Physical Layer.pdf

Lecture note

1. by
Dr. S. SELVAGANESAN
Professor and HoD / IT
[email protected]
CS8591 Computer Networks
1
UNIT I
Introduction and
Physical Layer

2. CS8591 COMPUTER NETWORKS -Syllabus
2

3. CS8591 COMPUTER NETWORKS -Books
3

4. UNIT I
Introduction and Physical
Layer
Networks–NetworkTypes–Protocol
Layering–TCP/IPProtocolsuite–
OSIModel–PhysicalLayer:
Performance–Transmissionmedia–
Switching – Circuit-switched
Networks–PacketSwitching.
4

5. Data Communication
DataCommunicationisthe
exchangeofdatabetweentwo
devicesviasomeformof
transmissionmedium(suchasawire
cable).
5

6. Data Communication
Characteristics:
Effectivenessofadatacommunicationsystemdependson:
Delivery:Thesystemmustdeliverdatatothecorrect
destination.
Accuracy:Thesystemmustdeliverthedataaccurately
(withoutanychange/alteration).
Timeliness:Thesystemmustdeliverthedatainatimely
manner.Inthecaseofvideoandaudio,timelydelivery
meansdeliveringthedataastheyareproduced,inthesame
order,thattheyareproduced,andwithoutsignificantdelay.
Thiskindofdeliveryiscalledreal-timetransmission.
Jitter:Jitterreferstothevariationinthepacketarrivaltime.
Itistheunevendelayinthedeliveryofaudioorvideo
packets
6

7. Components of Data communication
Components
ADataCommunicationsystemhasfivecomponents.
Figure 1: Five Components of Data Communication System
7

8. ADataCommunicationsystemconsistsoffivecomponents.Theyare
1.Sender:Thesenderisadevicethatsendsthemessage.Itcanbea
computer,workstation,telephonehandset,videocamera,andsoon.
2.Receiver:Thereceiverisadevicethatreceivesthemessagesentbythe
sender.Itcanbeacomputer,workstation,telephonehandset,television,and
soon.
3.Message:Themessageistheinformationordatatobecommunicated.
(Text,number,images,audioandvideo)
4.Medium:Thetransmissionmediumisthephysicalpathbywhicha
messagetravelsfromsendertoreceiver.Someexamplesoftransmission
mediaincludetwisted-pairwire,coaxialcable,fiber-opticcable,andradio
waves.
5.Protocol:Aprotocolisasetofrulesthatgoverndatacommunications.It
representsanagreementbetweenthecommunicatingdevices.Withouta
protocol,twodevicesmaybeconnectedbutnotcommunicating,justasa
personspeakingFrenchcannotbeunderstoodbyapersonwhospeaksonly
Japanese.
Components of Data communication
8

9. CommunicationbetweentwodevicescanbeSimplex,
Half-duplex,andfull-duplex.
Figure 2: Data flow (Simplex, Half-duplex, and full-duplex)
Data Flow (Transmission mode)
9

10. Communicationbetweentwodevicescanbeofthreetypes:
1.Simplex:Thecommunicationisunidirectional.Onlyoneof
thetwostationsonalinkcantransmitandothercanonly
receive.
Keyboardsandtraditionalmonitorsareexamplesof
simplexdevices.Thekeyboardcanonlyintroduceinput;
themonitorcanonlyacceptoutput.Thesimplexmode
canusetheentirecapacityofthechanneltosenddatain
onedirection.
2.Half-duplex:Eachstationcanbothtransmitandreceive;but
notatthesametime.Theentirecapacityofthechannelis
takenbythestationwhichtransmitsthedata.
Inahalf-duplextransmission,theentirecapacityofa
channelistakenoverbywhicheverofthetwodevicesis
transmittingatthetime.Walkie-talkiesandCB
(CitizensBand)radiosarebothhalf-duplexsystems.
Data Flow
10

11. Communicationbetweentwodevicescanbeofthree
types:
3.Full-duplex:Bothstationscantransmitandreceivethe
dataatthesametime.Thecapacityofthechannelis
dividedbetweenthesignalstravelingintheopposite
direction.
Onecommonexampleoffull-duplexcommunicationisthe
telephonenetwork.Whentwopeoplearecommunicatingbya
telephoneline,bothcantalkandlistenatthesametime.The
full-duplexmodeisusedwhencommunicationinboth
directionsisrequiredallthetime.Thecapacityofthechannel,
however,mustbedividedbetweenthetwodirections
Data Flow
11

12. NETWORKS
Anetworkisasetofdevices(alsoreferredtoas
nodes)connectedbycommunicationlinks.
Anodecanbeacomputer,printeroranyother
devicecapableofsendingand/orreceivingdata
generatedbyothernodesonthenetwork.
12

13. Computer NETWORKS
AComputernetworkisagroupof
interconnectedcomputers.
WhyweneedNetworks?
Itallowscomputerstocommunicatewith
eachotherandtoshareresourcesand
information.
Thebestknowncomputernetworkisthe
Internet.
13

14. NETWORKS
DistributedProcessing
Mostnetworksusedistributedprocessingin
whichataskisdividedamongmultiple
computers.
Insteadofonesinglelargemachinebeing
responsibleforallaspectsofaprocess,separate
computers(usuallyapersonalcomputeror
workstation)handleasubset.
14

15. NETWORKS
NetworkCriteria
Anetworkmustbeabletomeetacertain
numberofcriteria.Themostimportantof
thesecriteriaare
Performance
Reliability
Security
15

16. NETWORKS
Performance
Performancecanbemeasuredinmanyways,
includingtransittimeandresponsetime.
Transittimeistheamountoftimerequiredfora
messagetotravelfromonedevicetoanother.
Responsetimeistheelapsedtimebetweenan
inquiryandaresponse.
Performanceofanetworkdependsonanumber
offactorsincludingnumberofusers,typeof
transmissionmedium,capabilitiesofconnected
hardware,andefficiencyofsoftware.
16

17. NETWORKS
Performance
Performanceisoftenevaluatedbytwo
networkingmetrics:throughputanddelay.
Weoftenneedmorethroughputandlessdelay.
However,thesetwocriteriaareoften
contradictory.
Ifwetrytosendmoredatatothenetwork,
wemayincreasethroughputbutweincrease
thedelaybecauseoftrafficcongestioninthe
network.
17

18. NETWORKS
Reliability
Inadditiontoaccuracyofdelivery,network
reliabilityismeasuredbythefrequencyof
failure,thetimeittakesalinktorecoverfrom
afailure,andthenetwork’srobustnessina
catastrophe.
Security
Networksecurityissuesincludeprotecting
datafromunauthorizedaccess,protectingdata
fromdamageand,developmentand
implementingpoliciesandproceduresfor
recoveryfrombreachesanddatalosses.
18

19. Physical Structures
Type of Connection
Beforediscussingnetworks,weneedtodefinesome
networkattributes.
DirectionofDataFlow
Anetworkisasetoftwoormoredevicesconnected
throughlinks.
ALinkisthephysicalcommunicationpathwaythat
transfersdatafromonedevicetoanother.
LineConfigurationreferstothewaytwoormore
communicationdevicesattachtoalink.
Twotypesofconnections(LineConfiguration):
1.Point-to-Point
2.Multipoint
19

20. Point-to-PointLineConfigurationprovidesadedicatedlink
betweentwodevices.Theentirecapacityofthechannelis
reservedfortransmissionbetweenthosetwodevices.
Mostpoint-to-pointlineconfigurationuseanactuallengthof
wireorcabletoconnectthetwoends,butotheroptions,suchas
microwaveorsatellitelinksarealsopossible.
Example:1.Point-to-Pointconnectionbetweenremotecontrol
andTelevisionforchangingthechannels(throughinfraredray)
2.Acomputerconnectedbyatelephoneline.
Figure 3: Point-to-Point Line Configuration
Physical Structures
Type of Connection
20

