telecommunication network models

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2.1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


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22--1 LAYERED TASKS1 LAYERED TASKS

WeWe useuse thethe conceptconcept ofof layerslayers inin ourour dailydaily lifelife.. AsAs anan

exam leexam le letlet usus considerconsider twotwo riendsriends whowho communicatecommunicate

throughthrough postalpostal mailmail.. TheThe processprocess ofof sendingsending aa letterletter toto aafriendfriend wouldwould bebe complexcomplex ifif therethere werewere nono servicesservices

availableavailable fromfrom thethe postpost officeoffice..

To ics discussed in this section:To ics discussed in this section:

Sender, Receiver, and Carrier

Hierarchy

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Figure 2.1 Tasks involved in sending a letter

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22--2 THE OSI MODEL2 THE OSI MODEL

EstablishedEstablished inin 19471947,, thethe InternationalInternational StandardsStandards

OrganizationOrganization ((ISOISO)) isis aa multinationalmultinational bodybody dedicateddedicated toto

..

standardstandard thatthat coverscovers allall aspectsaspects ofof networknetwork

((OSIOSI)) modelmodel.. ItIt waswas firstfirst introducedintroduced inin thethe latelate 19701970ss..

To ics discussed in this section:To ics discussed in this section:

Layered Architecture

Peer-to-Peer Processes

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ncapsu a on


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Note

ISO is the organization.

OSI is the model.

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Figure 2.2 Seven layers of the OSI model

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Figure 2.3 The interaction between layers in the OSI model

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Figure 2.4 An exchange using the OSI model

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22--3 LAYERS IN THE OSI MODEL3 LAYERS IN THE OSI MODEL

InIn thisthis sectionsection wewe brieflybriefly describedescribe thethe functionsfunctions ofof eacheach

layerlayer inin thethe OSIOSI modelmodel..

Physical Layer

Topics discussed in this section:Topics discussed in this section:

Network Layer

Transport Layer

ess on LayerPresentation Layer

A lication La er

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Figure 2.5 Physical layer

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Note

The physical layer is responsible for movements of

individual bits from one hop (node) to the next.

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Figure 2.6 Data link layer

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Note

The data link layer is responsible for moving

frames from one hop (node) to the next.

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Figure 2.7 Hop-to-hop delivery

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Figure 2.8 Network layer

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Note

The network layer is responsible for the

delivery of individual packets fromthe source host to the destination host.

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Figure 2.9 Source-to-destination delivery

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Figure 2.10 Transport layer

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Note

The transport layer is responsible for the delivery

of a message from one process to another.

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Figure 2.11 Reliable process-to-process delivery of a message

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Figure 2.12 Session layer

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Note

The session layer is responsible for dialog

control and synchronization.

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Figure 2.13 Presentation layer

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Note

The presentation layer is responsible for translation,

compression, and encryption.

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Figure 2.14 Application layer

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Note

The application layer is responsible for

providing services to the user.

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Figure 2.15 Summary of layers

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22--4 TCP/IP PROTOCOL SUITE4 TCP/IP PROTOCOL SUITE

TheThe layerslayers inin thetheTCP/IPTCP/IP protocolprotocol suitesuitedodo notnot exactlyexactly

matchmatch thosethose inin thethe OSIOSI modelmodel.. TheThe originaloriginal TCP/IPTCP/IP

protocolprotocol suitesuite waswas defineddefined asas havinghaving fourfour layerslayers::hosthost--toto--

networknetwork,, internetinternet,, transporttransport,, andandapplicationapplication.. However,However,

,,

TCP/IPTCP/IP protocolprotocol suitesuite isis mademade ofof fivefive layerslayers:: physicalphysical,,

Topics discussed in this section:Topics discussed in this section:

Physical and Data Link LayersNetwork Layer

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Application Layer


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Figure 2.16 TCP/IP and OSI model

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22--5 ADDRESSING5 ADDRESSING

FourFour levelslevels ofof addressesaddresses areare usedused inin anan internetinternet employingemploying

thethe TCP/IPTCP/IP protocolsprotocols::physicalphysical,,logicallogical,,portport,, andand pecificpecific..

Topics discussed in this section:Topics discussed in this section:Physical Addresses

Logical Addresses

Specific Addresses

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Figure 2.17 Addresses in TCP/IP

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Figure 2.18 Relationship of layers and addresses in TCP/IP

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Example 2.1

In Figure 2.19 a node with physical address 10 sends a

frame to a node with physical address 87. The two nodes

are connected by a link (bus topology LAN). As the

gure ows, e compu er w p ys ca a ress s

the sender, and the computer with physical address87is

.

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Figure 2.19 Physical addresses

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Example 2.2

As we will see in Chapter 13, most local-area networks

use a 48-bit (6-byte) physical address written as 12

hexadecimal digits; every byte (2 hexadecimal digits) is

epara e y a co on, as own e ow:

: : : : :

- y e exa ec ma g s p ys ca a ress.

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Example 2.3

i ure 2.20 hows a art o an internet with two routers

connecting three LANs. Each device (computer orrouter) has a pair of addresses (logical and physical) for

each connection. In this case, each computer is

connected to only one link and therefore has only one

. , ,

three networks (only two are shown in the figure). So

each outer has three airs o ddresses one or each

connection.

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Figure 2.20 IP addresses

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Example 2.4

Figure 2.21 shows two computers communicating via the

nternet. e en ng computer s runn ng t ree

processes at this time with port addresses a, b, and c. The

with port addresses j and k. Process a in the sending

com uter needs to communicate with rocess in thereceiving computer. Note that although physical

addresses change from hop to hop, logical and port

addresses remain the ame from the ource todestination.

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Figure 2.21 Port addresses

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Note

The physical addresses will change from hop to hop,

but the logical addresses usually remain the same.

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Example 2.5

As we will see in Chapter 23, a port address is a 16-bit

address represented by one decimal number as hown.

753

A 16-bit port address represented

as one single number.

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Note

The physical addresses change from hop to hop,

but the logical and port addresses usually remain the same.

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telecommunication network models

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