Signalling

SignallingOleksandr KosovskyyNetwork architecture

AbisAbisAGbGsFGfCEGdGcGsNcMcMcDGrGnHGiInternet(PSPDN)PLMN/ PSTN

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CCS7 Protocol Stack vs.the OSI Reference ModelPhysical layerData link layerNetwork layerTransport layerSession layerPresentation layerApplication layerMTP (levels 1-3)User Part

(Common part)(PSTN, ISDN, GSM)

User PartOSI Reference ModelCommon Channel Signalling No. 7Application Part

(GSM specific part)SCCPLayer1234567Level1234CCS7 in GSM NetworkMSC/VLRHLR/EIR/AUCPSTNExchangeBSCMAP / INAPTCAPSCCPMTPBSSAPMAP/INAPTCAPSCCPMTPTUPISUPSCCPMTPBSSAPSCCPMTPTUPISUPM3UA vs. MTP3MAP/INAPTCAPSCCPMTPISUPMAP/INAPTCAPSCCPM3UABICCISUPMTP (levels 1-3)User PartApplication PartSCCPThe ISUP Message StructureCICOPCDPCLabelUser dataISUPMessageLabelStructureSLS 12bits 4bits 14 or 24 14 or 24 bits8n bits24=16 SLC per SPCExample of an ISUP Connection

X0D0D20VMSC/VLRPSTNexchange-APSTNexchange-B

Setup (Dialled number)Process Informationand make connectionSetup (Ringing)ConnectConversationIAM(CIC+dialled digits)IAM (CIC+dialled digits)ACM (CIC)ACM (CIC)AlertANM (CIC)ANM (CIC)ConnectApplication partAll application parts which use services provided by SCCP level can be called as SCCP subsystems or SCCP users.For example, SCCP subsystems areBSSAP base station subsystem APMAP Mobile APINAP Intelligent network APCAP Customized Applications for Mobile networks Enhanced Logic APSCCPBSSAPMAP / INAPTCAPMTPApplication partSCCPBSSAPMAP / INAPTCAPMTPBSSAPBSSMAP DTAP

BSCMSDTAP (Call setup, location update)BSSMAP(Paging)In BSSAP both circuit-related and non-circuit relatedsignalling messages required so SCCP handle CO and CL messages NOKIA TELECOMMUNICATIONS SSPSCPInitialDP : used to start dialogue between SSP and SCPReleaseCall : SCP instructs SSP to release a callIn INAP/CAP only non-circuit related signalling messagesMTPSCCPTCAPMAP-MMAP-VMTPSCCPTCAPMAP-HMAP-EMSC/VLRHLR/AUC/EIROSI(level)1- 2374-6In MAP non-circuit related signalling messages requiredMSS Interfaces & ProtocolsBSSAP for radio access controlBICC for bearer independent call controlISUP for TDM trunk call control All above SS7 signaling over SIGTRAN via MGWH.248 for MGW control (GCP)

MSCServerTDMH.248ATM, IPMSCServerMcMGWNcAAL2/AAL5ATMNbMcSigtranIPBICC, ATM/IPHLR ServicesMAPCAPMGWRTPIP PSTNSS7BSCSigtranIPATDMBSSAPH.248ATM, IP10Signalling routingMTPSCCPSignalling messages from upper level2.by SCCP1.by MTPto other network elementsRouting by MTPLevel 1Physical ConnectionsMessageTransferPart (MTP)Signalling Message HandlingLevel 2Data Link ControlLevel 3MessageSignal unitBitData unitFunctions of MTP Level 2 and Level 3Are thereany errors?MSUNoMessage handlingNetwork ManagementAre thereany errors?LSSUYesYesError handlingNoLevel 2Level 3ISUPSCCPNetwork management messagesTo othernetworkelementMessage Handling in MTP Level 3

DiscriminationDPC = own SPCRoutingDistributionDPCown SPCNetwork ManagementSCCPISUPMTP usersFrom MTP level 2To MTP level 2Signalling MessageHandlingStructure of Messages from MTP UsersFCKSIFSIOLIFIBFSNBIBBSNFFirst bittransmitted 8 16 8n, n>2 8 2 6 1 7 1 7 8User DataSIOSIOSIODPCOPCSLCUser DataDPCOPCSLSUser DataDPCOPCSLSCICSIOUser DataDPCOPCCICTUPISUPNetwork ManagementSCCPSLSOPCDPCOPC Originating Point CodeDPC Destination Point CodeSLS Signalling Link SelectionUser informationsubfieldLabelDCBASubservicefieldDCBAServiceindicator(SI)Signalling Information Field (SIF)Service informationoctet (SIO)First bittransmitted4 bits 14 bits 14 bits 4bits 4 bitsRouting label0000-0011 : IN00100-0111 : IN11000-1011 : NA01100-1111 : NA10000 : SNM0001 : SNT0011 : SCCP0100 : TUP0101 : ISUPRouting by MTPDiscriminationDPC = own SPCRoutingDistributionISUP in MSCIAM (DPC,CIC)ISUPMTPISUP in PSTNIAM (DPC,CIC)X0D0D20MSC/VLRPSTNexchange-AIAM (CIC+dialled digits)DPCSIO = ISUPSCCP routingBasicConnectionlessServiceSequencedConnectionlessServiceBasicConnection-orientedServiceFlow ControlConnection-orientedServiceConnectionlessServicesConnection-orientedServices0123Services provided by the SCCPProtocol ClassWho are users of SCCP? Why these three application parts need SCCP service?Application LevelSCCP LevelBSSAP/RANAPMAPINAP/CAPConnection orientedServicesConnectionlessServicesSignalling Routing (MTP and SCCP)

BSSAPMAPINAPRI = GTApplication partsSCCPMTPSIO = SCCPGT AnalysisOther DPCDiscriminationDPC = own SPCRoutingDistributionDPC is not own SPCRIRI = SSNDPCOwn SPCSSNGlobal Title AnalysisGT analysis is used to analyze a GT to find out the destination of the signalling message. GTAnalysis Numbering Plan DigitsDPCRIWhen the DPC receives the message RI = SSN, there is no need for GT analysis. RI = GT, the GT analysis has to be performed.Example of SCCP Routing on GTInternational Roaming, the first location update MS sends IMSI to the VLR in VPLMN VLR will send "update location" message to HLR Does the VLR know SPC of the HLR? Does the VLR know HLR address? How can the VLR send LU message to the HLR?

IMSIAnalysisIMSI or E.212Hybrid no. or E.214GTAnalysisMessage handlingSCCP routing on GTMTPIMSI analysisIMSIAnalysisIMSI or E.212Hybrid no. or E.214MCCMNCMSINOperator No.MSINSSNIn fact on one GSM node can handled more then one Application Level easiest way to access with c7 messages to correct Application is GT.SubSystemNumber strictly defined access to AP. For example:6 HLR (MAP) 7 VLR (MAP) 8 MSC (MAP) 9 EIR (MAP)146 CAP