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Introduction to computer networking
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Text, audio, image and video: multimedia communications in the Internet
“www.youtube.com” server
Browser
bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits bits
and more bits…
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Coding black and white images
pixel
grey level = luminance
5
Coding black and white images
1 bit/pixel21 levels
black = 0white = 1
2 bits/pixel22 levels
black = 00
dark grey = 01
light grey = 10
white = 11
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Coding black and white images
3 bits/pixel23 levels
black = 0000
… = 0001
… = 0010
… = 0011
… = 0100
… = 0101
… = 0110
… = 0111
black = 000very very dark grey
= 001
very dark grey = 010dark grey = 011ligth grey = 100very light grey = 101very very light grey
= 110
white = 111
4 bits/pixel24 levels
… = 1000
… = 1001
… = 1010
… = 1011
… = 1100
… = 1101
… = 1110
white = 1111
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Coding black and white images
luminance (8 bits/pixel = 256 grey levels)
576 lines X 720 columns = 414720 pixels
414720 pixels X 8 bits/pixel
= 3.318 Megabits
pixel
87 89 101
106
118 130 142 155
85 91 101
105
116 129 135 149
86 92 96 105
112 128 131 144
92 88 102
101
116 129 135 147
88 94 94 98 113 122 130 139
88 95 98 97 113 119 133 141
92 99 98 106
107 118 135 145
89 95 98 107
104 112 130 144
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Luminance + (two) Chrominances = 576 X 720 + 2 X 576 X 360 = 829440 pixels
829440 pixels X 8 bits/pixel X 25 images/s =
166 Mbits/s
Colour and motion – video coding
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Compression is needed… and possible!
Voice at 64 Kbits/s Music at 1.4 Mbit/s Video at 166 Mbit/s
Compression explores redundancy and
irrelevance in multimedia information
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Compression is needed … and possible
11
Compression systems
Serviço Resolução espacial
Resolução temporal Bits/amostra Débito
binário (PCM)Débito binário
codificadoFactor de
compressão
Full HD1080p
1080 19201080 960
25 imagens/s
progressivas
8 bits/amostra 830 Mbit/s 8-10 Mbit/s 80-100
HD Ready720p
720 1280720 640
25 imagens/s
progressivas
8 bits/amostra 370 Mbit/s 6-8 Mbit/s 60
TV e DVD standard (MP4)
576 720576 360
25 imagens/s
entrelaçadas8
bits/amostra 166 Mbit/s 6 Mbit/s 27.5
Internet streaming (MP4)
288 360 144 180
25 imagens/s
progressivas8
bits/amostra 31 Mbit/s 150 kbit/s 200
Vídeo móveis (MP4)
144 180 72 90
25 imagens/s
progressivas
8 bits/amostra 7.8 Mbit/s 100 kbit/s 80
Música stereo (MP3) - 44000
amostras/s16
bits/amostra 1.4 Mbit/s 100 kbit/s 14
Voz (GSM) - 8000 amostras/s
8 bits/amostra 64 kbit/s 13 kbit/s 5
12
01100101
Internet: a packet switching network
1100
0101 Internet
packet
13
Internet
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
Packet“Surfing the net”
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00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
Routing packets
link
router
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00001010100100101101101001101110 Routing packets
link
router
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
00001010100100101101101001101110
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ISP
ISP
Domestic network
Organizational network
Mobile network
Internet structure: network of networks
Router
Internet
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Internet structure: network of networks
roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,
Cable and Wireless), national/international coverage treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers
interconnect (peer)
privately
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Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
….
………
POP: point-of-presence
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Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2
ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for
connectivity to rest of Internet tier-2 ISP is
customer oftier-1 provider
Tier-2 ISPs also peer
privately with each other.
20
Internet structure: network of networks
“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier- 3 ISPs
are customers of
higher tier ISPs
connecting them to rest of Internet
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Internet structure: network of networks
a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
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Internet
128.45.233.8
128.45.233.7
192.26.1.29
192.26.1.30
192.26.5.83192.26.5.84
192.26.12.1128.45.233.6
Internet addressing
193 . 32 . 216 . 911000001 00100000 11011000 00001001
Rosário
Matilde
Teresa
Rui
Pedro
João
IP address
128.45.138.1
153.3.2.211.15.2.33
11.23.35.2
192.26.1.1192.26.5.1
153.3.2.1
153.4.2.2
153.4.2.1
15.54.18.20 20.18.3.1
20.18.3.2
192.26.12.1
15.53.19.21
Run ipconfig
232 = 4.294.967.296 addresses!
