The OSI Model and the TCP/IP Protocol Suite 1 Example 1 Assum - - PowerPoint PPT Presentation

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The OSI Model and the TCP/IP Protocol Suite 1 Example 1 Assum - - PowerPoint PPT Presentation

Nov 09, 2022 5.02k likes •5.67k views

The OSI Model and the TCP/IP Protocol Suite 1 Example 1 Assum Assume Mar aria ia an and Ann are are nei neighb hbors ors wi with th a lo lot of of comm common ideas eas. Howev However, er, Mar Maria ia sp speaks eaks only ly

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The OSI Model and the TCP/IP Protocol Suite

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Assum Assume Mar aria ia an and Ann are are nei neighb hbors

  • rs wi

with th a lo lot of

  • f comm

common ideas

  • eas. Howev

However, er, Mar Maria ia sp speaks eaks only ly Sp Spanish ish, and and Ann nn spea speaks ks

  • nly

ly En Engli lish

  • sh. Sin

ince both both hav have le learn arned ed the the sign sign la langu guage age in in their their ch childho ldhood,

  • d, they

they en enjo joy meetin meeting in in a cafe cafe a coupl couple of

  • f days

days per per we week ek and and exc excha hang nge the their ir ide deas as us using ng signs

  • signs. Occasiona

Occasionall lly, y, they they als lso use use a bili iling ngua ual dict dictionary

  • ionary. Com

Commun munica icati tion

  • n is

is face face to to face face and and Ha Happens in in one

  • ne layer as

as shown wn in in the followi wing ng Figure re.

Example 1

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3

No Now assume assume that that An Ann has has to to mov

  • ve to

to ano another ther tow town bec ecaus ause of

  • f

her er job

  • job. Be

Before fore she she mov moves, es, the the two two meet meet for for the the la last st time time in in the the sam same cafe

  • cafe. Al

Alth thou

  • ugh

gh both

  • th are

are sad, d, Mar Maria sur surprises prises Ann nn whe when sh she opens

  • pens a packet

acket th that at contains contains tw two smal small mac machines

  • hines. The

The first first mac machine hine can scan scan and and tran transform sform a let etter ter in in Eng Engli lish to to a secret secret co code de or

  • r vice

vice versa

  • versa. Th

The other

  • ther mach

machine ne can can sca can and and tr trans nslate ate a lett etter er in in Span Spanis ish to to the the same same secr ecret et code code or

  • r vice

vice versa

  • versa. An

Ann takes takes the the first first mach machin ine; Mar Maria ia keeps eps the the sec econ

  • nd on
  • ne. The

The two two fr friends iends can can sti till commun communica icate te using using the the sec secret ret code, code, as as shown shown in in Figure.

Example 2

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4

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Topics Discussed in the Section

Hierarchy Layer 0: Tranport the letter Layer 1: drop in the mailbox Layer 2: Translate to secret code Layer 3: Write letter Services Sender site: uses the services of the layer below it Receiver site: provide service to the layer above it

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THE OSI MODEL

Es Estab tablis lishe hed in in 19 1947, the the Int Inter erna nation tional al Sta Stand ndar ards ds Or Organ ganiza izatio tion (I (ISO) SO) is is a multi multinat nation ional al body body ded dedica icated ted to to wor world ldwide wide ag agre reem emen ent on

  • n in

inter ternati ational

  • nal st

stan anda dards ds. Al Almos most thr hree ee-fou fourth rths of

  • f co

coun untri tries es in in the the worl world are re re repre prese sente nted in in the the ISO

  • SO. An

An ISO SO sta standa ndard rd tha that cover covers al all as aspe pect cts of

  • f ne

networ twork co comm mmun unic icati ation

  • ns is

is the the Open Systems Interconnection (OSI) mod model

  • el. It

It was as first first intro rodu duce ced in in the late 1970 1970s.

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The OSI model

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OSI layers

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Layered Architecture

Organization of the layers Layer 1,2,3 --- network support layers Layer 5,6,7 --- user support layers Layer 4 --- link the two subgroups and ensure the

format is compatible.

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An exchange using the OSI model

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Layered Architecture

Encapsulation: The data part of a package at level N is carrying

the whole packet (data + overhead) from level N+1

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Physical Layer

Physical characteristics of interfaces and media Representation of bits Data rate Synchronization of bits Line configuration Physical topology Mesh topology; star topology; ring topology; bus

topology

Transmission mode Simplex mode; half-duplex mode; full-duplex mode

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The physical layer is responsible for moving individual bits from one (node) to the next.

Note

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Data Link Layer

Framing Physical addressing Flow control Error control Access control

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Network Layer

Logical addressing Routing

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Transport Layer

Service-point addressing Segmentation and reassembly Connection control Flow control Error control

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Session Layer

Dialog control Synchronization

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Presentation Layer

Translation Encryption Compression

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Application Layer

Network virtual terminal File transfer, access, and management (FTAM) E-mail services Directory services

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Summary of OSI Layers

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TCP/IP PROTOCOL SUITE

Th The TC TCP/IP P/IP pr protoco

  • tocol su

suite ite was as deve develo loped ed pr prior

  • r to

to the the OSI OSI mode

  • del. The

Theref refore

  • re, the

the lay layers ers in in the the TC TCP/I P/IP pr proto

  • toco

col su suite ite do do not not match match ex exac actly tly with ith tho those se in in the the OSI SI mod model

  • el. The

The origi

  • rigina

nal TCP TCP/IP /IP pr proto

  • toco

col suite suite was was def define ined as as fou four so software ftware lay layers ers bui built lt upon upon th the ha hard rdwar

  • are. Toda

Today, y, ho howev wever er, TCP/IP TCP/IP is is tho thoug ught ht of

  • f as

as a fiv five-la layer yer mod

  • del

el with ith the the lay ayer ers na named ed si simila milarly rly to to the ones

  • nes in

in the OSI SI model.

