (6 2. 40 .9 6 .5 0) 113 ms 121 ms 11 4 ms11 renater-gw .fr 1. fr .geant .net (6 2. 40 .1 03.5 4) 112 ms 11 4 ms 112 ms12 nio-n 2. cssi .renater .fr (193.51.2 06 .13 ) 111 ms 11 4 ms 11 6 ms13 nice .cssi .renater .fr (195.22 0 .98.1 02 ) 123 ms 125 ms 12 4 ms1 4 r 3 t2 -nice .cssi .renater .fr (195.22 0 .98.11 0) 12 6 ms 12 6 ms 12 4 ms15 eurecom-valbonne .r 3 t2. ft.net ( 193. 48.5 0 .5 4) 135 ms 128 ms 133 ms1 6 19 4 .21 4 .211.25 (19 4 .21 4 .211.25 ) 12 6 ms 128 ms 12 6 ms1 7 * * *18 * * *19 fantasia .eurecom .fr (193.55.113.1 42 ) 132 ms 128 ms 13 6 m s

traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements fromgaia.cs.umass.edu to cs-gw.cs.umass.edu

* means no response (probe lost, router not replying)

trans-oceaniclink



Introduction 1-33

Packet loss

queue (aka buffer) preceding link in buffer hasfinite capacitypacket arriving to full queue dropped (aka lost) lost packet may be retransmitted by previousnode, by source end system, or not at all

A

B

packet being transmitted

packet arriving tofull buffer is lost

buffer(waiting area)



Introduction 1-34

Throughputthroughput: rate (bits/time unit) at whichbits transferred between sender/receiver

instantaneous : rate at given point in time

average: rate over longer period of time

server, withfile of F bits

to send to client

link capacityRs bits/sec

link capacityRc bits/sec

pipe that can carryfluid at rateRs bits/sec)

pipe that can carryfluid at rateRc bits/sec)

server sends bits(fluid) into pipe



Introduction 1-35

Throughput (more) Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

Rs > Rc What is average end-end throughput?

Rs

bits/sec Rc

bits/sec

link on end-end path that constrains end-end throughputbottleneck link



Introduction 1-36

Internet protocol stackapplication: supporting networkapplications

FTP, SMTP, HTTPtransport: process-process datatransfer

TCP, UDPnetwork: routing of datagrams fromsource to destination

IP, routing protocolslink: data transfer betweenneighboring network elements

PPP, Ethernetphysical: bits ón the wireµ

application

transport

network

link

physical



Introduction 1-37

sourceapplicationtransportnetwork

linkphysical

HtHn M

segment Ht

datagram

destination

applicationtransportnetwork

linkphysical

HtHnHl MHtHn M

Ht MM

networklink

physical

linkphysical

Ht

Hn

Hl

MHtHn M

HtHn M

HtHnHl M

router

switch

Encapsulationmessage M

Ht M

Hnframe



Introduction 1-38

Network SecurityThe field of network security is about:

how bad guys can attack computer networkshow we can defend networks against attackshow to design architectures that are immune toattacks

Internet not originally designed with(much) security in mind

original vision: á group of mutually trustingusers attached to a transparent networkµInternet protocol designers playing ćatch-upµSecurity considerations in all layers!



Introduction 1-39

Hackers can put malware into hostsvia Internet

Malware can get in host from a virus, worm, ortrojan horse .

Spyware malware can record keystrokes, websites visited, upload info to collection site.

Infected host can be enrolled in a botnet , usedfor spam and DDoS attacks.

Malware is often self-replicating : from aninfected host, seeks entry into other hosts



Introduction 1-40

Hackers can put malware into hostsvia Internet

Trojan horseHidden part of someotherwise usefulsoftware

Today often on a Webpage (Active-X, plugin) Virus

infection by receivingobject (e.g., e-mail

attachment), activelyexecutingself-replicating:propagate itself toother hosts, users

Worm:infection by passivelyreceiving object that getsitself executed

self- replicating: propagatesto other hosts, usersS apphire Worm: aggregate scans/sec

in first 5 minutes of outbreak (CAIDA, UWisc data)



Introduction 1-41

Hackers can attack servers andnetwork infrastructure

Denial of service (DoS): attackers make resources(server, bandwidth) unavailable to legitimate trafficby overwhelming resource with bogus traffic

1. select target2. break into hosts

around the network(see botnet)

3.send packets towardtarget fromcompromised hosts

target



Introduction 1-42

Hackers can sniff packetsPacket sniffing:

broadcast media (shared Ethernet, wireless) promiscuous network interface reads/records allpackets (e.g., including passwords!) passing by

A

B

C

src:B dest:A payload

Wireshark software used for end-of-chapterlabs is a (free) packet-sniffer





Introduction 1-44

The bad guys can record andplayback

record-and-playback : sniff sensitive info (e.g.,password), and use later

password holder is that user from system point ofview

A

B

C

src:B dest:A user: B; password: foo



Introduction 1-45

Internet History

1961: Kleinrock - queueingtheory showseffectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet conceivedby Advanced ResearchProjects Agency1969: first ARPAnet nodeoperational

1972:ARPAnet public demonstrationNCP (Network Control Protocol)

first host-host protocolfirst e-mail programARPAnet has 15 nodes

1961-1972: Early packet-switching principles



Introduction 1-46

Internet History

1970: ALOHAnet satellitenetwork in Hawaii1974: Cerf and Kahn -architecture for

interconnecting networks1976: Ethernet at XeroxPARCate70·s: proprietaryarchitectures: DECnet, SNA,XNA

late 70·s: switching fixedlength packets (ATMprecursor) 1979: ARPAnet has 200 nodes

Cerf and Kahn·s internetworkingprinciples:

minimalism, autonomy - nointernal changes requiredto interconnect networksbest effort service modelstateless routersdecentralized control

define today·s Internetarchitecture

1972-1980: Internetworking, new and proprietary nets



Introduction 1-47

Internet History

1983: deployment ofTCP/IP1982: smtp e-mailprotocol defined1983: DNS definedfor name-to-IP-address translation

1985: ftp protocoldefined1988: TCP congestioncontrol

new national networks:Csnet, BITnet,NSFnet, Minitel

100,000 hostsconnected toconfederation ofnetworks

1980-1990: new protocols, a proliferation of networks



Introduction 1-48

Internet History

Early 1990·s: ARPAnetdecommissioned1991: NSF lifts restrictions oncommercial use of NSFnet(decommissioned, 1995) early 1990s: Web

hypertext [Bush 1945, Nelson1960·s]HTML, HTTP: Berners-Lee1994: Mosaic, later Netscapelate 1990·s:commercialization of the Web

Late 1990·s ² 2000·s:more killer apps: instantmessaging, P2P file sharing

network security toforefrontest. 50 million host, 100million+ usersbackbone links running at

Gbps

1990, 2000·s: commercialization, the Web, new apps



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DataCom Introduction