23
128.45.233.8
128.45.233.7
192.26.1.29
192.26.1.30
192.26.5.83192.26.5.84
192.26.12.1128.45.233.6
Internet names - DNS
128.45.138.1
153.3.2.211.15.2.33
11.23.35.2
192.26.1.1192.26.5.1
153.3.2.1
153.4.2.2
153.4.2.1
15.54.18.20 20.18.3.1
20.18.3.2
192.26.12.1
15.53.19.21
Run nslookup
www.ist.utl.pt
beethoven.ist.utl.pt
stravinsky.ist.utl.pt
ravel.ist.utl.pt
alameda.ist.utl.pt
hawai.com
taguspark.ist.utl.pt
praia.edu
bronze.praia.pt
surf.praia.pt
cromo.praia.pt
24
Testing Internet destinations: the ping command
ICMP Echo Request
ICMP Echo Reply
Run ping
25
Discovering Internet routes: traceroute
ICMP Echo Request
ICMP Echo Reply
Do a visual traceroute @
www.yougetsignal.com
ICMP Echo Request
ICMP Time Exceeded
ICMP Time Exceeded
ICMP Echo Request
26Internet crossing oceans
27
Internet crossing oceans
28
Internet paintings
www.visual complexity.com
29
Internet paintings
www.visual complexity.com
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Internet paintings
Convergence, Jackson Pollock (1912-1956)
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Internet access
Internet
24 Mbits/s
Download of: 2 Mbits/s 24 Mb/sWeb page (250 KB) 1 seg 0.083 seg
Music (5 MB) 20 seg 1.7 seg
Video clip (25 MB) 1 min e 40 seg 8.3 seg
Low quality movie (750 MB) 50 min 4 min e 10 seg
High quality movie (4 GB) 4 horas e 27 min
22 min e 13 seg
Download duration =
8X4X109 bits
24X106 bits/s
32
Internet access
Internet
24 Mbits/s
If after half an hour the download has not ended, what went
wrong?
“The Cry”, Edvard Munch (1863-1944)
33
Internet access
24 Mbits/s
2 Mbits/s
server’s access network
Internet
If after half an hour the download has not
ended, what went wrong?
34
Internet access
24 Mbits/s
24 Mbits/s
server’s access network
1 Mbits/s
Internet
If after half an hour the download has not ended, what went
wrong?
35
Internet access: p2p
24 Mbits/s
1 Mb/s1 Mb/s
1 Mb/s
1 Mb/s
Internet
1 Mb/s
24 Mbits/s
1 Mb/s
Internet
36
Packet-switching: store-and-forward
takes L/R seconds to transmit (push out) packet of L bits on to link at R bps
store and forward: entire packet must arrive at router before it can be transmitted on next link
delay = 3L/R (assuming zero propagation delay)
Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay =
15 sec
R R RL
more on delay shortly …
37
Packet Switching: Message Segmenting
Now break up the message into 5000 packets Each packet 1,500
bits 1 msec to transmit
packet on one link pipelining: each link
works in parallel Delay reduced from
15 sec to 5.002 sec
5-38
Communication links
Two types of “links”: 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 HFC 802.11 wireless LAN
shared wire (e.g., cabled Ethernet)
shared RF (e.g., 802.11 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air, acoustical)
39
Communication links – antenna transmission systems
40
Communication links – optical transmission systems
41
Errors in communication links
S/H
DECISION CIRCUIT
AMPLIFIER+
FILTER
V
c(t)
b(t)a(t)
SYNC
RECEIVER
1 0 1 1 0 1 0 0
A
A
A
V
0
1 0 0 1 0 1 1 0
error error
received signal
sampled signal (S/H)
regenerated signal
a(t)
b(t)
c(t)
transmitted signal
Signal degrade due to: Attenuation Distortion Noise Interference
42
What’s a protocol?
a human protocol and a computer network protocol:
Q: Other human protocols?
Hi
Hi
Got thetime?
2:00
time
What’s a protocol?
human protocols: “what’s the time?” “I have a question” introductions
… specific msgs sent … specific actions
taken when msgs received, or other events
network protocols: machines rather than
humans all communication
activity in Internet governed by protocols
43
protocols define format, order of msgs sent and
received among network entities, and actions taken on msg transmission, receipt
TFTP – an example of a network application protocol for file transfer
Internet standard defined in RFC (Request for Comment) by the IETF (Internet Engineering Task Force)
Includes an initial handshake Files are segmented into
messages It is not efficient to transfer a
large file in a single message
TFTP uses the Stop-and-Wait protocol for error control
Messages can be lost, corrupted or received out of order in the network
How is the end of a file transfer signaled?
44
45
Stop-and-wait (SW)
Operation without errors
46
Stop-and-wait (SW)
Error recovery
47
Stop-and-wait (SW)
DATA messages need to be numbered
48
Stop-and-wait (SW)
ACK messages need to be numbered
49
Stop-and-wait (SW)
Ok!
50
TFTP message format
READ REQ (1) FILENAME 0 MODE 0
2 bytes n bytes 1 byte n bytes 1 byte
WRITE REQ (2) FILENAME 0 MODE 0
2 bytes n bytes 1 byte n bytes 1 byte
DATA (3) BLOCK # data
2 bytes 2 bytes up to 512 bytes
ACK (4) BLOCK #
2 bytes 2 bytes
ERROR (5) ERROR CODE ERROR MESSAGE 0
2 bytes 2 bytes n bytes 1 byte
ERROR CODE:00 – Not defined01 – File not found02 – Access violation03 – Disk full04 – Invalid operation code05 – Unknown port number06 – File already exists07 – No such user
51
TFTP write
Host @ 192.168.8.227 sends request to write file f1268.txt (with 1268 bytes) in the server @ 192.168.8.226
The server and client applications are configured to use a maximum message size of 1024 bytes
The second DATA message (Block No. = 2) is detected as the last one because it has a size lower than 1024 bytes (1268 - 1024 = 244 bytes)
52
App-layer protocol defines
Types of messages exchanged, e.g., request, response
Message syntax: what fields in
messages & how fields are delineated
Message semantics meaning of information
in fields Rules for when and
how processes send & respond to messages
Public-domain protocols:
defined in RFCs allows for
interoperability e.g., HTTP, SMTP Click here for the main T
FTP RFC (RFC 1350)
Proprietary protocols: e.g., Skype
Application architectures
Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P
53
54
Client-server architectureserver:
always-on host permanent IP address server farms for scaling
clients: communicate with
server may be intermittently
connected may have dynamic IP
addresses do not communicate
directly with each other
client/server
55
Pure P2P architecture
no always-on server arbitrary end systems
directly communicate peers are
intermittently connected and change IP addresses
example: Gnutella
Highly scalable but difficult to manage
peer-peer
56
Hybrid of client-server and P2PSkype
voice-over-IP P2P application centralized server: finding address of
remote party client-client connection: direct (not through
server) Instant messaging
chatting between two users is P2P centralized service: client presence
detection/location• user registers its IP address with central
server when it comes online• user contacts central server to find IP
addresses of buddies
57
Processes communicating
Process: program running within a host.