21. MultipointLineConfigurationisoneinwhichmorethantwo
specificdevicesshareasinglelink.
Inamultipointenvironment,thecapacityofthechannelis
shared,eitherspatiallyortemporally.
Ifseveraldevicescanusethelinksimultaneously,itisaspatiallyshared
lineconfiguration.(Example:internetcommunication,Telephony
communication.)
Ifusersmusttaketurns,itisatime-sharedlineconfiguration.
(temporally)
Figure 4: Multipoint Line Configuration
Physical Structures
Type of Connection
21

22. Topology:Thetermtopologyreferstothewayanetworkis
laidoutphysically.
Twoormoredevicesconnecttoalink;twoormorelinks
formatopology.
Thetopologyofanetworkisthegeometricrepresentationof
therelationshipofallthelinksandlinkingdevices(usually
callednodes)toeachother.
Fourbasictopologies:
1.Mesh
2.Star
3.Bus
4.Ring
(Inaddition,Hybrid)
Physical Structures
Physical Topology
22

23. MeshTopology:
Everydevicehasadedicatedpoint-to-pointlinktoeveryotherdevice.
In a mesh (topology) network with nnodes, there are
direct links;
number of I/O ports (for each device) required is (n-1).
Advantages:
1.Meshtopologyisrobust
2.Betterprivacyandsecurity
3.Failureofonelinkwillnotdisturb
otherlinks
4.Helpsthenetworkmanagertofind
thefaultlocationandsolution
Disadvantages:
1.LargeamountofcablingandI/O
portsarerequired.
2.Installationandreconnectionare
difficult.
Physical Structures
Physical Topology
Fig.5: A fully connected mesh topology
(five devices)
23

24. Exercise
Inamesh(topology)networkwithnnodes,thereare direct
links.
No.ofportsoneachdevice=(n-1)
Problem:
Assumefivedevicesarearrangedinamesh
topology.Howmanycablesareneeded?How
manyportsareneededforeachdevice?
Ans:
No.ofcables= = =10
No.ofportsforeachdevice=(n-1)=5-1
=4
24

25. StarTopology:
Everydevicehasadedicatedpoint-to-pointlinktoacentral
controller(HUB)only.
InaStartopologynetworkwithnnodes,therearedirectnlinks;
Advantages:
1.Startopologyisrobust.
2.Lessexpensive.
3.Faultidentificationandfault
isolationareeasy.
4.Modificationofstarnetwork
iseasy.
Disadvantages:
1.Ifthecentralhubfails,the
wholenetworkwillnotwork.
2.Communicationispossible
throughthehub.
Physical Structures
Physical Topology
Fig.6: A star topology connecting five stations
25

26. Hub
Physical Structures
Physical Topology
Fig.7: A star topology connecting four stations
26

27. BusTopology:
Onelongcableactsasabackbonetolinkallthedevicesinthe
network
Nodesareconnectedtothebackbonebytapsanddroplines.
Droplineisestablishingtheconnectionbetweenthedevicesandthe
cable.Thetapsareusedasconnectors.
Advantages:
1.EasyInstallation.
2.Lesscablingandlessnumber
ofI/Oportsisrequired.
3.Lesscost.
Disadvantages:
1.Networktrafficishigh.
2.Faultisolationandreconnectionis
difficult.
3.Addingnewdeviceisdifficult.
4.Abreakinthebuscablestopsall
transmissions
Physical Structures
Physical Topology
Fig.8: A bus
topology
connecting
three stations
27

28. RingTopology:
Eachdevicehasadedicatedpoint-to-pointlinkwithonlythetwo
devicesoneithersideofit.
Asignalistravellingalongaringinonlyonedirectionfromdevice
todeviceuntilitreachesitsdestination.
Therepeaterisusedtoregeneratethesignalsduringtransmission.
Advantages:
1.Easytoinstallandreconfigure.
2.Linkfailurecanbeeasilyfound
out.
Disadvantages:
1.Maximumlengthofringand
numberofdevicesarelimited.
2.Failureofonenodeonthering
affectstheentirenetwork.
3.Additionofnodesorremovalof
nodesdisruptsthenetwork.
4.Signaltrafficisunidirectional.
Physical Structures
Physical Topology
Fig. 9: A ring topology connecting six stations
28

29. RingTopology:
InaRingtopologynetworkwithnnodes,
therearedirectnlinks;
Physical Structures
Physical Topology
Fig. 9: A ring topology connecting six stations
29

30. HybridTopology:
Ahybridtopologyisatypeofnetworktopologythatusestwoor
moreothernetworktopologies,includingbustopology,mesh
topology,ringtopology,startopology,andtreetopology.
Physical Structures
Physical Topology
Fig.10: A hybrid topology: a star backbone with three bus networks
30

31. HybridTopology:
Physical Structures
Physical Topology
Fig.11: A hybrid topology: a star backbone with three bus networks
31

32. Types of Networks
CategoriesofNetwork
32

33. LAN, MAN, and WAN
CategoriesofNetwork
33

34. Fig 12: LAN
Local Area Networks (LAN)
34

35. Figure 13 An isolated LAN connecting 12 computers to a hub in a closet
35

36. Fig 14: MAN 36

37. Fig.15: MAN
37

38. Fig.16: WAN
38

39. Categories of Networks
39

40. Local Area Networks (LAN)
40

41. Alocalareanetwork(LAN)isusually
privatelyownedandlinksthedevicesina
singleoffice,building,orcampus.
Dependingontheneedsofanorganizationand
thetypeoftechnologyused,aLANcanbeas
simpleastwoPCsandaprinterinsomeone's
homeoffice;oritcanextendthroughouta
companyandincludeaudioandvideo
peripherals.
Currently,LANsizeislimitedtoafew
kilometers(upto10kms.)
Local Area Networks (LAN)
41

42. LANsaredesignedtoallowresourcestobe
sharedbetweenpersonalcomputersor
workstations.Theresourcestobesharedcan
includehardware(e.g.,aprinter),software
(e.g.,anapplicationprogram),ordata.
AcommonexampleofaLAN,foundinmany
businessenvironments,linksaworkgroupof
task-relatedcomputers,forexample,
engineeringworkstationsoraccountingPCs.
Local Area Networks (LAN)
42

43. AMetropolitanAreaNetwork(MAN)isanetworkwitha
sizebetweenaLANandaWAN.
Itnormallycoverstheareainsideatownoracity.(10km
–100km)
Itisdesignedforcustomerswhoneedahigh-speed
connectivity,normallytotheInternet,andhaveendpoints
spreadoveracityorpartofcity.
AgoodexampleofaMANisthepartofthetelephone
companynetworkthatcanprovideahigh-speedDSLline
tothecustomer.
AnotherexampleisthecableTVnetworkthatoriginally
wasdesignedforcableTV,buttodaycanalsobeusedfor
high-speeddataconnectiontotheInternet.
Metropolitan Area Networks (MAN)
43

44. Awideareanetwork(WAN)provideslong-distancetransmissionof
data,image,audio,andvideoinformationoverlargegeographic
areasthatmaycompriseacountry,acontinent,oreventhewhole
world.
AWANcanbeascomplexasthebackbonesthatconnectthe
Internetorassimpleasadial-uplinethatconnectsahomecomputer
totheInternet.
WenormallyrefertothefirstasaswitchedWANandtothesecond
asapoint-to-pointWAN(Figure17).
TheswitchedWANconnectstheendsystems,whichusually
comprisearouter(internetworkingconnectingdevice)thatconnects
toanotherLANorWAN.
Thepoint-to-pointWANisnormallyalineleasedfromatelephone
orcableTVproviderthatconnectsahomecomputerorasmall
LANtoanInternetserviceprovider(lSP).ThistypeofWANis
oftenusedtoprovideInternetaccess.
Wide Area Networks (WAN)
44

