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    SynchronousDigitalHierarchySDH

    SynchronousDigitalHierarchy(SDH)

    SynchronousDigitalHierarchy(SDH)

    PlesiochronousDigitalHierarchy(PDH)

    SynchronousDigitalHierarchy(SDH)PrinciplesSDHstructureAccommodationofBitRatesforSDHUnificationofLowerTributariesofUS&CEPTUnificationofHigherTributariesofUS&CEPTAdaptationofSTMinSatellitesHigherOrderSTMInterfaceBetweenPDHandSDHWhatisJustificationFormationofTributaryUnitsSummaryofTributaryUnitFormation

    PathOverheadHigherOrderPathOverheadLowerOrderPathOverhead

    PointersFunctionsofaPointerOperationalPrinciplesofapointerPointerSummary

    SDHMajorOperationalComponentsSummaryofSDHManagementSectionsRegeneratorSectionOverheadMultiplexSectionOverhead

    SummaryofSDHMapping,Aligning,Pointerprocessing&Multiplexing

    ExamplesofSDHNetworksExamplesofLocalSDHNetworkExamplesofGlobalSDHNetwork

    2

    3

    55

    6121314161617171919

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    202027

    30313737

    38383940

    42

    4646247

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    SynchronousDigitalHierarchy(SDH)

    CharacteristicsCancombineEuropean&AmericanPDHBasicallybasedonSynchronousOpticalNETworkSONET(American)ThefollowingPDH(European)canbemultiplexed3

    4MultiplexingofPDHTributariestoSTM12(63)34(3)140(1)STM1SynchronousTransmissionMode1155.52Mbps

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    VariousCombinationsofPDHTributariestoSTM1

    2.048Mbps(63channels)or34Mbps(3channels)or140Mbps(1channel)willformanSTM1.n1of2.048Mbps,n2of34Mbpscanbemultiplexedwheren1&n2willgiverisetoatotaloflessthan155.52Mbps;ifn2=2,n1(max)=21

    n2=1,n1(max)=42

    5

    PlesiochronousDigitalHierarchy(PDH)-Principles

    Basicbitperiodshrunkateachpointfrom2Mbpsupwards(multiplexing)andateachmultiplexingpointbitsareadded.Example:

    SpeedBitPeriodAddedbits(assume)2Mbps488ns8Mbps118nsx34Mbps25nsx1140Mbps7nsx2560Mbps1.7nsx3

    6

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    7ThePrinciplesofPDH2Mbps2/82/8AddbitstointroduceSYN8140Mbps34Mbps8MbpsAddbitstointroduceSYN34AddbitstointroduceSYN140RemovebitstoverifySYN8RemovetotoverifySYN34RemovebitstoverifySYN140DEMULTIPLEXINGMULTIPLEXING34/1408/3434/1408/34

    xxxxxxxxxxxx2Mbps2/82/8AddbitstointroduceSYN8140Mbps34Mbps8MbpsAddbitsto

    introduceSYN34AddbitstointroduceSYN140RemovebitstoverifySYN8RemovetotoverifySYN34RemovebitstoverifySYN140DEMULTIPLEXINGMULTIPLEXING34/1408/3434/140

    8/34xxxxxxxxxxxxAteachde-multiplexingpointbitperiodexpands,andtheinsertedbitsareremoved

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    Hencefromexample,560Mbpsstream,an8Mbpsstreamcannotbeobtaineddirect.560Mbpshastobeconvertedto140Mbps,thento34Mbps,andthento8Mbps;duetotheextractionofoverheadbitsateachde-multiplexingpoint.PDHmeansPlesiochronousdigitalHierarchy.PlesiochronousmeansMultiplesynchornization.Thatiswhytheabovecannotbeachieved.8

