1 / 76

Chapt er 3

Chapt er 3. P hysica l Layer. P hysica l Lay er. The Ph y si c a l la y e r i s re s po n sib l e for t h e ulti m at e t ra n s m is s io n of dat a o v e r netwo r k c o mmunications media.

christopherr
Download Presentation

Chapt er 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter3 PhysicalLayer

  2. PhysicalLayer • The Physical layer is responsible for the ultimate transmission of dataovernetworkcommunicationsmedia. • It operates with data in the form of bits that are sent from the Physical layer of the sending (source) device and received at the Physicallayerofthedestinationdevice. • The physical layer provides an electrical, mechanical, and proceduralinterfacetothetransmissionmedium. • Ethernet cabling, Token Ring network technology and SCSIall • functionatthePhysicallayeroftheOSImodel. • Hubs and other repeaters are standard network devices that functionatthePhysicallayer.Cablesandconnectorsalsoareapart of the Physical layer. At the Physical layer, data are transmitted usingthetypeofsignalingsupportedbythephysicalmedium: • Electricvoltages • Radiofrequencies • Pulsesofinfraredorordinarylight

  3. Physical Layer • Guided Media: Copper, Fiber Cabling and its capacity standards • Unguided Media: Bluetooth, Wi-Fi/Wireless LAN, Satellite Communication Basics(Microwave, Radio waves). • Circuit/Packet/Message Switching. • ISDN Signaling & Architecture. • Network Performance: Bandwidth, Throughput, Latency, Bandwidth-Delay Product, Jitter.

  4. NetworkMonitoring • Networkmonitoringreferstothepracticeofoverseeingtheoperationofacomputernetworkusingspecializedmanagementsoftwaretools. • Networkmonitoringsystemsareusedtoensureavailabilityandoverallperformanceof computers(hosts)andnetworkservices. • ThekeyfeaturesofNetworkMonitoringSystemare: • Delay • Latency • Throughput

  5. Delay • Asapackettravelsfromonenode(hostorrouter)tothesubsequentnode(hostorrouter)alongthepath,thepacket suffersfromseveraldifferenttypesofdelaysateachnodealongthepath. • Themostimportantofthesedelaysarethe • Nodalprocessingdelay/ProcessingDelay • Queuingdelay • Transmissiondelayand • Propagationdelay

  6. Delay • Nodalprocessingdelay/ProcessingDelay • Thetimerequiredtoexaminethepacket'sheaderanddetermine wheretodirectthepacketispartoftheprocessingdelay. • Theprocessingdelaycanalsoincludeotherfactors,suchasthe time needed to check for bit-level errors in the packet that occurredintransmittingthepacket'sbitsfromtheupstreamrouter torouter.

  7. Queuingdelay • After this nodal processing, the router directs the packet to the queuethatprecedesthelinktorouterB. • Atthequeue,thepacketexperiencesaqueuingdelayasitwaits tobetransmittedontothelink. • Thequeuingdelayofaspecificpacketwilldependonthenumber of other, earlier-arriving packets that are queued and waiting for transmissionacrossthelink; • Thedelayofagivenpacketcanvary significantlyfrompackettopacket. • If the queue is empty and no other packet is currently being transmitted,thenourpacket'squeuingdelayiszero.

  8. Delay • TransmissionDelay • The amount of time required to transmit all of the packet's bits intothelink. • ItisthetimetoputM-bitmessage in the wire. • T-delay=M(bits)/Rate(bits/sec)=M/Rseconds • PropagationDelay • The time required to send packet from one router to another router.Thebitpropagatesatthepropagationspeedofthelink. • The propagation speed depends on the physical medium of thelinkandthedistancefromsourcetodestination. • P-delay=Length/speedofsignals=Length/⅔c=Dseconds • TotalDelay • TotalDelay dtotal=dproc+dqueue+dtrans+dprop • IfthereisNnodeandallthedelaysaresamethenthetotaldelayis TotalDelay dtotal =N(dproc+dqueue+dtrans +dprop )

  9. Latency • Measuresoftimedelayexperiencedinasystem. • One-waylatencyfromsourcetodestinationplustheone-waylatencyfromthedestinationbacktothesource. • A Low Latency network connection is one that generally experiences small delay times, while a high latencyconnectiongenerallysuffersfromlongdelays. • LatencyExample:(L=D+M/R) • ▫ Dialup withatelephonemodem: • D=5ms,R=56kbps,M=1250bytes • L=5ms+(1250x8)/(56x103)sec=184ms • ▫ Broadbandcross-countrylink: • D=50ms,R=10Mbps,M=1250bytes • L=50ms+(1250x8)/(10x106)sec=51ms • Alonglinkoraslowratemeanshighlatency.