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TCP/IP and OSI model

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A private internet

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Communication at the physical layer

A Physical layer Physical layer

R1 R3 R4

B

Source Destination

Legend 011 ... 101 011 ... 101 011 ... 101 011 ... 101 Link 3 Link 5 Link 6 Link 1

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The unit of communication at the physical layer is a bit.

Note

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Communication at the data link layer

A

Physical Physical Data link Data link R1 R3 R4

B

Source Destination Data D Header H

Legend Link 1 Link 3 Link 5 Link 6 Frame D2 H2 F r a m e D 2 H 2 Frame D2 H2 Frame D2 H2

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The unit of communication at the data link layer is a frame.

Note

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Communication at the network layer

A

Physical Physical Data link Data link R1 R3 R4

B

Network Network Source Destination Data D Header H

Legend Datagram D3 H3 Datagram D3 H3

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The unit of communication at the network layer is a datagram.

Note

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Communication at transport layer

A

Physical Physical Data link Data link R1 R3 R4

B

Network Network Transport Transport Source Destination Data D Header H

Legend Segment D4 H4 Segment D4 H4

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The unit of communication at the transport layer is a segment, user datagram, or a packet, depending on the specific protocol used in this layer.

Note

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Communication at application layer

A

Physical Physical Data link Data link R1 R3 R4

B

Network Network Transport Transport Application Application Source Destination Data D Header H

Legend Message D5 D5 D5 D5 Message

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The unit of communication at the application layer is a message.

Note

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ADDRESSING

Fo Four ur le levels vels of

  • f addr

addres esse ses ar are used used in in an an inter interne net employ mploying ing the the TC TCP/I P/IP pro protoc tocols

  • ls: phy

physic sical al add addres ress, s, lo logic ical al add addre ress ss, po port rt address, address, and and ap appl plic icati ation

  • n-

sp spec ecifi ific add addre ress

  • ss. Ea

Each ch ad addr dres ess is is re relate ated to to a one

  • ne

layer er in in the TC TCP/ P/IP archit hitec ecture re.

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Addresses in the TCP/IP protocol suite

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physical addresses

Data 87 10 1

packet accepted

Data 87 10 4

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logical addresses

Data A P 20 10 Data A P 20 10

Physical addresses changed

Data A P 33 99 Data A P 33 99

Physical addresses changed

Data A P 95 66 Data A P 95 66

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The physical addresses will change from hop to hop, but the logical addresses remain the same.

Note

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39 A Sender Receiver P

Internet

port numbers

a Data j A P H2 a Data j A P a Data j Data a Data j A P H2 a Data j A P a Data j Data

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The physical addresses change from hop to hop, but the logical and port addresses usually remain the same.

Note

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CONNECTING DEVICES

LANs ANs or

  • r WANs

ANs do do not not no norma rmally lly op

  • per

erate ate in in isola isolatio tion. Th They ey are are co conne nnecte cted to to one

  • ne ano

anothe ther or

  • r to

to the the Int Inter erne

  • net. To

To connect connect LANs ANs an and WANs ANs tog togeth ether we we use use co conn nnec ectin ting de devi vice

  • ces. Con
  • nnec

ecting ting de devi vices ces can can

  • p
  • per

erate ate in in di diffe ffere rent nt la laye yers rs of

  • f the

the Int Intern ernet et mod model

  • el. We

We di disc scus uss thr hree ee ki kind nds of

  • f co

connec nnectin ting de devi vice ces: re repeate peaters rs (or (or hubs), hubs), br brid idge ges (or (or two wo-lay ayer er swit switch ches es), ), and and router ters (or (or three ee-la laye yer switc tche hes) s).

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Topics Discussed in the Section

Repeaters (hubs) Bridges (two-layer switches) Routers (three-layer switches)

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Connecting devices

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Repeater or hub

Sent

Maintained

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A repeater forwards every bit; it has no filtering capability.

Note

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Bridge

71:2B:13:45:61:41 1 4 3 2 71:2B:13:45:61:42 64:2B:13:45:61:12 64:2B:13:45:61:13 Address Port Bridge table

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Learning bridge

  • a. Original

Address Port

  • c. After D sends a frame to B

71:2B:13:45:61:41 1 4 64:2B:13:45:61:13 Address Port

  • d. After B sends a frame to A

71:2B:13:45:61:41 1 4 2 71:2B:13:45:61:42 64:2B:13:45:61:13 Address Port

  • e. After C sends a frame to D

71:2B:13:45:61:41 1 4 3 2 71:2B:13:45:61:42 64:2B:13:45:61:12 64:2B:13:45:61:13 Address Port M M M M

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A bridge has a table used in filtering decisions.

Note

A bridge does not change the physical (MAC) addresses in a frame.

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Routers (three-layer switches) Can connect LANs and WANs together Has a physical and logical (IP) address for each of

its interfaces

Act only on the destination Change the physical address of the package (both

source and destination) when it forwards the packet

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Routing example

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A router is a three-layer (physical, data link, and network) device.

Note

A router changes the physical addresses in a packet.

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A repeater or a bridge connects segments of a LAN. A router connects independent LANs or WANs to create an internetwork (internet).

Note