within same host, two processes communicate using inter-process communication (defined by OS).
processes in different hosts communicate by exchanging messages
Client process: process that initiates communication
Server process: process that waits to be contacted
Note: applications with P2P architectures have client processes & server processes
58
Sockets
process sends/receives messages to/from its socket
socket analogous to door sending process shoves
message out door sending process relies on
transport infrastructure on other side of door which brings message to socket at receiving process
process
TCP withbuffers,
variables
socket
host orserver
process
TCP withbuffers,
variables
socket
host orserver
Internet
controlledby OS
controlled byapp developer
API: (1) choice of transport protocol; (2) ability to fix a few parameters
59
Addressing processes to receive messages,
process must have identifier
host device has unique 32-bit IP address
Q: does IP address of host on which process runs suffice for identifying the process?
identifier includes both IP address and port numbers associated with process on host.
Example port numbers: HTTP server: 80 Mail server: 25
to send HTTP message to gaia.cs.umass.edu web server: IP address:
128.119.245.12 Port number: 80
more shortly…
A: No, many processes can be running on same host
60
What transport service does an app need?Data loss some apps (e.g., audio)
can tolerate some loss other apps (e.g., file
transfer, telnet) require 100% reliable data transfer
Timing some apps (e.g.,
Internet telephony, interactive games) require low delay to be “effective”
Bandwidth some apps (e.g., multimedia) require minimum amount of
bandwidth to be “effective”
other apps (“elastic apps”) make use of whatever bandwidth
they get
61
Transport service requirements of common apps
Application
file transfere-mail
Web documentsreal-time audio/video
stored audio/videointeractive gamesinstant messaging
Data loss
no lossno lossno loss
loss-tolerant
loss-tolerantloss-tolerant
no loss
Bandwidth
elasticelasticelastic
audio: 5kbps-1Mbpsvideo:10kbps-5Mbps
same as above few kbps up
elastic
Time Sensitive
nonono
yes, 100’s msec
yes, few secsyes, 100’s msec
yes and no
62
Protocol “Layers”Networks are
complex! many “pieces”:
hosts routers links of various
media applications protocols hardware,
software
Question: Is there any hope of organizing structure
of network?
Or at least our discussion of
networks?
63
Organization of air travel
a series of steps
ticket (purchase)
baggage (check)
gates (load)
runway takeoff
airplane routing
ticket (complain)
baggage (claim)
gates (unload)
runway landing
airplane routing
airplane routing
64
ticket (purchase)
baggage (check)
gates (load)
runway (takeoff)
airplane routing
departureairport
arrivalairport
intermediate air-trafficcontrol centers
airplane routing airplane routing
ticket (complain)
baggage (claim
gates (unload)
runway (land)
airplane routing
ticket
baggage
gate
takeoff/landing
airplane routing
Layering of airline functionality
Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below
65
Why layering?
Dealing with complex systems: explicit structure allows identification,
relationship of complex system’s pieces layered reference model for discussion
modularization eases maintenance, updating of system change of implementation of layer’s service
transparent to rest of system e.g., change in gate procedure doesn’t
affect rest of system layering considered harmful?
66
Internet protocol stack application: supporting network
applications FTP, SMTP, HTTP
transport: process-process data transfer TCP, UDP
network: routing of datagrams from source to destination IP, routing protocols
link: data transfer between neighboring network elements PPP, Ethernet
physical: bits “on the wire”
application
transport
network
link
physical
67
sourceapplicatio
ntransportnetwork
linkphysical
HtHn M
segment Ht
datagram
destination
application
transportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHn M
HtHnHl M
router
switch
Encapsulationmessage M
Ht M
Hn
frame
68
Internet transport protocols services
TCP service: connection-oriented: setup
required between client and server processes
reliable transport between sending and receiving process
flow control: sender won’t overwhelm receiver
congestion control: throttle sender when network overloaded
does not provide: timing, minimum bandwidth guarantees
UDP service: unreliable data transfer
between sending and receiving process
does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee
Q: why bother? Why is there a UDP?