45. Figure 17 WANs: a switched WAN and a point-to-point WAN
45

46. Interconnection of Networks:
Internet
Today,itisveryraretoseeaLAN,aMAN,oraLANinisolation;theyare
connectedtooneanother.Whentwoormorenetworksareconnected,they
becomeaninternetwork,orinternet.
Asanexample,assumethatanorganizationhastwooffices,oneontheeast
coastandtheotheronthewestcoast.Theestablishedofficeonthewest
coasthasabustopologyLAN;thenewlyopenedofficeontheeastcoasthas
astartopologyLAN.Thepresidentofthecompanylivessomewhereinthe
middleandneedstohavecontroloverthecompanyfromherhome.
TocreateabackboneWANforconnectingthesethreeentities(twoLANs
andthepresident'scomputer),aswitchedWAN(operatedbyaservice
providersuchasatelecomcompany)hasbeenleased.ToconnecttheLANs
tothisswitchedWAN,however,threepoint-to-pointWANsarerequired.
Thesepoint-to-pointWANscanbeahigh-speedDSLlineofferedbya
telephonecompanyoracablemodernlineofferedbyacableTVprovideras
showninFigure1.12. 46

47. Figure 18 A heterogeneous network made of four WANs and two LANs47

48. The Internet
Anetworkisagroupofconnecteddevicessuchas
computersandprinters.
Aninternetistwoormorenetworksthatcan
communicatewitheachother.
ThemostnotableinternetiscalledtheInternet.
TheInternetisacollaborationofmorethan
hundredsofinterconnectednetworks.
48

49. The Internet
In1969,aprojectwasfundedbytheAdvancedResearch
ProjectAgency,anarmoftheU.S.Departmentof
Defense.
ARPAestablishedapacket-switchingnetwork,called
AdvancedResearchProjectAgencyNetwork
(ARPANET).
In1972,VintCerfandBobKahn,collaboratedonwhat
theycalledtheInternettingProject.
49

50. Figure 19 Hierarchical organization of the Internet
50

51. Protocols and Standards
Protocolissynonymouswithrule.
Standardsareagreeduponrules.
51

52. Protocols and Standards
Protocols
Aprotocolisasetofrulesthatgovernsdata
communications.
Aprotocoldefineswhatiscommunicated,howitis
communicated,andwhenitiscommunicated.
Theimportantelementsofaprotocolare:Syntax,
Semanticsandtiming.
Syntax:Itreferstothestructureorformatofthedata(the
orderinwhichtheyarepresented).
Semantics:Itreferstothemeaningforeachsectionof
bits,howthedataisgoingtobeinterpretedandtheaction
tobetakenbasedontheinterpretation.
Timing:Itindicateswhenthedatashouldbesentandhow
fastthedatacanbesent.
52

53. Standards
Defacto:Thestandardsthathavenotbeenapproved
byanorganizationbodybuthavebeenadoptedas
standardsthroughwidespreadusearecalledDe
factoStandard.
Dejure:Standardsthathavebeenapprovedbyan
organizedbody.
StandardsOrganization
InternationalOrganizationforStandardization(ISO),
InternationalTelecommunicationUnion-Telecommunication
StandardsSector(ITU-T),
AmericanNationalStandardsInstitute(ANSI),
InstituteofElectricalandElectronicsEngineers(IEEE),
ElectronicIndustriesAssociation(EIA)
Protocols and Standards
53

54. Building a Network
AComputerNetworkmustprovideageneral,cost
effective,fairandrobustconnectivityamongalarge
numberofcomputers.
Networksmustevolvetoaccommodatechangesinboth
underlyingtechnologiesuponwhichtheyarebasedas
wellaschangesinthedemandsplacedonthemby
applicationprograms.
Todealwiththiscomplexity,networkdesignershave
developedgeneralblueprintcalledNetwork
Architecture.

55. Building a Network
ANetworkArchitectureisdefinedaswhichidentifies
theavailablehardwareandsoftwarecomponentsand
showshowtheycanbearrangedtoformacomplete
network.
Tobuildanetwork,wemustknowthefollowing
things.
Discovertherequirementsthatdifferentapplicationsand
differentcommunitiesofpeopleplaceonthenetwork.
NetworkArchitectureonwhichtheapplicationsaregoingto
bedeveloped.
Keyelementsintheimplementationofcomputernetworks.
Identifyingkeymetricsthatareusedtoevaluatethe
performanceofcomputernetworks.

56. Building a Network
Networkingisaplanned,andongoingeffort.
Wesetgoals,developstrategiesforachievingthem,
takeaction,evaluatehowwellourplanisworking,and
makechangesasnecessary.
Howtobuildanetworkinfivesteps:
1.MakeaNetworkingPlan
2.Makecontact
3.Organizeournetwork
4.Takeaction;and
5.Practicenetworkingetiquette

57. Building a Network
Applications
Someapplicationsofthecomputernetworksare:
WorldWideWeb(WWW)
Email
Streamingaudioandvideo
Chatrooms
Music(file)sharing

58. Requirements
Requirements
Forbuildingacomputernetwork,wemustidentify
thesetofconstraintsandrequirementsthatinfluence
networkdesignandtheexpectationswehavefora
networkdependonourperspective:
AnApplicationProgrammerwouldlisttheservicesthat
theapplicationneeds.
ANetworkDesignerwouldlistthepropertiesofacost-
effectivedesign.
ANetworkProviderwouldlistthecharacteristicsofa
systemthatiseasytoadministerandmanage.

59. Layered Tasks
Weusetheconceptoflayersinourdailylife.
Asanexample,letusconsidertwofriendswho
communicatethroughpostalmail.
Theprocessofsendingalettertoafriendwould
becomplexiftherewerenoservicesavailablefrom
thepostoffice.
Figureshowsthestepsinthistask.

60. Figure -Tasks involved in sending a letter
Layered Tasks

61. Sender,Receiver,andCarrier
InFigure,wehaveasender,areceiver,andacarrierthattransportstheletter.Thereisa
hierarchyoftasks.
AttheSenderSite
Letusfirstdescribe,inorder,theactivitiesthattakeplaceatthesendersite.
oHigherlayer.Thesenderwritestheletter,insertstheletterinanenvelope,writes
thesenderandreceiveraddresses,anddropstheletterinamailbox.
oMiddlelayer.Theletterispickedupbyalettercarrieranddeliveredtothepost
office.
oLowerlayer.Theletterissortedatthepostoffice;acarriertransportstheletter.
OntheWay
Theletteristhenonitswaytotherecipient.Onthewaytotherecipient'slocalpost
office,thelettermayactuallygothroughacentraloffice.Inaddition,itmaybetrans
portedbytruck,train,airplane,boat,oracombinationofthese.
AttheReceiverSite
oLowerlayer.Thecarriertransportsthelettertothepostoffice.
oMiddlelayer.Theletterissortedanddeliveredtotherecipient'smailbox.
oHigherlayer.Thereceiverpicksuptheletter,openstheenvelope,andreadsit.
Layered Tasks

62. Layering and Protocols
Layeringisthetechniquefororganizingtheprotocolsintoan
orderedseriesofdistinctabstractions.
Theservicesprovidedbyalayerdependonlyontheservices
providedbythepreviouslessabstractlayer.
Thelayerimmediatelyabovethehardwaremightprovidehost-
to-hostconnectivity.
Thenextlayerupprovidesthesupportforprocess-to-process
channels.
Figure: Example of a layered network system

63. Layering and Protocols
Layeringprovidestwonicefeatures:
1.Itdecomposestheproblemofbuildinganetworkintomoremanageable
components.
2.Itprovidesamoremodulardesign.
Ifwewanttoaddanewservice,wehavetomodifythefunctionalityat
onelayer,reusingthefunctionsprovidedatallotherlayers.
Intheabovefigure,onechannelprovidesarequest/replyservice,and
anotherchannelprovidesamessagestreamservice.
Theabstractobjectsthatmakeupthelayersofanetworksystemare
calledprotocols.Thatis,aprotocolprovidesacommunicationservice
thathigher-levelobjectsusetoexchangemessages.
Figure: Layered systems with alternative abstractions

64. OSI Model
OpenSystemsInterconnection(OSI)Model
AnISOstandardthatcoversallaspectsofnetwork
communicationsistheOpenSystemsInterconnection(OSI)
model.
Itwasfirstintroducedinthelate1970s.
Anopensystemisamodelthatallowsanydifferentsystemsto
communicateregardlesstotheirunderlyingarchitecture.
ThepurposeofOSImodelistoopencommunicationsbetween
differentsystemswithoutrequiringchangestothelogicofthe
underlyinghardwareandsoftware.
TheOSImodelisnotaprotocol;itisamodelforunderstanding
anddesigninganetworkarchitecturethatisflexible,robust,and
interoperable.