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    9SynchronousDigitalHierarchy(SDH)-Principles2Mbps(n1)34Mbps(n2)140Mbps(n3)155.52Mbps(6.4ns)(488ns)25ns)(7ns)2Mbps(n1)34Mbps(n2)140Mbps(n3)155.52Mbps(6.4ns)(488ns)25ns)(7ns)Differentperiodsofbitsaremultiplexedtoformasingleperiodof6.4nsSimilarly,from6.4nsdifferentperiodscanbeobtainedatde-multiplexingpoints

    Alltreatmentwillbedoneattheentrancefrom2Mbps,34Mbpsor140MbpsintoSTM1NoadditionalbitsareintroducedwithinSTM1(afterentrance)transformingfrom2Mbpsor34Mbpsor140MbpstoSTM110

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    PDHtoSDHattheEntry

    SDHisalwaysofhigherfrequencythanPDH.ThetreatmenttothedeviationofthePDHstreamshastobeaccommodatedintheSDHstream.ComplexityincreaseswhenthehigherorderPDHstreamtobeplacedintheSDHstream.Hencepositive,negative&zerojustificationtobeapplied,dependinguponthePDHstreamattheentrytoSDH.ManagementofPDHtributary(bitstream)throughoutSDHandbackagaintode-multiplextoPDHThismanagementinformationiscalledpathOverhead(POH).Exchangeatwhichthistributarytobeterminated,errorcontroletc.AttheentrytoSDHstream,anyPDHtributarywillbetreatedforpositive,negative&zerojustification,dependingupontheprimaryPCMscharacteristics.POHandstuffingbitstoconverttoasinglebitperiodof6.4ns.Afterthisnoadditionalbitsareintroducedtofurthershrinktheperiodof6.4ns.EveninhigherorderSDH,assumeSTM4,noadditionalbitsintroduced.InSTM4thebitperiodexactly(6.4ns)/4=1.6ns

    SameconceptextendsforhigherorderSTM.11

    SDHstructure

    BasicStructureIn125s,2430words,eachwordrepresent8bitswhichisequivalenttoasample.Hencefor1secondthereare155.52Mb.Usesword(byte)interleaving.Henceeasytomanage.Inordertoanalyze

    thestructurethese2430wordsareorganizedin9rowswith270columnsasfollows:12

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    BasicStructure

    123456789

    12270271216021612430

    125s125s

    2430x8bits

    13

    1s

    155.52MbitsStructurefor2Mbpsand34Mbps

    2.048Mbps34.368Mbps1234

    56789

    12345..............................................

    ......3233343536

    12......838485..................................................................................

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    ..............

    ..........755756

    125s=>36x8125s=>756x8

    1s=>2304kb1s=>48.384kb

    Sparebits=0.256(12.5%)Sparebits=14.02(40%)

    Furtherreviewedonslide#15

    Sparebits=PathOverhead+justification

    14

    For34Mbpsstructure21Nos.2.048Mbpscanbeplaced

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    Observations

    For34MbpsinPDH2.048Mbps,16streamscanbemultiplexedInSDH21Nos.canbemultiplexed,WHY?ForPDH,CEPT34.368MbpsandPDHAmericanequipmentis44.736Mbps,Hence84columnsareusedfor44.736MbpsAmericansystem,SDHstreamstemsfromAmericanSONET.(CEPTCommitteeofEuropeanPost&Telecommunication)

    HenceithasbeendesignatedforAmerican44.736Mbps,thoughweareusingitforCEPT34Mbps.Thatswhytherearemanysparebitsifweuseitfor34MbpsdirectlyonSTM1.15

    Structureof34Mbpswhenformedfrom2Mbps

    (Actual34.368Mbps)

    1234

    56789

    12......838485......................................................................................................755756

    1

    2........84

    For125s=>756x8bits1s=>48384

    16

    SparebitsforPOH+Justification=9.3444(6.7%)

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    Structureof34MbpsinSTM1whenformedfrom34Mbpsitself

    EverybasictributaryhastoaccommodateforeachPOH+JustificationHencefor34directtobeplaced,itneedstwomorecolumnstoaccommodatePOH+Justification12........86

    Ifwefillwith21Nos.of2.048Mbps,thesefirsttwocolumnsarespare

    17

    Structureof140MbpsinSTM1whenformedfrom34Mbps

    (Actual139.264Mbps)

    1234

    56789

    12......257258259....................................................................