69
Internet apps: application, transport protocols
Application
e-mailremote terminal access
Web file transfer
streaming multimedia
Internet telephony
Applicationlayer protocol
SMTP [RFC 2821]Telnet [RFC 854]HTTP [RFC 2616]
FTP [RFC 959]proprietary
(e.g. RealNetworks)proprietary
(e.g., Vonage,Dialpad)
Underlyingtransport protocol
TCPTCPTCPTCP
TCP or UDP
typically UDP
70
Transport services and protocols provide logical
communication between app processes running on different hosts
transport protocols run in end systems send side: breaks app
messages into segments, passes to network layer
rcv side: reassembles segments into messages, passes to app layer
more than one transport protocol available to apps Internet: TCP and UDP
application
transportnetworkdata linkphysical
application
transportnetworkdata linkphysical
logical end-end transport
71
Multiplexing/demultiplexing
application
transport
network
link
physical
P1 application
transport
network
link
physical
application
transport
network
link
physical
P2P3 P4P1
host 1 host 2 host 3
= process= socket
delivering received segmentsto correct socket
Demultiplexing at rcv host:gathering data from multiplesockets, enveloping data with header (later used for demultiplexing)
Multiplexing at send host:
72
How demultiplexing works host receives IP datagrams
each datagram has source IP address, destination IP address
each datagram carries 1 transport-layer segment
each segment has source, destination port number
host uses IP addresses & port numbers to direct segment to appropriate socket
source port # dest port #
32 bits
applicationdata
(message)
other header fields
TCP/UDP segment format
73
Connectionless demultiplexing Create sockets with port
numbers:DatagramSocket mySocket1 = new
DatagramSocket(12534);DatagramSocket mySocket2 = new
DatagramSocket(12535);
UDP socket identified by two-tuple:
(dest IP address, dest port number)
When host receives UDP segment: checks destination port
number in segment directs UDP segment to
socket with that port number
IP datagrams with different source IP addresses and/or source port numbers directed to same socket
74
Connectionless demultiplexing
DatagramSocket serverSocket = new DatagramSocket(6428);
clientIP:B
P2
client IP: A
P1P1P3
serverIP: C
SP: 6428
DP: 9157
SP: 9157
DP: 6428
SP: 6428
DP: 5775
SP: 5775
DP: 6428
SP provides “return address”
75
TFTP read
76
TFTP read
77
UDP: User Datagram Protocol [RFC 768]
“no frills,” “bare bones” Internet transport protocol
“best effort” service, UDP segments may be: lost delivered out of order
to app connectionless:
no handshaking between UDP sender, receiver
each UDP segment handled independently of others
Why is there a UDP? no connection
establishment (which can add delay)
simple: no connection state at sender, receiver
small segment header no congestion control:
UDP can blast away as fast as desired
78
UDP: more often used for streaming
multimedia apps loss tolerant rate sensitive
other UDP uses DNS SNMP
reliable transfer over UDP: add reliability at application layer application-specific
error recovery!
source port # dest port #
32 bits
Applicationdata
(message)
UDP segment format
length checksumLength, in
bytes of UDPsegment,including
header
79
UDP checksum
Sender: treat segment contents
as sequence of 16-bit integers
checksum: addition (1’s complement sum) of segment contents
sender puts checksum value into UDP 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 nonetheless? More later ….
Goal: detect “errors” (e.g., flipped bits) in transmitted segment
80
Internet Checksum Example Note
When adding numbers, a carryout from the most significant bit needs to be added to the result
Example: add two 16-bit integers
1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1
1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1
wraparound
sumchecksum
4-81
Network layer transport segment
from sending to receiving host
on sending side encapsulates segments into datagrams
on rcving side, delivers segments to transport layer
network layer protocols in every host, router
router examines header fields in all IP datagrams passing through it
application
transportnetworkdata linkphysical
application
transportnetworkdata linkphysical
networkdata linkphysical network
data linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysicalnetwork
data linkphysical
4-82
Two Key Network-Layer Functions
forwarding: move packets from router’s input to appropriate router output
routing: determine route taken by packets from source to dest.
routing algorithms
analogy:
routing: process of planning trip from
source to dest
forwarding: process of getting through single interchange
4-83
IP datagram format
ver length
32 bits
data (variable length,typically a TCP
or UDP segment)
16-bit identifier
header checksum
time tolive
32 bit source IP address
IP protocol versionnumber
header length (bytes)
max numberremaining hops
(decremented at each router)
for
fragmentation/reassembly
total datagramlength (bytes)
upper layer protocolto deliver payload to
head.len
type ofservice
“type” of data flgsfragment
offsetupper layer
32 bit destination IP address
Options (if any) E.g. timestamp,record route
taken, specifylist of routers
to visit.
how much overhead with
TCP? 20 bytes of TCP 20 bytes of IP = 40 bytes +
app layer overhead
4-84
IP Addressing: introduction IP address: 32-bit
identifier for host, router interface
interface: connection between host/router and physical link router’s typically
have multiple interfaces
host typically has one interface
IP addresses associated with each interface
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
223.1.1.1 = 11011111 00000001 00000001 00000001
223 1 11
4-85
IP addresses – decimal notation
Classe menor endereço maior endereço
A 1.0.0.0 126.0.0.0
B 128.1.0.0 191.255.0.0
C 192.0.1.0 223.255.255.0
D 224.0.0.0 239.255.255.255
E 240.0.0.0 255.255.255.254
10000000 00001010 00000010 00011110
128 . 10 . 2 . 30
4-86
IP addresses – class-full addressing
hostid0 netid
hostid1 0 netid
hostid1 1 0 netid
0 7 15 23 31
1 1 1 endereço multicast0
Classe A
Classe B
Classe C
Classe D
4-87
IP addresses – address space
Classe # bits no prefixo
# máximo de redes
# bits no sufixo
# máximo de hosts por rede
A 7 128 24 16,777,216
B 14 16,384 16 65,536
C 21 2,097,152 8 256
NOTE: Some of these IP addresses can not be used!