65. OSI Model
OpenSystemsInterconnection(OSI)
TheOpenSystemsInterconnectionmodelisalayeredframeworkforthe
designofnetworksystemsthatallowsforcommunicationacrossalltypesof
computersystems.
Itconsistsforsevenseparatebutrelatedlayers,eachofwhichdefinesa
segmentoftheprocessofmovinginformationacrossanetwork.

66. OSI Model

67. OSI Model
ThefiguregivesanoverallviewoftheOSIlayers.
Figure –The Interaction between layers in the OSI model

68. Layered Architecture (OSI Model)
OpenSystemsInterconnection(OSI).
Figureshowsthelayersinvolvedwhenamessageissentfrom
deviceAtodeviceB.
AsthemessagetravelsfromAtoB,itmaypassthroughmany
intermediatenodes.
Theseintermediatenodesusuallyinvolveonlythefirstthree
layersoftheOSImodel
Eachlayercallsupontheservicesofthelayersjustbelowit.
Thisisdonewiththehelpofprotocols.
Theprocessesoneachmachinethatcommunicateatagiven
layerarecalledPeer-to-PeerProcesses.
Thepassingofdataandnetworkinformationbetweenthelayers
arecarriedoutwiththehelpofinterfaces.Interfaceisusedto
definetheinformationandservicestobeprovidedbyeachlayer.

69. Peer-to-Peer Process
Atthephysicallayer,communicationisdirect.
InFigure,deviceAsendsastreamofbitstodeviceB
(throughintermediatenodes).
Atthehigherlayers,however,communicationmustmove
downthroughthelayersondeviceA,overtodeviceB,and
thenbackupthroughthelayers.
Eachlayerinthesendingdeviceaddsitsowninformationto
themessageitreceivesfromthelayerjustaboveitandpasses
thewholepackagetothelayerjustbelowit.
Atlayer1,theentirepackageisconvertedtoaformthatcan
betransmittedtothereceivingdevice.
Atthereceivingmachine,themessageisunwrappedlayerby
layer,witheachprocessreceivingandremovingthedata
meantforit.

70. Thepassingofthedataandnetworkinformationdown
throughthelayersofthesendingdeviceandbackup
throughthelayersofthereceivingdeviceismadepossible
byaninterfacebetweeneachpairofadjacentlayers.
Eachinterfacedefinestheinformationandservicesalayer
mustprovideforthelayeraboveit.
Well-definedinterfacesandlayerfunctionsprovide
modularitytoanetwork.
Aslongasalayerprovidestheexpectedservicestothe
layeraboveit,thespecificimplementationofitsfunctions
canbemodifiedorreplacedwithoutrequiringchangesto
thesurroundinglayers.
Interfaces Between Layers

71. OSI Model
Thefiguregivesanoverallviewofthe
OSIlayers.
Figure –The Interaction between layers in the OSI
model
Thesevenlayersare
organizedintothree
subgroups.
#Layers1,2and3
(Physical,DataLinkand
Networklayers)are
NetworkSupportLayers.
#Layers5,6and7
(Session,Presentationand
Applicationlayers)are
UserSupportLayers.
#Layer4(TransportLayer)
linksthetwosubgroups
andensuresthatwhat
lower layershave
transmittedisinaformthat
theupperlayerscanuse.

72. OSI Model
NetworksupportLayerdealwiththephysicalaspectsofmoving
datafromonedevicetoanothersuchaselectricalspecifications,
physicalconnections,physicaladdressingandtransporttimingand
reliability.
UsersupportLayersallowinteroperabilityamongunrelated
softwaresystems.
TheupperOSIlayersarealwaysimplementedinsoftware.Lower
layersareacombinationofhardwareandsoftware,exceptforthe
physicallayer,whichismostlyhardware.

73. OSI Model
Figure –An Exchange using the OSI model

74. OSI Model
•Theprocessstartsattheapplicationlayer;
thenmovesfromlayertolayerin
descendingsequentialorder.
•Ateachlayer,aheader,canbeaddedtothe
dataunit.
•Thetrailerisaddedonlyatlayer2.
•Whentheformatteddataunitpasses
throughthephysicallayer,itischangedinto
anelectromagneticsignalandtransported
alongthephysicallink.
•Uponreachingitsdestination,thesignal
passesintophysicallayerandistransformed
backintodigitalform.
•Thedataunitsarethenmovedbackup
throughtheOSIlayers.
•Whentheblockofdatareachesthenext
higherlayer,theheadersandtrailersattached
bythesendinglayerareremoved.
•Whenthedataunitreachestheapplication
layer,themessageisagaininform
appropriatetotheapplicationandismade
availabletotherecipient.
Figure –An Exchange using the OSI model

75. Encapsulation
Figure2.3revealsanotheraspectofdatacommunicationsin
theOSImodel:encapsulation.
Apacket(headeranddata)atlevel7isencapsulatedina
packetatlevelwholepacketatlevel6isencapsulatedina
packetatlevel5,andsoon.
Inotherwords,thedataportionofapacketatlevelN-1
carriesthewhole(dataandheaderandmaybetrailer)from
levelN.Theconceptiscalledencapsulation;levelN-1isnot
awareofwhichpartoftheencapsulatedpacketisdataand
whichistheheaderortrailer.
ForlevelN-1,thewholepacketcomingfromlevelNasone
integralunit.

76. Layers in the OSI Model

77. Physical Layer
PhysicalLayer
Thephysicallayerisresponsibleformovementsofindividualbits
fromonehop(node)tothenext.
Thephysicallayercoordinatesthefunctionsrequiredtocarryabit
streamoveraphysicalmedium.
Itdealswiththemechanicalandelectricalspecificationsofthe
interfaceandthetransmissionmedium.

78. FunctionsofPhysicalLayer
1.PhysicalCharacteristicsofInterfacesandMedia:
•Itdefinestheelectricalandmechanicalcharacteristicsoftheinterfaceandthemedia.
•Itdefinesthetypesoftransmissionmedium.
2.RepresentationofBits
•Totransmitthestreamsofbitstheymustbeencodedintosignal.
•Itdefinesthetypeofencodingwhetherelectricaloroptical.
3.Datarate
•Itdefinesthetransmissionrate,i.e.,thenumberofbitssentpersecond.
4.SynchronizationofBits
•Thesenderandreceivermustbesynchronizedatbitlevel.
5.LineConfiguration
•Itdefinesthetypeofconnectionbetweenthedevices
•Twotypesofconnectionare:Point-to-Point;Multipoint
6.PhysicalTopology
•Thesenderandreceivermustbesynchronizedatbitlevel.
7.TransmissionMode
•Thephysicallayeralsodefinesthedirectionoftransmissionbetweentwodevices:
Simplex,Half-duplex,Full-duplex.
Physical Layer

79. 2.79
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note

80. DataLinkLayer
Thedatalinklayerisresponsibleformovingframesfromonehop
(node)tothenext.
Data Link Layer

81. FunctionsofDataLinkLayer
1.Framing:Itdividesthestreamofbitsreceivedfromnetworklayerinto
manageabledataunitscalledframes.
2.PhysicalAddressing:Itaddsaheadertotheframetodefinethesender
andreceiveroftheframe.
3.FlowControl:Thedatalinklayerimposesaflowcontrolmechanismto
avoidoverwhelmingthereceiver.
4.ErrorControl
•Itaddsreliabilitybyaddingmechanismstodetectandretransmit
damagedorlostframes.
•Italsousesamechanismtorecognizeduplicateframesbyaddingthe
trailertotheendoftheframe
5.AccessControl
•Itdetermineswhichdevicehascontroloverthelinkatanygiven
timewhentwoormoredevicesareconnectedtothesamelink.
Data Link Layer

