The OSI Sharad

8/9/2019 The OSI Sharad

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OSI MODELOSI MODELPresented byPresented by

SHARAD SINHASHARAD SINHA


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What is theWhat is the

OSI Reference Model?OSI Reference Model?

It is a conceptualIt is a conceptual

framework specifyingframework specifyingthe networkthe networkfunctions that occurfunctions that occurat each layerat each layer

It is a way ofIt is a way ofpicturing howpicturing howinformation travelsinformation travelsthrough networks.through networks.


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Who made up the OSI?Who made up the OSI?

It was created by theIt was created by theInternational OrganizationInternational Organizationfor Standardization (ISO).for Standardization (ISO).Term open denotes theTerm open denotes theability to connectany twoability to connectany twosystems which conform tosystems which conform to

the reference model

andt

he reference model

andassociated standards.associated standards.


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Tasks involved in sending letterTasks involved in sending letter


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To accomplish this task data must travel fromTo accomplish this task data must travel fromthe application layer to the physical layer onthe application layer to the physical layer onone computer across the network mediaandone computer across the network mediaandfrom the physical layer to the applicationfrom the physical layer to the applicationlayer ofanother computerlayer ofanother computer

Computer A Computer B


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7 Layers7 Layers

77.. Application LayerApplication Layer

6.6. Presentation LayerPresentation Layer

5.5. Session LayerSession Layer

4.4. Transport LayerTransport Layer

3.3. Network LayerNetwork Layer

2.2. Data Link LayerData Link Layer

1.1. Physical LayerPhysical Layer

All

People

SeemTo

Need

DataProcessing


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Interfaces between LayersInterfaces between Layers

There is anThere is an interfaceinterface between each pair ofadjacentbetween each pair ofadjacentlayers.layers.

This interface defines what information and services aThis interface defines what information and services alayer must provide for the layer above it.layer must provide for the layer above it.


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Physical Layer

Physical LayerProvidesProvides physicalphysical interf aceinterface forfor transmissiontransmission of of

informationinformation..

DefinesDefines rulesrules byby whichwhich bitsbits areare passedpassed fromfrom oneone systemsystem

toto anotheranother onon aa physicalphysical communicationcommunication mediummedium..

CoversCovers allall -- mechanical,mechanical, electrical,electrical, functionalfunctional andandproceduralprocedural -- aspectsaspects forfor physicalphysical communicationcommunication..

SuchSuch characteristicscharacteristics asas volt agevoltage levels,levels, timingtiming ofof voltagevoltagechanges,changes, physicalphysical datadata rates,rates, maximummaximum transmissiontransmissiondistances,distances, physicalphysical connectors,connectors, andand ot herother similarsimilarattributesattributes areare defineddefined byby physicalphysical layerlayer specificationsspecifications..

OSI Model


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Data Link LayerData Link LayerDataData linklink layerlayer attemptsattempts toto provideprovide reliablereliablecommunicationcommunication overover thethe physicalphysical layerlayer interfaceinterface..

BreaksBreaks thethe outgoingoutgoing datadata intointo framesframes andand reassemblereassemble

thethe receivedreceived framesframes..CreateCreate andand detectdetect frameframe boundariesboundaries..HandleHandle errorserrors byby implementingimplementing anan acknowledgementacknowledgementandand retransmissionretransmission schemescheme..ImplementImplement flowflow controlcontrol..

SupportsSupports pointspoints--toto--pointpoint asas wellwell asas broadcastbroadcastcommunicationcommunication..SupportsSupports simplex,simplex, halfhalf--duplexduplex oror fullfull--duplexduplexcommunicationcommunication..

OSI Model


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Network Layer

Network LayerImplementsImplements routingrouting ofof framesframes (packets)(packets) t hroughthrough thethe

networknetwork..

DefinesDefines th

eth

e mostmost optimumoptimum pa

th

pa

th

th

eth

e pa

cketpa

cket sh

ouldsh

ould ta

keta

kefromfrom thethe sourcesource toto thethe destinationdestination..

DefinesDefines logicallogical addressingaddressing soso thatthat anyany endpointendpoint cancan bebeidentifiedidentified..