    ..........................14641465........23212322

    1

    2........258

    For125s=>2322x8bits1s=>148.605

    18

    SparebitsforPOH+Justification=9.3444(6.7%)

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    Observations

    For140MbpsisPDH(CEPT)thereare4Nos.34Mbpsstreams.ButinSDHonly3Nos34Mbpscanbeaccommodated63Nos2.048MbpscanbeaccommodatedinSDH.NoequipmentforPDH140Mbps(America)19

    Structureof140MbpsinSTM1whenformedfrom140Mbpsitself

    Similarreasoningasfor34Mbps,inordertodirect140MbpsintoSDH,Onemightthinkthat3columnsareusedforPOHandIfwefillwith3of34Mbps,thesefirst3columnsarespare

    20

    10

    Justification,butitisnot.Why?261260......4321

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    BytesAllocatedforJustificationandMatchingthespeedvariationsinputtributaries

    WhenweconsiderTU12,12.5%bitsareavailableformatchingthevariationsaswellasforjustification.ForsimilarvariationsTU340.0%bitsareavailableButorsimilarvariationsinTU4,ifweuse258columns6.7%bitsareavailable,whichisnotenoughwhenweconsiderthebitspeed.Hence2morecolumnsarekeptforthetreatmentofvariationsin140Mbpsaswellasjustification(tobeadjusted).Hencethereisadeviationfromthepreviousthinkingand260columnsareallocatedfor140Mbpsinsteadof258columns.OnemorecolumnisallocatedforPOHandforthePointerfirst9bytesofthe4thRowisallocated.21

    Structureof140MbpsinSTM1whenformedfrom140Mbpsitself

    Additional3columnsare

    1234......260261

    Ifwefillwith3of34Mbps,thesefirst3columnsarespare

    22

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    23AccommodationofBitRatesforSDHManagementforRepeaterOverhead(RSOH)seeslide#77d.combinationofa&b*orc.140Mbps1No.orb.34Mbps3Nosora.2.048Mbps63NosMaximumofPointerforVC-4seeslide#60*if,1Noof34Mbpsthenamaximumof42Nos.of2Mbpsor2Nosof34Mbpsthenamaximumof21Nos.of2Mbps12709MultiplexSectionOverhead(MSOH)seeslide#77

    d.combinationofa&b*orc.140Mbps1No.orb.34Mbps3Nosora.2.048Mbps63NosMaximumofPointerforVC-4seeslide#60*if,1Noof34Mbpsthenamaximumof42Nos.of2Mbpsor

    2Nosof34Mbpsthenamaximumof21Nos.of2Mbps12709MultiplexSectionOverhead(MSOH)seeslide#77BuildingblocksofSTM1

    2MbpsisthelowestspeedforEuropeansystemtobeconnectedtoSTM1Then34Mbpsand140Mbpssystemscanbeconnected

    8MbpscannotbeconnectedtoSTM1STM1canbemadeeitherfrom140Mbpsoracombinationof2Mbpsand34Mbps.HencethebasicbuildingblockhasbeendesignedtoaccommodatetheabovethinkingTUisthebasicbuildingblockofSDH,fromPDHfor2Mbpsor34MbpsTU12=2Mbps

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    TU3=34MbpsIntermediatemultiplexingpointhasbeencreatedtoaccommodateAmericansystems.24

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    PDH

    Thereare3standardsintheworld:CEPT.NorthAmericaandJapan.SDHcancombineallthese3systemsexceptCEPT8.448MbpsandJapan32.064Mbpsand97.728Mbps