82. Sub-layersofDataLinkLayer
1.LogicalLinkControl(LLC)Layer
•TheLogicalLinkControl(LLC)layerisoneoftwosub-layers
thatmakeuptheDataLinkLayeroftheOSImodel.
•TheLogicalLinkControllayercontrolsframe
synchronization,flowcontrolanderrorchecking.
2.MediaAccessControl(MAC)Layer
•TheMediaAccessControlLayerisoneoftwosub-layersthat
makeuptheDataLinkLayeroftheOSImodel.
•TheMAClayerisresponsibleformovingdatapacketstoand
fromoneNetworkInterfaceCard(NIC)toanotheracrossa
sharedchannel.
Data Link Layer

83. The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

84. 2.84
Figure 2.7 Hop-to-hop delivery

85. Physical Addressing

86. Network Adapter

87. NetworkLayer
Thenetworklayerisresponsibleforthedeliveryofindividualpackets
fromsourcehosttothedestinationhost.
Network Layer

88. OtherresponsibilitiesofNetworkLayer
1.LogicalAddressing:Whenapacketpassesthenetwork
boundary,thenetworklayeraddsthelogicaladdressesof
thesenderandreceiver.
2.Routing:Whenindependentnetworksorlinksare
connectedtocreateinternetworks,theconnectingdevices
(calledroutersorswitches)routeorswitchthepacketsto
theirfinaldestination.
Network Layer

89. 2.89
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note

90. 2.90
Figure 2.9 Source-to-destination delivery

92. TransportLayer
Thetransportlayerisresponsibleforthedeliveryofamessagefrom
oneprocesstoanother.
Transport Layer

93. Transport Layer
OtherresponsibilitiesofTransportLayer
1.Service-pointaddressing:Thetransportlayergetstheentire
messagetothecorrectprocessonthedestinationsystemsbyaddinga
typeofaddresscalledaservice-pointaddress(orportaddress).
2.Segmentationandreassembly:Amessageisdividedinto
transmittablesegments,witheachsegmentcontainingasequence
number.Thesenumbersareusedtoreassemblethemessageatthe
destinationandtoidentifyandreplacepacketsthatwerelostin
transmission.
3.ConnectionControl:Inaconnectionlessservice,eachsegmentis
treatedasindependentpacketandinconnectionorientedservice,
eachsegmentistreatedasdependentpacket.Afterallthedataare
transferred,theconnectionisterminated.
4.FlowControl:Flowcontrolisperformedfromendtoendratherthan
acrossasinglelink.
5.ErrorControl:Atthislayer,theerrorcontrolisperformedina
process-to-processratherthanacrossasinglelink.

94. 2.94
The transport layer is responsible for the delivery
of a message from one process to another.
Note

95. 2.95
Figure 2.11 Reliable process-to-process delivery of a message

96. Port Address

97. Port Address

98. Session Layer
SessionLayer

99. Session Layer
SpecificresponsibilitiesofSessionLayer
1.DialogControl:Thesessionlayerallowstwosystemsto
enterintoadialog.Itallowsthecommunicationbetween
twoprocessestotakeplaceineitherhalf-duplexorfull-
duplexmode.
2.Synchronization:Thesessionlayerallowsaprocesstoadd
checkpoints,orsynchronizationpoints,toastreamofdata.
•E.g.Ifasystemissendingafileof100pages,itisadvisableto
insertcheckpointsafterevery10pagestoensurethateach10-
pageunitisreceivedandacknowledgedindependently.Inthis
case,ifacrashhappensduringthetransmissionofpage23,the
onlypagesthatneedtoberesentaftersystemrecoveryare
pages21to30.

100. 2.100
The session layer is responsible for dialog
control and synchronization.
Note

101. Presentation Layer
PresentationLayer
Thepresentationlayerisresponsiblefortranslation,compression,and
encryption.

102. Presentation Layer
SpecificresponsibilitiesofPresentationLayer
1.Translation:Presentationlayerisresponsibleforthe
interoperabilitybetweendifferentencodingmethods.
2.Encryption:Tocarrysensitiveinformation,asystemmust
beabletoensureprivacy.Encryptionmeansthatthesender
transformstheoriginalinformationtoanotherformandsend
theresultingmessageoutoverthenetwork.Decryption
reversestheoriginalprocesstotransformthemessageback
toitsoriginalform.
3.Compression:Datacompressionreducesthenumberofbits
containedintheinformation.Datacompressionisimportant
inthetransmissionofmultimediasuchastext,audioand
video.

103. 2.103
The presentation layer is responsible for translation,
compression, and encryption.
Note

104. Application Layer
ApplicationLayer:isresponsibleforprovidingservicestothe
user.

105. Application Layer
SpecificservicesprovidedbyApplicationLayer:
1.NetworkVirtualTerminal:isasoftwareversionofa
physicalterminalanditallowsausertologontoaremote
host.
2.Filetransfer,access,andmanagement:Theapplication
allowsausertoaccessfilesinaremotehost,toretrievefiles
fromaremotecomputerforuseinthelocalcomputer,andto
manageorcontrolfilesinaremotecomputerlocally.
3.MailServices:Thisapplicationprovidesthebasisfore-mail
forwardingandstorage.
4.DirectoryServices:Thisapplicationprovidesdistributed
sourcesandaccessforglobalinformationaboutvarious
objectsandservices.

106. 2.106
The application layer is responsible for
providing services to the user.
Note

107. OSI Models
Summary of Layers

111. Data Link Layer also adds a trailer
-Trailer contains additional information that
deals with error correction.

113. Internet Architecture
Internetarchitectureisameta-network,aconstantly
changingcollectionofthousandsofindividualnetworks
intercommunicatingwithacommonprotocol.
Internetarchitectureisdescribedinitsname,theshortform
of‘inter-networking’.
Thisarchitectureisbasedontheveryspecificationofthe
standardTCP/IPprotocol,designedtoconnectanytwo
networkswhichmaybeverydifferentininternalhardware,
softwareandtechnicaldesign.
Oncetwonetworksareinterconnected,communicationwith
TCP/IPisenabledend-to-end,sothatanynodeonthe
Internethastheabilitytocommunicatewithanyothernode
(onanywhere).TheInternetarchitectureisalsosometimes
calledtheTCP/IParchitecture.

114. TCP/IP Protocol Suite
TheTCP/IPprotocolsuitewasdevelopedpriortotheOSI
model.Therefore,thelayersintheTCP/IPprotocolsuitedo
notexactlymatchthoseintheOSImodel.
TheoriginalTCP/IPprotocolsuitewasdefinedashaving
fourlayers:host-to-network,internet,transport,and
application.
TheTCP/IPprotocolsuiteismadeoffivelayers:Physical,
Datalink,Network,Transport,andApplication.
Thefirstfourlayersprovidephysicalstandards,network
interfaces,internetworking,andtransportfunctionsthat
correspondtothefirstfourlayersoftheOSImodel.
ThethreetopmostlayersintheOSImodel,however,are
representedinTCP/IPbyasinglelayercalledthe
applicationlayer(seeFigure).

115. 2.115
Figure 2.16 TCP/IP and OSI model

116. TCP/IP Protocol Suite
1.PhysicalandDataLinkLayers:
Atthephysicalanddatalinklayers,TCP/IPdoes
notdefineanyspecificprotocol.
Itsupportsallthestandardandproprietary
protocols.
AnetworkinaTCP/IPinternetworkcanbea
local-areanetworkorawide-areanetwork.

