computer network jhvjhjhbjn jhjbnbjkh .pdf

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1. Dr. B. C. Roy Engineering College
Student Name:-Subhadip Sinha
Student University Roll Number:-12030822004
Paper Name:-Computer Networks
Paper Code:-PCC-CS602
Topic:-OSI Model: The Backbone of Modern Networking
Department of Computer Science and Engineering (Artificial Intelligence and
Machine Learning)

2. Introduction to OSI Model
TheOSI(OpenSystemsInterconnection)Modelisasetofrulesthatexplainshow
differentcomputersystemscommunicateoveranetwork.
OSIModelwasdevelopedbytheInternationalOrganizationforStandardization
(ISO).
TheOSIModelconsistsof7layersandeachlayerhasspecificfunctionsand
responsibilities.Thislayeredapproachmakesiteasierfordifferentdevicesand
technologiestoworktogether.
OSIModelprovidesaclearstructurefordatatransmissionandmanaging
networkissues.
TheOSIModeliswidelyusedasareferencetounderstandhownetworksystems
function.

3. Layers of the OSI Model
There are 7 layers in the OSI Model and each layer has its specific role in handling
data. All the layers are mentioned below:-
1)Physical Layer
2)Data Link Layer
3)Network Layer
4)Transport Layer
5)Session Layer
6)Presentation Layer
7)Application Layer

4. Layer 1 –Physical Layer
ThelowestlayeroftheOSIreferencemodelisthePhysicalLayer.Itisresponsible
fortheactualphysicalconnectionbetweenthedevices.
Thephysicallayercontainsinformationintheformofbits.
PhysicalLayerisresponsiblefortransmittingindividualbitsfromonenodetothe
next.Whenreceivingdata,thislayerwillgetthesignalreceivedandconvertit
into0sand1sandsendthemtotheDataLinklayer,whichwillputtheframe
backtogether.Common physicallayerdevicesareHub,Repeater,Modem,
andCables.
Fig(1)

5. Layer 2 –Data Link Layer (DLL)
Thedatalinklayerisresponsibleforthenode-to-nodedeliveryofthemessage.
Themainfunctionofthislayeristomakesuredatatransferiserror-freefromone
nodetoanother,overthephysicallayer.Whenapacketarrivesinanetwork,it
istheresponsibilityoftheDLLtotransmitittotheHostusingitsMACaddress.
PacketintheDataLinklayerisreferredtoasFrame.SwitchesandBridgesare
commonDataLinkLayerdevices.

6. Layer 3 –Network Layer
Thenetworklayerworksforthetransmissionofdatafromonehosttotheother
locatedindifferentnetworks.Italsotakescareofpacketroutingi.e.selectionof
theshortestpathtotransmitthepacket,fromthenumberofroutesavailable.
Thesenderandreceiver’sIPaddressareplacedintheheaderbythenetwork
layer.SegmentintheNetworklayerisreferredtoasPacket.
Networklayerisimplementedbynetworkingdevicessuchasroutersand
switches.

7. Layer 4 –Transport Layer
Thetransportlayerprovidesservicestotheapplicationlayerandtakesservices
fromthenetworklayer.Thedatainthetransportlayerisreferredto
asSegments.Itisresponsiblefortheend-to-enddeliveryofthecomplete
message.
Thetransportlayeralsoprovidestheacknowledgment ofthesuccessfuldata
transmissionandre-transmitsthedataifanerrorisfound.Protocolsusedin
TransportLayerareTCP,UDPNetBIOS,PPTP.
Atthesender’sside,thetransportlayerreceivestheformatteddatafromthe
upperlayers,performsSegmentation,andalsoimplementsFlowanderror
controltoensureproperdatatransmission.ItalsoaddsSourceand
Destinationportnumberinitsheaderandforwardsthesegmenteddatatothe
NetworkLayer.

8. Layer 5 –Session Layer
SessionLayerintheOSIModelisresponsiblefortheestablishmentof
connections,management ofconnections,terminationsofsessionsbetween
twodevices.Italsoprovidesauthenticationandsecurity.Protocolsusedinthe
SessionLayerareNetBIOS,PPTP.
Letusconsiderascenariowhereauserwantstosendamessagethrough
someMessengerapplicationrunningintheirbrowser.The“Messenger”here
actsastheapplicationlayerwhichprovidestheuserwithaninterfaceto
createthedata.Thismessageorso-calledDataiscompressed,optionally
encrypted(ifthedataissensitive),andconvertedintobits(0’sand1’s)sothat
itcanbetransmitted.

9. Layer 6 –Presentation Layer
The presentation layer is also called theTranslation layer. The data from the
application layer is extracted here and manipulated as per the required format
to transmit over the network.
Protocols used in the Presentation Layer areJPEG,MPEG,GIF,TLS/SSL, etc.

10. Layer 7 –Application Layer
AttheverytopoftheOSIReferenceModelstackoflayers,wefindthe
Applicationlayerwhichisimplementedbythenetworkapplications.These
applicationsproducethedatatobetransferredoverthenetwork.Thislayer
alsoservesasawindowfortheapplicationservicestoaccessthenetworkand
fordisplayingthereceivedinformationtotheuser.
ProtocolsusedintheApplicationlayerareSMTP,FTP,DNS,etc.

11. Conclusion
Inconclusion,theOSI(OpenSystemsInterconnection)modelhelpsus
understandhowdatamovesinnetworks.Itconsistsofsevendistinctlayers:-
Physical,DataLink,Network,Transport,Session,Presentation,andApplication.
Eachlayerhasspecificresponsibilitiesandinteractswiththelayersdirectly
aboveandbelowit.Sinceitisaconceptualmodel,buttheOSIframeworkisstill
widelyusedtotroubleshootandunderstandnetworkingissues.

12. Thank You