  10. Throughput • Bandwidthdefinesasthenetbitratecannelcapacityorthemaximumthroughputofachannel. successful • Whereasthroughputistheaveragerate of • messagedeliveryoveracommunicationchannel. • Measuredinbits/second. • Units • ▫ Kbits/sec=103 bps • ▫ Mbits/sec=106 bps • ▫ Gbits/sec=109 bps • ▫ Tbits/sec=1012 bps

  11. NetworkCables • Coaxial • ▫ ThickEthernet • ▫ ThinEthernet • Twistedpairs • ▫ Shieldedtwistedpair • ▫ Unshieldedtwistedpair • CAT3:datarateupto10Mbps(Ethernet) • CAT4:datarateupto20Mbps(TokenRing) • CAT5:datarateupto100Mbps(FastEthernet) • CAT5e:datarateupto1000Mbps(GigabitEthernet) • CAT6:datarateupto10Gbps(GigabitEthernet) • FiberOptics

  12. CoaxialCable • Coaxialcableisatypeofshieldedcable. • It consistsofasolidcopperconductor surroundedby insulatingmaterialandabraidedconductiveshield. • In LANapplications, thebraidedshieldingiselectrically theinnerconductorfromexternal grounded toprotect • electricalnoise. • Theshieldalsokeepsthetransmittedsignalconfinedtothecable,whichreducessignalloss. • Thishelpsmakecoaxialcablelessnoisythanothertypesof coppercabling,butalsomakesitmoreexpensive. • Theneedtogroundtheshieldingandthebulkysizeofcoaxial cablemakeitmoredifficulttoinstallthanothercopper cabling.

  13. CoaxialCableTypes • ThickEthernet: ThickEthernetisalsocalled10BASE5cablewhichisof50ohm.10 represents the data rate transfer which is 10Mbps and the last number5representsthemaximum length which is 500m with out using the repeaters. You can extend the cable by using the repeaters. • ThinEthernet: ThinEthernetisalsocalled10BASE2cablewhichisof50ohm.10 represents the data rate transfer which is 10Mbps and the last number 2 represents the maximum length which is 200m with out using the repeaters. You can extend the cable by using the repeaters.

  14. CoaxialCable

  15. TwistedPair • Whenwiresaretwistedtogether,twistsreducethecable’ssensitivitytooutsideEMI. • Twistedpaircablesareconstructed of multiple pairs of twisted cables contained by common jackets. • Twistedpairoftwotypes • Shieldedtwistedpair • Unshieldedtwistedpair

  16. UnshieldedTwistedPair(UTP) • UTPcontainsnoshieldingandismoresusceptibletoexternal noisebutisthemostfrequentlyusedbecauseitis inexpensiveandeasiertoinstall. • Thecablehasfourpairsofwiresinsidethejacket. • Eachpairistwistedwithdifferentnumberoftwistsperinchto helpeliminateinterfacefromadjacentpairsandother electricaldevices. • The higherthetwistperinchhigherthesupported • transmission.

  17. UTP • TypesofUTP • ▫ CAT3:datarateupto10Mbps(Ethernet) • ▫ CAT4:datarateupto20Mbps(TokenRing) • ▫ CAT5:datarateupto100Mbps(FastEthernet) • ▫ CAT5e:datarateupto1000Mbps(GigabitEthernet) • ▫ CAT6:datarateupto10Gbps(GigabitEthernet) • Maximumcablelengthwithoutrepeater100m

  18. Twist inUTPcable

  19. UTPCableColorCoding • CablingStandards(usedforUTP): • EIA/TIA568Acolorcoding: • EIA/TIA568Bcolorcoding: gGoBbObrBroOgBbGbrBr • Where • ▫ g-lightgreenorStrippedgreen(wire) • ▫ G-SolidGreen(wire) • SimilarForotherwireaswell.