117. TCP/IP Protocol Suite
2.NetworkLayer:
Atthenetworklayer(or,moreaccurately,theinternetworklayer),
TCP/IPsupportstheInternetworkingProtocol.IP,inturn,usesfour
Supportingprotocols:ARP,RARP,ICMP,andIGMP.
a.InternetworkingProtocol(IP)
TheInternetworkingProtocol(IP)isthetransmission
mechanismusedbytheTCP/IPprotocols.TheIPlayerprovides
anunreliable,connectionlessdeliverysystem.Thereasonwhyit
isunreliableisthatIPprovidesnoerrorcheckingortracking.
b.AddressResolutionProtocol
TheAddressResolutionProtocol(ARP)isusedtoassociatea
logicaladdresswithaphysicaladdress.Onatypicalphysical
network,suchasaLAN,eachdeviceonalinkisidentifiedbya
physicalorstationaddress,usuallyimprintedonthenetwork
interfacecard(NIC).ARPisusedtofindthephysicaladdressofthe
nodewhenitsInternetaddressisknown.

118. TCP/IP Protocol Suite
2.NetworkLayer:(Contd)
c.ReverseAddressResolutionProtocol
TheReverseAddressResolutionProtocol(RARP)allowsa
hosttodiscoveritsInternetaddresswhenitknowsonlyits
physicaladdress.Itisusedwhenacomputerisconnectedtoa
networkforthefirsttimeorwhenadisklesscomputeris
booted.
d.InternetControlMessageProtocol
TheInternetControlMessageProtocol(ICMP)isamechanism
usedbyhostsandgatewaystosendnotificationofdatagram
problemsbacktothesender.ICMPsendsqueryanderror
reportingmessages.
e.InternetGroupMessageProtocol
TheInternetGroupMessageProtocol(IGMP)isusedto
facilitatethesimultaneoustransmissionofamessagetoa
groupofrecipients.

119. TCP/IP Protocol Suite
3.TransportLayer:
TraditionallythetransportlayerwasrepresentedinTCP/IPby
twoprotocols:TCPandUDP.
IPisahost-to-hostprotocol,meaningthatitcandeliverapacket
fromonephysicaldevicetoanother.
UDPandTCParetransportlevelprotocolsresponsiblefor
deliveryofamessagefromaprocess(runningprogram)to
anotherprocess.Anewtransportlayerprotocol,SCTP,hasbeen
devisedtomeettheneedsofsomenewerapplications.
a.UserDatagramProtocol
TheUserDatagramProtocol(UDP)isthesimplerofthetwo
standardTCP/IPtransportprotocols.
Itisaprocess-to-processprotocolthataddsonlyport
addresses,checksumerrorcontrol,andlengthinformationto
thedatafromtheupperlayer.

120. TCP/IP Protocol Suite
4.TransportLayer:(Contd)
b.TransmissionControlProtocol(TCP)
TheTransmissionControlProtocol(TCP)providesfulltransport-
layerservicestoapplications.
TCPisareliablestreamtransportprotocol.Thetermstream,in
thiscontext,meansconnection-oriented:Aconnectionmustbe
establishedbetweenbothendsofatransmissionbeforeeithercan
transmitdata.
Atthesendingendofeachtransmission,TCPdividesastreamof
dataintosmallerunitscalledsegments.Eachsegmentincludesa
sequencenumberforreorderingafterreceipt,togetherwithan
acknowledgmentnumberforthesegmentsreceived.Segments
arecarriedacrosstheinternetinsideofIPdatagrams.Atthe
receivingend,TCPcollectseachdatagramasitcomesinand
reordersthetransmissionbasedonsequencenumbers.

121. TCP/IP Protocol Suite
4.TransportLayer:(Contd)
c.StreamControlTransmissionProtocol(SCTP)
TheTransmissionControlProtocol(TCP)provides
fulltransport-layerservicestoapplications.Anew
transportlayerprotocol,SCTP,hasbeendevisedto
meettheneedsofsomenewerapplications.
TheStreamControlTransmissionProtocol(SCTP)
providessupportfornewerapplicationssuchasvoice
overtheInternet.Theapplicationsthatderivethe
mostbenefitfromtheuseofSCTPareinthevoice
andvideocommunicationsarea.
Itisatransportlayerprotocolthatcombinesthebest
featuresofUDPandTCP.

122. TCP/IP Protocol Suite
5.ApplicationLayer:
TheapplicationlayerinTCP/IPisequivalentto
thecombinedsession,presentationand
applicationlayersintheOSImodel.Many
protocolsaredefinedatthislayer.

123. ADDRESSING
Fourlevelsofaddressesareusedinaninternet
employingtheTCP/IPprotocols:physical,logical,port,
andspecific.
Figure:Addresses in TCP/IP

124. 2.124
Figure: Relationshipof layers and addresses in TCP/IP

125. Physical Addressing

126. Network Adapter

128. Port Address

129. Port Address

130. TheInternet Assigned Numbers Authority(IANA) is responsible for the global
coordination of the DNS Root, IP addressing, and other Internet protocol resources.
The port numbers are divided into three ranges: thewell-known ports, theregistered
ports, and thedynamicorprivate ports.
The well-known ports (also known assystem ports) are those from 0 through 1023.
The requirements for new assignments in this range are stricter than for other
registrations,
[2]
examples include:
21:File Transfer Protocol(FTP)
22:Secure Shell(SSH)
23:Telnetremote login service
25:Simple Mail Transfer Protocol(SMTP)
53:Domain Name System(DNS) service
80:Hypertext Transfer Protocol(HTTP) used in theWorld Wide Web
110:Post Office Protocol(POP3)
119:Network News Transfer Protocol(NNTP)
123:Network Time Protocol(NTP)
143:Internet Message Access Protocol(IMAP)
161:Simple Network Management Protocol(SNMP)
194:Internet Relay Chat(IRC)
443:HTTP Secure(HTTPS)
The registered ports are those from 1024 through 49151. IANA maintains the official
list of well-known and registered ranges.The dynamic or private ports are those from
49152 through 65535. One common use for this range is forephemeral ports.

131. Specific Address

132. Performance
NetworkPerformanceMonitoring
Thegoalofnetworkperformancemonitoringtoolsistoprovidea
depictionofoperations,sopotentialproblemscanbeavoided,and
anomaliesthatoccurcanbedetected,isolatedandresolvedwitha
minimummean-time-to-repair.
BandwidthandLatency
Networkperformanceismeasuredintwofundamentalways:
Bandwidth
Latency(alsocalleddelay)
TheBandwidthofanetworkisgivenbythenumberofbitsthat
canbetransmittedoverthenetworkinacertainperiodoftime.
TheLatencyofanetworkisgivenbytime,takenbyamessage
totravelfromoneendofanetworktoother.

133. Performance
Throughputisameasureofhowfastwe
canactuallysenddatathroughanetwork.
Althoughbandwidthinbitspersecondand
throughputseemthesame,theyare
different.

134. Anetworkwithbandwidthof10Mbpscanpassonlyanaverageof12,000framesper
minutewitheachframecarryinganaverageof10,000bits.Whatisthethroughputof
thisnetwork?
Solution
Wecancalculatethethroughputas
Example 3.44
Thethroughputisalmostone-fifthofthebandwidthinthiscase.

135. Performance
TheLatencyordelaydefineshowlongittakesforanentiremessage
tocompletelyarriveatthedestinationfromthetimethefirstbitissent
outfromthesource.
Latencyismadeoffourcomponents:Propagationtime,
Transmissiontime,QueuingtimeandProcessingdelay.
Wecandefinethetotallatencyas
Latency=Propagation time + Transmission time + Queuing time + Processing delay
PropagationTime:measuresthetimerequiredforabittotravel
fromthesourcetothedestination.
Propagationtime=Distance/PropagationSpeed
Thepropagationspeedofelectromagneticsignalsdependsonthe
mediumandonthefrequencyofthesignal.
Lighttravelsat3×10
8
m/sinavacuum;2.3×10
8
m/sina
cable;2×10
8
m/sinafiber.

136. Whatisthepropagationtimeifthedistancebetweenthetwopointsis12,000km?
Assumethepropagationspeedtobe2.4×10
8
m/sincable.
Solution
Wecancalculatethepropagationtimeas
Example 3.45
TheexampleshowsthatabitcangoovertheAtlanticOceaninonly50msifthere
isadirectcablebetweenthesourceandthedestination.