4-88
IP addresses - example
Token-ring192.5.48.0
Ethernet 128.10.0.0
10.0.0.0
router
128.10.2.26
Ethernet host
token ring host
multi-homed host
Ethernet host
128.10.2.8
128.10.2.3
192.5.48.7router
192.5.48.6 10.0.0.37
192.5.48.1
192.5.48.3
128.10.2.70
4-89
Special IP addresses
tudo 0s host
tudo 0s
tudo 1s
net tudo 1s
qualquer (em geral 1)127
ESTE HOST1
host NESTA REDE 1
BROADCAST LOCAL2
BROADCAST DIRIGIDO PARA net2
LOOPBACK 3
1 Permitido apenas na inicialização; nunca é endereço destino válido
2 Nunca é endereço origem válido
3 Nunca deve aparecer na rede
net tudo 0s ESTA net4
4 Reservado para designar a rede
4-90
IP addressing – Mask
Iniatially IP addresses had fixed borders between netid and hostid (classes A, B and C)
Nowadays the border is defined by the network mask
endereço IP
máscara 255.
10. 0.0.1
0.0.0
00001010
11111111
00000000 00000000 00000001
00000000 00000000 00000000
rede hostrede host
decimal binário
4-91
Subnets IP address:
subnet part (high order bits)
host part (low order bits)
What’s a subnet ? device interfaces
with same subnet part of IP address
can physically reach each other without intervening router
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
network consisting of 3 subnets
subnet
4-92
Subnets 223.1.1.0/24223.1.2.0/24
223.1.3.0/24
Recipe To determine the
subnets, detach each interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet.
Subnet mask: /24
93
Configuration of IP address
DHCP
manual
4-94
IP Fragmentation & Reassembly network links have MTU
(max.transfer size) - largest possible link-level frame. different link types,
different MTUs large IP datagram divided
(“fragmented”) within net one datagram becomes
several datagrams “reassembled” only at
final destination IP header bits used to
identify, order related fragments
fragmentation: in: one large datagram
out: 3 smaller datagrams
reassembly
4-95
IP Fragmentation and Reassembly
ID=x
offset=0
fragflag=0
length=4000
ID=x
offset=0
fragflag=1
length=1500
ID=x
offset=185
fragflag=1
length=1500
ID=x
offset=370
fragflag=0
length=1040
One large datagram becomesseveral smaller datagrams
Example 4000 byte
datagram MTU = 1500
bytes
1480 bytes in data field
offset =1480/8
96
Fragmentation example (I)
Router>enableRouter#conf tRouter(config)#hostname Router1Router1(config)#interface ethernet 1Router1(config-if)#mtu 100Router1(config-if)#exitRouter1(config)#endRouter1#writeBuilding configuration...[OK]
Configuração do MTU do interface 1 do router 1
C:\>ping -l 300 12.0.0.2 Pinging 12.0.0.2 with 300 bytes of data: Reply from 12.0.0.2: bytes=300 time=223ms TTL=116Reply from 12.0.0.2: bytes=300 time=223ms TTL=116Reply from 12.0.0.2: bytes=300 time=223ms TTL=116Reply from 12.0.0.2: bytes=300 time=223ms TTL=116
Router1
10.0.0.0
10.0.0.2Default Gatew ay: 10.0.0.1
11.0.0.0
Router2
12.0.0.0
12.0.0.2Default Gatew ay:12.0.0.1
11.0.0.3
Eth0 Eth0Eth1 Eth1
10.0.0.1 11.0.0.1 11.0.0.2 12.0.0.1
97
Fragmentation example (II)
Packets captured in network 11.0.0.0
Router1
10.0.0.0
10.0.0.2Default Gatew ay: 10.0.0.1
11.0.0.0
Router2
12.0.0.0
12.0.0.2Default Gatew ay:12.0.0.1
11.0.0.3
Eth0 Eth0Eth1 Eth1
10.0.0.1 11.0.0.1 11.0.0.2 12.0.0.1
98
Fragmentation example (III)
Packet nº 1 captured in network 11.0.0.0
99
Fragmentation example (IV)
Packet nº 2 captured in network 11.0.0.0
100
Fragmentation example (V)
Packet nº 4 captured in network 11.0.0.0
101
From source to 1st router
When a node wants to send an IP datagram to a node that is in another subnet, it must send the datagram to the default gateway Configured by the user (or through DHCP) IP address of one of the routers of the source node’s subnet,
namely the IP address of the router interface attached to the subnet
Router
Router
origem
Router
destino
default gateway
4-102
ICMP: Internet Control Message Protocol
used by hosts & routers to communicate network-level information error reporting: unreachable host, network, port, protocol echo request/reply (used by ping)
network-layer “above” IP: ICMP msgs carried in IP datagrams
ICMP message: type, code plus first 8 bytes of IP datagram causing error
Type Code description0 0 echo reply (ping)3 0 dest. network unreachable3 1 dest host unreachable3 2 dest protocol unreachable3 3 dest port unreachable3 6 dest network unknown3 7 dest host unknown4 0 source quench (congestion control - not used)8 0 echo request (ping)9 0 route advertisement10 0 router discovery11 0 TTL expired12 0 bad IP header
4-103
ICM P
ICMP – Encapsulation
Fields common to all ICMP messages
type
code
checksum
1
1
2
cabeçalhoIP
dados IP
cabeçalhoMAC
dados MAC
104
Ping
The source sends a message of type Echo Request
The destination answers with a message of type Echo Reply
Tests (i) the protocol stack of the source up to ICMP (ii) the same for the receiver (iii) the connectivity between source and destination in both directions
Router
Echo Request
Echo Reply
Echo Request
Echo Reply
type = 0 ou 8
code = 0
checksum
identifier
sequence number
optional data
1
1
2
2
2
105
Ping optionsC:\>ping Usage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS] [-r count] [-s count] [[-j host-list] | [-k host-list]] [-w timeout] destination-list Options: -t Ping the specifed host until stopped. To see statistics and continue - type Control-Break; To stop - type Control-C. -a Resolve addresses to hostnames. -n count Number of echo requests to send. -l size Send buffer size. -f Set Don't Fragment flag in packet. -i TTL Time To Live. -v TOS Type Of Service. -r count Record route for count hops. -s count Timestamp for count hops. -j host-list Loose source route along host-list. -k host-list Strict source route along host-list. -w timeout Timeout in milliseconds to wait for each reply.