  20. UTP Cable Types . • Straight through Cable: • A-A or B-B setting, • used to connect different layer device, • e.g. hub to computer. • Cross-over Cable: • A-B or B-A setting, • used to connect same layer device, • e.g. computer to computer, router to computer

  21. ShieldedTwistedPair • STPcablecontainsanouterconductiveshieldthatis electricallygroundedtoinsulatethesignalsfromexternal electricalnoise. • STPalsousesinnerfoilshieldstoprotecteachwirepairfromnoisegeneratedbytheotherpairs. • ThusShieldedtwistedpairissuitablefortheenvironmentswithelectricalinterference;however,theextrashieldingcanmakethecablesquitebulkyaswellasbitexpensive.

  22. FiberOpticCable • Fiber-opticcableincreasesanddecreasestheintensityof lighttorepresentbinaryonesandzerosindata transmissions. • Thestrengthofalightsignaldoesnotdiminishasmuchasthestrengthofanelectricalsignaldoesoveranidenticalrun length. • Opticalsignalsarenotaffectedbyelectricalnoiseandoptical fiberdoesnotneedtobegroundedunlessthejacketcontains ametalorametalizedstrengthmember. • Therefore,opticalfiberisoftenusedbetweenbuildingsand • betweenfloorswithinabuilding. • Ascostsdecreaseandspeedsincrease,opticalfibermaybecomeamorecommonlyusedLANmedia.

  23. FiberOpticCable • Led orlaserusedasthelightsourceintheOpticalfiberfor transmittingtheopticalfiber. • Signalsreceivedbyphotodiodes,solidstatedevicesthat • detectthevariationsinlightintensity. • BandwidthintherangeoftheGbps. • Types: • ▫ SingleMode:forlongerdistanceandLASERisusedas lightsource. • ▫ MultiMode:forshorterdistanceandLEDisusedaslight source.

  24. FiberOpticCable Sideviewofasinglefiber. Endviewofasheathwiththreefibers.

  25. Line-of-sitePropagation • Line-of-sightpropagationreferstoelectro-magneticradiation oracousticwavepropagation. • Electromagnetictransmissionincludeslightemissions • travelinginastraightline. • Theraysorwavesmaybediffracted,refracted,reflected,or absorbedbyatmosphereandobstructionswithmaterialandgenerallycannottraveloverthehorizonorbehindobstacles. • Inwirelesschannels,notonlydoesradiationlossoccur,butalsooneantennamaynot"see"anotherbecauseoftheearth'scurvature.

  26. Satellites • GeostationarySatellites • Medium-EarthOrbitSatellites • Low-EarthOrbitSatellites

  27. GeostationarySatellites • Ataltitudeapprox.36000Kmaboveequatorialplane,satellite rotationperiodis24hrs. • SatelliteisstationarywithrespecttoEarth. • Withcurrenttechnology,itisunwisetohavegeostationary satellitesspacedmuchcloserthan2degreesinthe360- degreeequatorialplane,toavoidinterference. • Withaspacingof2degrees,therecanonlybe360/2=180of thesesatellitesintheskyatonce. • However,eachtranspondercanusemultiplefrequenciesandpolarizationstoincreasetheavailablebandwidth.

  28. Medium-EarthOrbitSatellites • Atmuchloweraltitudes,betweenthetwoVanAllenbelts,wefindtheMEO(Medium-EarthOrbit)satellites. • Asviewedfromtheearth,thesedriftslowlyinlongitude, takingsomethinglike6hourstocircletheearth.Accordingly, theymustbetrackedastheymovethroughthesky.Because theyarelowerthantheGEOs,theyhaveasmallerfootprint onthegroundandrequirelesspowerfultransmitterstoreachthem. • GPS(GlobalPositioningSystem)satellitesorbitingatabout 18,000kmareexamplesofMEOsatellites.

  29. Low-EarthOrbitSatellites • Movingdowninaltitude,wecometotheLEO(Low-Earth Orbit)satellites. • Duetotheirrapidmotion,largenumbersofthemareneeded • foracompletesystem. • Ontheotherhand,becausethesatellitesaresoclosetotheearth,thegroundstationsdonotneedmuchpower,andtheround-tripdelayisonlyafewmilliseconds.

