Understanding Network Monitoring and Physical Layer Basics

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

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

8. 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.

9. 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 )

10. 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.

11. 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

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

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

15. 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.

16. CoaxialCable

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

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

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

20. Twist inUTPcable

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

23. 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

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

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

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

27. FiberOpticCable Sideviewofasinglefiber. Endviewofasheathwiththreefibers.

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

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

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

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

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

33. Satellite

34. 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).

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

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

37. TelecommunicationNetworks

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

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

40. CircuitEstablishment

41. TelecommunicationNetworks

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

43. CircuitSwitchingexample

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

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

46. SharingaMedia:Multiplexing

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

48. UseofPackets

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

50. PacketSwitchingTechniques • Packetshandledintwoways • ▫ Datagram • ▫ Virtualcircuit