137. Performance
TransmissionTime:
Transmission time= Message size / Bandwidth

138. Whatarethepropagationtimeandthetransmissiontimefora2.5-kbytemessage(an
e-mail)ifthebandwidthofthenetworkis1Gbps?Assumethatthedistancebetween
thesenderandthereceiveris12,000kmandthatlighttravelsat2.4×10
8
m/s.
Solution
Wecancalculatethepropagationandtransmissiontimeasshownonthenextslide:
Example 3.46
Propagation time = Distance / Propagation Speed
Transmission time = Message size / Bandwidth

139. Whatarethepropagationtimeandthetransmissiontimefora5-Mbytemessage
(animage)ifthebandwidthofthenetworkis1Mbps?Assumethatthedistance
betweenthesenderandthereceiveris12,000kmandthatlighttravelsat2.4×
10
8
m/s.
Solution
Wecancalculatethepropagationandtransmissiontimesasshownonthenext
slide.
Example 3.47

140. Notethatinthiscase,becausethemessageisverylongandthebandwidthisnot
veryhigh,thedominantfactoristhetransmissiontime,notthepropagationtime.
Thepropagationtimecanbeignored.
Example 3.47 (continued)

141. Queuing Time:

142. 3.142
The bandwidth-delay product defines the
number of bits that can fill the link.
Note

143. 3.143
Figure 3.33 Concept of bandwidth-delay product

144. Performance
Delay×BandwidthProduct
Itisusefultotalkabouttheproductofthesetwometrics,often
calledthedelay×bandwidthproduct.
Now,wewillthinkaboutachannelbetweenapairofprocesses
asahollowpipe,wherethelatencycorrespondstothelengthof
thepipeandthebandwidthgivesthediameterofthepipe,then
thedelay×bandwidthproductgivesthevolumeofthepipe–
themaximumnumberofbitsthatcouldbeintransmitthrough
thepipeatanygiveninstant.

145. Performance
Delay×BandwidthProduct
Forexample,atranscontinentalchannelwithone-waylatencyof
50msandabandwidthof45Mbpsisabletohold
=50×10
-3
sec×45×10
6
bits/sec
=2.25×10
6
bits
=275KBofdata

146. Figure Transmission medium and physical layer
•Transmission media are actually located below the physical layer
and are directly controlled by the physical layer.
•Figure shows the position of transmission media in relation to the
physical layer.
Transmission Media

147. Figure : Classes of transmission media
•Atransmissionmediumcanbebroadlydefinedasanything
thatcancarryinformationfromasourcetoadestination.
•Intelecommunications,transmissionmediacanbedividedinto
twobroadcategories:guidedandunguided.
•Guidedmediaincludetwisted-paircable,coaxialcable,and
fiber-opticcable.Unguidedmediumisfreespace.
Classes of Transmission Media

148. GUIDED MEDIA
Guidedmedia,whicharethosethatprovideaconduit
fromonedevicetoanother,includetwisted-paircable,
coaxialcable,andfiber-opticcable.
1.Twisted-Pair Cable
2.Coaxial Cable
3.Fiber-Optic Cable

149. Figure: Twisted-pair cable
1.Twisted-PairCable
Atwistedpairconsistsoftwoconductors(normally
copper),eachwithitsownplasticinsulation,twisted
together.
Oneofthewiresisusedtocarrysignalstothe
receiver,andtheotherisusedonlyasaground
reference.
Twisted-Pair Cable

150. Figure: UTP and STP cables
Unshielded Versus Shielded Twisted-Pair Cable
The most common twisted-pair cable used in communications is referred to as
unshielded twisted-pair (UTP).
IBM has also produced a version of twisted-pair cable for its use called shielded
twisted-pair (STP). STP cable has a metal foil or braided mesh covering that
encases each pair of insulated conductors. Although metal casing improves the
quality of cable by preventing the penetration of noise or crosstalk, it is bulkier
and more expensive.
Figure shows the difference between UTP and STP.
Twisted-Pair Cable

151. 7.151
Table : Categories of unshielded twisted-pair cables

152. Figure UTP connector
Connectors
ThemostcommonUTPconnectorisRJ45(RJstandsforregisteredjack),asshownin
Figure.TheRJ45isakeyedconnector,meaningtheconnectorcanbeinsertedinonlyone
way.
Twisted-Pair Cable

153. Applications
1.Twisted-paircablesareusedintelephonelines.
2.TPusedintelephonenetwork.
3.InLAN,TPwiresaremainlyusedforlowcost,low
performanceapplications.
Twisted-Pair Cable

154. Figure: UTP performance

155. Figure Coaxial cable
Coaxial Cable
Coaxial cable (or coax) carries signals of higher frequency ranges than
those in twisted pair cable.
It has a central core conductor of solid or stranded wire (usually copper)
enclosed in an insulating sheath, which is, in turn, encased in an outer
conductor of metal foil, braid, or a combination of the two.
The outer conductor is also enclosed in an insulating sheath, and the
whole cable is protected by a plastic cover (see Figure)

156. Table: Categories of coaxial cables
Coaxial Cable

157. Figure BNC connectors
Coaxial Cable

158. Figure: Coaxial cable performance

159. Coaxial Cable

160. Fiber-optic Cable

161. Fiber-optic Cable

162. Fiber-optic Cable

163. Propagation modes
Figure: Modes
1.Single-mode fiber
Carries light pulses along single path.
2.Multimode fiber
Many pulses of light travel at different angles
Fiber-optic Cable

164. Inmultimodestep-indexfiber,thedensityofthecoreremainsconstantfrom
thecentertotheedges.Abeamoflightmovesthroughthisconstantdensity
inastraightlineuntilitreachestheinterfaceofthecoreandthecladding.At
theinterface,thereisanabruptchangeduetoalowerdensity;thisaltersthe
angleofthebeam'smotion.Thetermstepindexreferstothesuddennessof
thischange,whichcontributestothedistortionofthesignalasitpasses
throughthefiber.
Inmultimodegraded-indexfiber,decreasesthisdistortionofthesignal
throughthecable.Thewordindexherereferstotheindexofrefraction.As
wesawabove,theindexofrefractionisrelatedtodensity.Agraded-index
fiber,therefore,isonewithvaryingdensities.Densityishighestatthecenter
ofthecoreanddecreasesgraduallytoitslowestattheedge.Figure7.13
showstheimpactofthisvariabledensityonthepropagationoflightbeams.
Fiber-optic Cable

165. Applications: Fiber-optic cable is often found in backbone networks because its
wide bandwidth is cost-effective. Today, with wavelength-division multiplexing
(WDM), we can transfer data at a rate of 1600 Gbps.
Advantages Fiber-optic cable has several advantages over metallic cable
(twisted-pair or coaxial).
1. Higher bandwidth. 2. Less signal attenuation. 3. Immunity to
electromagnetic interference.
4.Resistance to corrosive materials. 5. Light weight. 6. Greater immunity
to tapping.
Disadvantages There are some disadvantages in the use of optical fiber.
1. Installation and maintenance. Fiber-optic cable is a relatively new technology.
Its installation and maintenance require expertise that is not yet available
everywhere.
2. Unidirectional light propagation. Propagation of light is unidirectional. If we
need bidirectional communication, two fibers are needed.
3.Cost. The cable and the interfaces are relatively more expensive than those of
other guided media. If the demand for bandwidth is not high, often the use of
optical fiber cannot be justified.
Fiber-optic Cable

166. Table : Fiber types

167. Figure: Fiber construction

168. Figure: Fiber-optic cable connectors

169. Figure: Optical fiber performance

170. UNGUIDED MEDIA: WIRELESS
Unguidedmediatransportelectromagneticwaves
withoutusingaphysicalconductor.Thistypeof
communicationisoftenreferredtoaswireless
communication.
Radio Waves
Microwaves
Infrared
Topics discussed in this section:

171. Figure: Electromagnetic spectrum for wireless communication
UNGUIDED MEDIA: WIRELESS
•Unguidedmediatransportelectromagneticwaveswithoutusingaphysical
conductor.Thistypeofcommunicationisoftenreferredtoaswireless
communication.
•Figureshowsthepartoftheelectromagneticspectrum,rangingfrom3kHzto900
THz,usedforwirelesscommunication.