106
Ping example192.168.8.224
Router
192.168.8.0
192.168.8.1
Ping enviado pela estação:
C:\>ping 192.168.8.1 Pinging 192.168.8.1 with 32 bytes of data: Reply from 192.168.8.1: bytes=32 time<10ms TTL=126Reply from 192.168.8.1: bytes=32 time<10ms TTL=126Reply from 192.168.8.1: bytes=32 time<10ms TTL=126Reply from 192.168.8.1: bytes=32 time<10ms TTL=126
type = 0 ou 8
code = 0
checksum
identifier
sequence number
optional data
1
1
2
2
2
107
Traceroute
Discovers the routers in the path from source to destination Uses the TTL field and the ICMP time exceeded message
C:\>tracert Usage: tracert [-d] [-h maximum_hops] [-j host-list] [-w timeout] target_name Options: -d Do not resolve addresses to hostnames. -h maximum_hops Maximum number of hops to search for target. -j host-list Loose source route along host-list. -w timeout Wait timeout milliseconds for each reply.
Router
Router
Router
TTL = 1
ICM P tim e exceeded
TTL = 2
TTL = 3
TTL = 4
ICM P tim e exceeded
108
Traceroute exampleC:\>tracert -d 193.136.173.30
Tracing route to 193.136.173.30 over a maximum of 30 hops
1 <10 ms <10 ms <10 ms 193.136.92.1 2 <10 ms <10 ms <10 ms 193.137.172.254 3 <10 ms <10 ms <10 ms 193.136.173.30
Trace complete.
5-109
Link Layer: IntroductionSome terminology: hosts and routers are nodes 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 adjacent node over a link
5-110
Where is the link layer implemented?
in each and every host link layer implemented
in “adaptor” (aka network interface card NIC) Ethernet card, PCMCI
card, 802.11 card implements link,
physical layer attaches into host’s
system buses combination of
hardware, software, firmware
controller
physicaltransmission
cpu memory
host bus
(e.g., PCI)
network adaptercard
host schematic
applicationtransportnetwork
link
linkphysical
5-111
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
112
Local Area Networks (LANs)
Interconnect nodes that are relatively close through broadcast links
Many technologies Ethernet, Token Ring, 802.11, FDDI, …
LAN
ROUTER
Internet
ServidorWeb
estações
estações
113
Ethernet
The MAC protocol is in geral CSMA/CD Supports technologies with different transmission media
and transfer rate 10 Mb/s, 100 Mb/s, 1 Gb/s, 10 Gb/s Coaxial cable , twisted pair, optical fiber 10BASE5, 10BASE2, 10BASET, 100BASET, ...
Segments are interconnected through hubs or receivers
Repetidor
Router
5-114
LAN AddressesEach adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
5-115
LAN Address (more)
MAC address allocation administered by IEEE manufacturer buys portion of MAC address space
(to assure uniqueness) See http://standards.ieee.org/regauth/ for
obtaining addresses analogy: (a) MAC address: like Social Security Number (b) 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
116
Ethernet frame format Dois tipos de tramas: Ethernet II e 802.3 Endereços
Endereços IEEE (6 bytes) Se NIC recebe trama com endereço destino igual ao endereço do NIC
ou com endereço de broadcast (e.g. ARP Request), então envia trama ao módulo de software identificado no campo Protocol; caso contrário, NIC descarta trama
Protocol: indica o tipo de protocolo transportado na trama (IP, ARP, IPX, ...)
