13. BSS:
TheBSSisthephysicalequipment thatprovidesradiocoverageto prescribed geographicalareas,known as thecells.It
containsequipment required to communicatewiththeMS.Functionally,aBSS consistsofacontrol functioncarried out bytheBSC
and atransmitting functionperformed by
theBTS.TheBTSistheradio transmissionequipment andcoverseachcell.ABSScan serveseveralcells
becauseit canhavemultipleBTSs.
TheBTScontainstheTranscoderRateAdapterUnit (TRAU).InTRAU,theGSM-specificspeech encoding and
decodingiscarriedout, aswellastherateadaptationfunctionfordata.Incertain situationstheTRAUis locatedat theMSC to
gainan advantageofmorecompressed transmissionbetweentheBTS and theMSC.
NSS:
TheNSSincludesthemainswitchingfunctionsof GSM,databasesrequired forthe subscribers,and mobility
management.Itsmain role isto managethecommunicationsbetweenGSM and other networkusers.
WithintheNSS,the switchingfunctionsareperformed bytheMSC.Subscriberinformationrelevant to
provisioningofservicesiskeptintheHLR.
TheotherdatabaseintheNSS istheVLR.
TheMSCperformsthenecessaryswitchingfunctionsrequiredfortheMSslocatedinan associated
geographicalarea,calledanMSC area
14. GSMIntroduction
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GSMInterfaces
TheRadioInterface(MS toBTS)
TheUmradio interface(betweenMSand basetransceiverstations[BTS])isthemost importantin anymobile
radiosystem, inthat it addressesthedemandingcharacteristicsoftheradio environment.
AbisInterface(BTStoBSC)
TheinterconnectionbetweentheBTS and theBSC isthroughastandard
interface,Abis(mostAbisinterfacesarevendorspecific).Theprimaryfunctions
carriedoverthisinterfacearetrafficchanneltransmission,terrestrialchannel management,and
radio channelmanagement.
AInterface(BSCtoMSC)
TheAinterfaceallowsinterconnectionbetweentheBSSradio basesubsystem
andtheMSC.ThephysicallayeroftheAinterfaceisa2-Mbps standard Consultative
CommitteeonTelephoneandTelegraph (CCITT)digitalconnection.