172. 1.Ground Propagation:
Radio waves travel through the lowest portion of the atmosphere, hugging the earth.
The low frequency signal follow the curvature of the planet.
Distance depends on the amount of the power.
Unguided signal can travel from the source to destination in several ways:
2.Sky Propagation:
Higher frequency radio radiate upward into the ionosphere where they arereflected back to
the earth.
Sky propagation allow for greater distance with lower power output.
3.line-of-sight Propagation:Very high frequency signals are transmitted in straight lines directly
from antenna to antenna.
Figure Propagation methods

173. Table: Bands

174. Figure: Wireless transmission waves

175. Radio Waves

176. Radio waves are used for multicast communications, such as radio and
television, and paging systems. They can penetrate through walls.
Highly regulated. Use omni directional antennas
Note
Radio Waves

177. Radio Waves

178. Microwaves

179. Microwaves

180. Microwaves are used for unicast communication such as cellular telephones,
satellite networks,
and wireless LANs.
Higher frequency ranges cannot penetrate walls.
Use directional antennas -point to point line of sight communications.
Note
Microwaves

181. Infrared

182. Infrared signals can be used for short-range communication in a closed area
using line-of-sight propagation.
Note
Infrared

183. Wireless Channels
Aresubjecttoalotmoreerrorsthanguided
mediachannels.
Interferenceisonecauseforerrors,canbe
circumventedwithhighSNR.
ThehighertheSNRthelesscapacityis
availablefortransmissionduetothe
broadcastnatureofthechannel.
Channelalsosubjecttofadingandno
coverageholes.

184. Switching
Connectivity
Wheneverwehavemultipledevices,wehavetheproblemofhowto
connectthemtomakeone-on-onecommunicationpossible.
Onesolutionistoinstallapoint-to-pointconnectionbetweeneachpair
ofdevices(meshtopology)orbetweenacentraldevice(hub)and
everyotherdevice(startopology).
However,thesemethodsareimpracticalandwastefulwhenappliedto
verylargenetworks.
Thenumberandlengthofthelinksrequiretoomuchinfrastructureto
becostefficient,andthemajorityofthoselinkswouldbeidlemostof
thetime.
InBustopology,thedistancesbetweendevicesandthetotalnumber
ofdevicesincreasebeyondthecapacitiesofthemediaandequipment.
Abettersolutionisswitching.

185. SwitchedNetwork
ASwitchednetworkconsistsofaseriesofinterlinkednodes,called
Switches.
Switchesaredevicescapableofcreatingtemporaryconnections
betweentwoormoredeviceslinkedtotheswitch.
Inaswitchednetwork,someofthesenodesareconnectedtothe
communicatingdevices(e.g.telephones).Othersareusedonlyfor
routing.
Switched Network

186. Switched Network
SwitchedNetwork
Longdistancetransmissionbetweendevicesistypically
doneoveranetworkofswitchingnodes.

187. Circuit Switched Network
Circuit-switchedNetwork
Circuitswitchingcreatesadirectphysicalconnectionbetweentwo
devicessuchasphonesorcomputers.
Acircuitswitchisadevicewithninputsandmoutputsthatcreatesa
temporaryconnectionbetweenaninputlinkandanoutputlink

189. Circuit Switched Network
AdvantagesofCircuitSwitching:
Thededicatedpath/circuitestablishedbetweensenderandreceiver
providesaguaranteeddatarate.
Oncethecircuitisestablished,dataistransmittedwithoutanydelayas
thereisnowaitingtimeateachswitch.
Sinceadedicatedcontinuoustransmissionpathisestablished,the
methodissuitableforlongcontinuoustransmission.
DisadvantagesofCircuitSwitching:
Astheconnectionisdedicateditcannotbeusedtotransmitanyother
dataevenifthechannelisfree.
Itisinefficientintermsofutilizationofsystemresources.Asresources
areallocatedfortheentiredurationofconnection,thesearenot
availabletootherconnections.
Dedicatedchannelsrequiremorebandwidth.
Priortoactualdatatransfer,thetimerequiredtoestablishaphysical
linkbetweenthetwostationsistoolong.

190. Packed Switched Network
PacketSwitching
Circuitswitchingwasdesignedforvoicecommunication.Inatelephone
conversation,forexample,onceacircuitisestablished,itremainsconnectedfor
thedurationofthesession.
1.Circuitswitchingislesswellsuitedtodataandothernon-voicetransmissions.
Non-voicetransmissionstendtobebursty;meaningthatdatacomeinspurt
withidlegapsbetweenthem.Whencircuit-switchedlinksareusedfordata
transmission,therefore,thelineisoftenidleanditsfacilitieswasted.
2.Asecondweaknessofcircuit-switchedconnectionsfordatatransmissionisinits
datarate.Acircuit-switchedlinkcreatestheequivalentofasinglecablebetween
twodevicesandtherebyassumeasingledatarateforbothdevices.
Thisassumptionlimitstheflexibilityandusefulnessofacircuit-switched
connectionfornetworksinterconnectingavarietyofdigitaldevices.
3.Third,circuitswitchingisinflexible.Onceacircuithasbeenestablished,that
circuitisthepathtakenbyallpartsofthetransmissionwhetheritremainsthe
mostefficient/availableornot.
Finally,circuitswitchingseesalltransmissionasequal.

191. Packet Switched Network
Packet-switchedNetwork
Whenacomputerattemptstosendafiletoanothercomputer,thefile
isbrokenintopacketssothatitcanbesentacrossthenetworkinthe
mostefficientway.

192. Packet Switched Network
ConnectionlessPacket-switchedNetwork
Eachpacketcontainscompleteaddressingorrouting
information(DestinationAddress,SourceAddress,Total
numberofpieces,Sequencenumber--writtenintheheader
sectionofpacket)

193. Packet Switched Network
Connection-orientedPacket-switchedNetwork
Datapacketsaresentsequentiallyoverapredefinedroute.(Fixedpath
betweenasourceanddestinationisestablishedpriortotransferofpackets.)
Packetsareassembled,givenasequencenumberandthentransportedover
thenetworktoadestinationinorder.
Inthismode,addressinformationisnotrequired.Thisisalsoknownas
virtualcircuitswitching.
The Process is
completed in 3 phases.
i.Connection
Establishment
Phase
ii.Data Transfer
Phase
iii.Connection
Release Phase

194. Packet Switched Network
AdvantagesofPacketSwitching:
EfficientuseofNetwork.
Easilygetaroundbrokenbitsorpackets.
CircuitSwitchingchargesuseronthedistanceanddurationofconnectionbut
PacketSwitchingchargesusersonlyonthebasisofdurationofconnectivity.
HighDataTransmissioninaPacketSwitchingisveryeasy.
AllthepacketsneednotfollowsamerouteinPacketSwitchingbutinCircuit
Switchingallthepacketsfollowsameroute.
PacketSwitchingusedigitalnetworkandenablesdigitaldatatobedirectly
transmittedtowarddestination.
DisadvantagesofPacketSwitching:
InPacketSwitchingPacketsarrivinginwrongorder.
TakesTransmissiondelay.
RequiresLargeamountRAM(RandomAccessMemory)tohandlelarge
amountofdatacommunicationinpackets.
SwitchingNodsrequiredmoreprocessionpowertoreconstructpackets
Packetsmaybelostontheirroute,sosequencenumbersarerequiredto
identifymissingpackets.

195. Message Switched Network
MessageswitchedNetwork
Messageswitchingisamethodinwhichthewhole
messageisstoredinaswitchandforwardedwhena
routeisavailable.

196. Message Switching
AdvantagesofMessageSwitching:
Efficienttrafficmanagement
Reducesnetworktrafficcongestion
Efficientuseoftransmissioncontrol
DisadvantagesofMessageSwitching:
Becauseofstoreandforward,transmissiondelay
Eachnoderequireslargecapacityforstoring.