Length: comprimemto da trama (campo dados) LLC: vários campos incluindo tipo de protocolo Frame Check Sequence (FCS): usado para detecção de erros
destination source protocol data FCS
6 6 2 46 - 1500 4
destination source length FCS
6 6 2 43 - 1497 4
LLC data
3
Ethernet II
802.3
> 1500
1500
117
Encapsulation TFTP – the complete story
message
TFTPheader
TFTPmessage
buildsTFTP
header
message
TFTPheader
UDPheader
UDPdata
UDPsegment
buildsUDP
header calls IP
message
TFTPheader
UDPheader
IPheader
IPdata
IPdatagram
buildsIP
headercalls driver
Ethernet
message
TFTPheader
UDPheader
IPheader
Ethernetheader
Ethernetdata
Ethernetframe
buildsEthernet header
Sends bits to “the wire”
calls UDP
5-118
ARP: Address Resolution Protocol
Each IP node (host, router) on LAN has ARP table
ARP table: IP/MAC address mappings for some LAN nodes
< IP address; MAC address; TTL>
TTL (Time To Live): time after which address mapping will be forgotten (typically 20 min)
Question: how to determineMAC address of B
knowing B’s IP address?
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
137.196.7.23
137.196.7.78
137.196.7.14
137.196.7.88
5-119
ARP protocol: Same LAN (network) A wants to send
datagram to B, and B’s MAC address not in A’s ARP table.
A broadcasts ARP query packet, containing B's IP address dest MAC address =
FF-FF-FF-FF-FF-FF all machines on LAN
receive ARP query B receives ARP packet,
replies to A with its (B's) MAC address frame sent to A’s MAC
address (unicast)
A caches (saves) 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 ARP is “plug-and-play”:
nodes create their ARP tables without intervention from net administrator
120
ARP protocol
4.1.1.11500- 10- 4B- 4E- 74- 25
4.1.1.100- 60- 97- D4- 9F- A0
4.1.1.11500- 10- 4B- 4E- 74- 25
4.1.1.100- 60- 97- D4- 9F- A0
ARP Request
ARP Response
121
ARP Request
ARP Request enviado pela estação 4.1.1.115 para saber o endereço MAC da estação 4.1.1.1.
122
ARP Response
Resposta da estação 4.1.1.1 enviada através de ARP Response: o endereço MAC é 00-60-97-d4-9f-a0
123
ARP commandARP -a [inet_addr] [-N if_addr] -a Displays current ARP entries by interrogating the current protocol data. If inet_addr is specified, the IP and Physical addresses for only the specified computer are displayed. If more than one network interface uses ARP, entries for each ARP table are displayed. -g Same as -a. inet_addr Specifies an internet address. -N if_addr Displays the ARP entries for the network interface specified by if_addr. -d Deletes the host specified by inet_addr. -s Adds the host and associates the Internet address inet_addr with the Physical address eth_addr. The Physical address is given as 6 hexadecimal bytes separated by hyphens. The entry is permanent. eth_addr Specifies a physical address. if_addr If present, this specifies the Internet address of the interface whose address translation table should be modified. If not present, the first applicable interface will be used.Example: > arp -s 157.55.85.212 00-aa-00-62-c6-09 .... Adds a static entry. > arp -a .... Displays the arp table.
124
ARP example
Estação A192.168.8.224
Estação B192.168.8.220
192.168.8.0
C:\>arp -a Interface: 192.168.8.224 on Interface 0x1000002 Internet Address Physical Address Type 192.168.8.220 00-60-97-d4-9f-a0 dynamic
1º ping
2º ping
3º ping
C:\>arp -d 192.168.8.220C:\>arp -aNo ARP Entries Found
5-125
Addressing: routing to another LAN
R
1A-23-F9-CD-06-9B
222.222.222.220111.111.111.110
E6-E9-00-17-BB-4B
CC-49-DE-D0-AB-7D
111.111.111.112
111.111.111.111
A74-29-9C-E8-FF-55
222.222.222.221
88-B2-2F-54-1A-0F
B222.222.222.222
49-BD-D2-C7-56-2A
walkthrough: send datagram from A to B via R assume A knows B’s IP address
two ARP tables in router R, one for each IP network (LAN)
5-126
A creates IP datagram with source A, destination B A uses ARP to get R’s MAC address for 111.111.111.110 A creates link-layer frame with R's MAC address as dest,
frame contains A-to-B IP datagram A’s NIC sends frame R’s NIC receives frame R removes IP datagram from Ethernet frame, sees its
destined to B R uses ARP to get B’s MAC address R creates frame containing A-to-B IP datagram sends to
B
R
1A-23-F9-CD-06-9B
222.222.222.220
111.111.111.110
E6-E9-00-17-BB-4B
CC-49-DE-D0-AB-7D
111.111.111.112
111.111.111.111
A74-29-9C-E8-FF-55
222.222.222.221
88-B2-2F-54-1A-0F
B222.222.222.222
49-BD-D2-C7-56-2A
This is a really importantexample – make sure you
understand!