HandlesHandles congestioncongestion inin thethe networknetwork..

OSI Model


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Transport Layer

Transport LayerPurposePurpose ofof thisthis layerlayer isis toto provideprovide aa reliablereliable mechanismmechanism

forfor t hethe exchangeexchange of of datadata betweenbetween twotwo processesprocesses inindifferentdifferent computerscomputers..

EnsuresEnsures thatthat thethe datadata unitsunits areare delivereddelivered errorerror freefree..

EnsuresEnsures thatthat datadata unitsunits areare delivereddelivered inin sequencesequence..

EnsuresEnsures thatthat therethere isis nono lossloss oror duplicationduplication ofof datadata unitsunits..

ProvidesProvides connectionlessconnectionless oror connectionconnection orientedoriented serviceservice..ProvidesProvides forfor t hethe connectionconnection managementmanagement..

MultiplexMultiplex multiplemultiple connectionconnection overover aa singlesingle channelchannel..

OSI Model


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Session LayerSession LayerSessionSession layerlayer providesprovides mechanismmechanism forfor controllingcontrolling thethe dialoguedialoguebetweenbetween thethe twotwo endend systemssystems.. ItIt definesdefines howhow toto start,start, controlcontrolandand endend conversationsconversations (called(called sessions)sessions) betweenbetweenapplicationsapplications..

ThisThis layerlayer requestsrequests forfor aa logicallogical connectionconnection toto bebe establishedestablishedonon anan endend--usersusers requestrequest..AnyAny necessarynecessary loglog--onon oror passwordpassword validationvalidation isis alsoalso handledhandledbyby thisthis layerlayer..SessionSession layerlayer isis alsoalso responsibleresponsible forfor terminatingterminating t hethe

connectionconnection..SessionSession layerlayer cancan alsoalso provideprovide checkcheck--pointingpointing mechanismmechanismsuchsuch thatthat ifif aa failurefailure of of somesome sort sort occursoccurs betweenbetweencheckpoints,checkpoints, allall datadata cancan bebe retransmittedretransmitted fromfrom t hethe lastlastcheckpointcheckpoint..

OSI Model


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Presentation Layer

Presentation LayerPresentationPresentation layerlayer definesdefines thethe formatformat inin whichwhich thethe datadata isis

toto bebe exchangedexchanged betweenbetween t hethe twotwo communicatingcommunicatingentitiesentities..

AlsoAlso handleshandles datadata compressioncompression andand datadata encryptionencryption

(cryptography)(cryptography)..

OSI Model


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Application Layer

Application LayerApplicationApplication layerlayer interactsinteracts withwith applicationapplication programsprograms andand

isis thethe highesthighest levellevel ofof OSIOSI modelmodel..

ApplicationApplication layerlayer cont ainscontains managementmanagement functionsfunctions totosupportsupport distributeddistributed applicationsapplications..

ExamplesExamples ofof applicationapplication layerlayer areare applicationsapplications suchsuch asasfilefile transfer,transfer, electronicelectronic mail,mail, remoteremote loginlogin etcetc..

OSI Model


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OSI Reference ModelOSI Reference Model

Host Layers:

}Media Layers:

}Control physical delivery of

messages over a network

Provide accurate data

delivery between computers


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DEVICES IN THE LAYERSDEVICES IN THE LAYERS

HUBHUB--LAYER 2LAYER 2

SWITCHSWITCH--LAYER 2LAYER 2

BRIDGEBRIDGE--LAYER 2LAYER 2 ROUTERROUTER--LAYER 3LAYER 3

BROUTERBROUTER--LAYER 3LAYER 3

GATEWAYGATEWAY--ALL LAYERS 1 TO 7ALL LAYERS 1 TO 7


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PACKET DRAWINGPACKET DRAWING


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As data moves down through theAs data moves down through thelayers of the OSI model, headers arelayers of the OSI model, headers are

added.added.Computer A


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Computer B

As data moves up through the layersAs data moves up through the layersof the OSI model, headers areof the OSI model, headers are

removed.removed.


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Thank youThank you

THANK YOUTHANK YOU

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