  30. Satellite

  31. Multiplexing • In telecommunications andcomputer networks, multiplexingisa methodbywhichmultiple analog message signalsordigital data • streamsarecombinedintoonesignaloverasharedmedium. • Theaimistoshareanexpensiveresource.Forexample,in telecommunications,severaltelephonecallsmaybecarriedusingonewire.Multiplexingoriginatedintelegraphy,andisnowwidelyappliedincommunications. • Themultiplexedsignalistransmittedoveracommunicationchannel,whichmaybeaphysicaltransmissionmedium. • Themultiplexingdividesthecapacityofthehigh-levelcommunication channelintoseverallow-levellogicalchannels,oneforeachmessagesignalordatastreamtobetransferred. • Areverseprocess,knownasdemultiplexing,canextracttheoriginalchannelsonthereceiverside. • Adevicethatperformsthemultiplexingiscalledamultiplexer(MUX),andadevicethatperformsthereverseprocessiscalledademultiplexer(DEMUX).

  32. Switching • Multiplexingisdonetomaximisetheuseofacommunications channel.Butswitchingisthemanipulationoftheendsofthecommunicationschannel. • Longdistancetransmissionistypicallydoneoveranetworkof • switchednodes. • Nodesnotconcernedwithcontentofdata. • Enddevicesarestations,computer,terminal,phone,etc. • A collectionofnodesandconnectionsisacommunicationsnetwork. • Dataroutedbybeingswitchedfromnodetonode.

  33. Nodes • Nodesmayconnecttoothernodesonly,ortostationsandothernodes • Nodetonodelinksusuallymultiplexed • Networkisusuallypartiallyconnected • Someredundantconnectionsaredesirableforreliability • Twodifferentswitchingtechnologies • ▫ Circuitswitching • ▫ Packetswitching

  34. TelecommunicationNetworks

  35. TelecomsComponents • Subscriber • ▫ Devicesattachedtonetwork • Subscriberline • ▫ LocalLoop • ▫ Subscriberloop • ▫ Connectiontonetwork • ▫ Fewkmuptofewtensofkm • Exchange • ▫ Switchingcenters • ▫ Endoffice-supportssubscribers • Trunks • ▫ Branchesbetweenexchanges • ▫ Multiplexed

  36. StructureofTelephoneSystem • Localloops • Analogtwistedpairsgoingtohousesandbusinesses • Trunks • Digitalfiberopticsconnectingtheswitchingoffices • Switchingoffices(Exchanges) • Wherecallsaremovedfromonetrunktoanother

  37. CircuitEstablishment

  38. TelecommunicationNetworks

  39. CircuitSwitching • Dedicatedcommunicationpathbetweentwostations • Threephases • ▫ Establish • ▫ Transfer • ▫ Disconnect • Must haveswitchingcapacityandchannelcapacitytoestablishconnection • Musthaveintelligencetoworkoutrouting

  40. CircuitSwitchingexample

  41. CircuitSwitching • Switchesaresetupatthebeginningoftheconnectionand maintainedthroughouttheconnection • Networkresourcesreservedanddedicatedfromsenderto receiver • Expensive(ChargingBasedperminute) • Needactualconnection • LowLatency • EachPacketfollowssamepath. • Bandwidthavailableisfixed. • Notavery efficientstrategy.Aconnectionholds a physicallineevenduringsilenceperiods(whenthereisnothingto transmit) • Developedforvoicetraffic(phone)

  42. SharingaMedia:Multiplexing • Multiplexingmeanscombiningdifferentstreamsintojustonecommunicationline. • Multiplexingincircuitswitching: • ▫ Frequency-DivisionMultiplexing • ▫ Time-DivisionMultiplexing

  43. SharingaMedia:Multiplexing

  44. PacketSwitchingPrinciple • Circuitswitchingdesignedforvoice • ▫ Resourcesdedicatedtoaparticularcall • ▫ Muchofthetimeadataconnectionisidle • ▫ Datarateisfixed • Bothendsmustoperateatthesamerate • In Packet Switching, packets are received, stored briefly (buffered) andpastontothenextnode. • Datatransmittedinsmallpackets • Controlinfo • ▫ Routing(addressing)info

  45. UseofPackets

  46. Advantages • Lineefficiency • ▫ Singlenodetonodelinkcanbesharedbymanypacketsovertime • ▫ Packetsqueuedandtransmittedasfastaspossible • Datarateconversion • ▫ Eachstationconnectstothelocalnodeatitsownspeed • ▫ Nodesbufferdataifrequiredtoequalizerates • Packetsareacceptedevenwhennetworkisbusy • ▫ Deliverymayslowdown • Prioritiescanbeused

  47. PacketSwitchingTechniques • Packetshandledintwoways • ▫ Datagram • ▫ Virtualcircuit

More Related