127
Routing from A to B
Host A verifies that B is on its subnet, when applying mask 255.255.255.0 to 223.1.2.2
Does ARP to 223.1.2.2, if required
Sends datagram to B, encapsulated in MAC frame
MAC dest addr = MAC of B
223.1.2.6
223.1.2.1 223.1.2.2
223.1.8.1 223.1.8.2
223.1.3.27
223.1.3.1 223.1.3.2
223.1.9.1
223.1.9.2
223.1.1.3
223.1.1.1 223.1.1.2 223.1.1.4
223.1.7.1
223.1.7.5
223.1.7.3
A B
C
223.1.1.0/24
223.1.8.0/24
223.1.3.0/24223.1.2.0/24
223.1.9.0/24223.1.7.0/24
i1i2
i3
i1i2
i3
i1 i2
i3
R1 R2
R3
MAC heade
r
several IP 223.1.2.1 data223.1.2.2
128
Routing from A to C
Initially... Host A verifies that C is on
another subnet, when applying mask 255.255.255.0 to 223.1.1.4
Does ARP to the default gateway (223.1.2.6), if required
Sends datagram to R1, encapsulated in MAC frame
MAC dest addr = MAC of 223.1.2.6
223.1.2.6
223.1.2.1 223.1.2.2
223.1.8.1 223.1.8.2
223.1.3.27
223.1.3.1 223.1.3.2
223.1.9.1
223.1.9.2
223.1.1.3
223.1.1.1 223.1.1.2 223.1.1.4
223.1.7.1
223.1.7.5
223.1.7.3
A B
C
223.1.1.0/24
223.1.8.0/24
223.1.3.0/24223.1.2.0/24
223.1.9.0/24223.1.7.0/24
i1i2
i3
i1i2
i3
i1 i2
i3
R1 R2
R3
MAC heade
r
several IP 223.1.2.1 data223.1.1.4
129
Routing from A to C
223.1.1.0/24
223.1.2.0/24
Subnet
223.1.8.2
direct
Next hop
i2
i1
Interface
223.1.3.0/24
223.1.7.0/24
223.1.8.2
223.1.8.2
i2
i2
223.1.8.0/24 direct i2
223.1.9.0/24 direct i3
When datagram arrives at R1...
Search routing table Interface = i2 Next hop = 223.1.8.2
Send datagram to R2 via i2, encapsulated in PPP frame
223.1.2.6
223.1.2.1 223.1.2.2
223.1.8.1 223.1.8.2
223.1.3.27
223.1.3.1 223.1.3.2
223.1.9.1
223.1.9.2
223.1.1.3
223.1.1.1 223.1.1.2 223.1.1.4
223.1.7.1
223.1.7.5
223.1.7.3
A B
C
223.1.1.0/24
223.1.8.0/24
223.1.3.0/24223.1.2.0/24
223.1.9.0/24223.1.7.0/24
i1i2
i3
i1i2
i3
i1 i2
i3
R1 R2
R3
Routing table of R1
PPP heade
r
several IP 223.1.2.1 data223.1.1.4
130
Routing from A to C
223.1.1.0/24
223.1.2.0/24
Subnet
223.1.7.3
223.1.8.1
Next hop
i3
i2
Interface
223.1.3.0/24
223.1.7.0/24
direct
direct
i1
i3
223.1.8.0/24 direct i2
223.1.9.0/24 223.1.7.3 i3
When datagram arrives at R2... Search routing table
Interface = i3 Next hop = 223.1.7.3
Does ARP to 223.1.7.3, if required
Sends datagram to R3 via i3, encapsulated in MAC frame
MAC dest addr = MAC of 223.1.7.3
223.1.2.6
223.1.2.1 223.1.2.2
223.1.8.1 223.1.8.2
223.1.3.27
223.1.3.1 223.1.3.2
223.1.9.1
223.1.9.2
223.1.1.3
223.1.1.1 223.1.1.2 223.1.1.4
223.1.7.1
223.1.7.5
223.1.7.3
A B
C
223.1.1.0/24
223.1.8.0/24
223.1.3.0/24223.1.2.0/24
223.1.9.0/24223.1.7.0/24
i1i2
i3
i1i2
i3
i1 i2
i3
R1 R2
R3
Routing table of R2
MAC heade
r
severalIP 223.1.2.1 223.1.1.4 data
131
Routing from A to C
223.1.1.0/24
223.1.2.0/24
Rede
direct
223.1.9.1
Next hop
i3
i1
Interface
223.1.3.0/24
223.1.7.0/24
223.1.7.1
direct
i2
i2
223.1.8.0/24 223.1.7.1 i2
223.1.9.0/24 direct i1
When datagram arrives at R3... Search routing table
Interface = i3 Next hop = directo
Does ARP to 223.1.1.4, if required
Sends datagram to C via i3, encapsulated in MAC frame
MAC dest addr = MAC of 223.1.1.4
223.1.2.6
223.1.2.1 223.1.2.2
223.1.8.1 223.1.8.2
223.1.3.27
223.1.3.1 223.1.3.2
223.1.9.1
223.1.9.2
223.1.1.3
223.1.1.1 223.1.1.2 223.1.1.4
223.1.7.1
223.1.7.5
223.1.7.3
A B
C
223.1.1.0/24
223.1.8.0/24
223.1.3.0/24223.1.2.0/24
223.1.9.0/24223.1.7.0/24
i1i2
i3
i1i2
i3
i1 i2
i3
R1 R2
R3
Routing table of R3
MAC heade
r
several IP 223.1.2.1 223.1.1.4 data
132
Bibliography
James Kurose, Keith Ross, “Computer Networking – A Top-Down Approach”, 4th edition, 2007, Addison Wesley Chapter 1 – “Computer Networks and the Internet” Section 4.1 – “Introduction” Section 4.4 – “The Internet Protocol (IP): Forwarding and
Addressing in the Internet” Section 5.1 – “Link Layer: Introduction and Services” Section 5.4 – “Link-Layer Addressing” Section 5.5 – “Ethernet”
