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11Fundamentals of SS7and GSM protocolarchitecture and proceduresGiuliano Paris(TILS)email: giuliano.paris@telecomitalia.itRio de Janeiro, September 20052Outline Background on Signaling SS7 Characteristics and Protocol Architecture CCITT #7 Application Parts: TUP/ISUP and TCAP/ASEs GSM Protocol ArchitectureGSM radio channels (signaling and Traffic channel)GSM radio signaling channels (BCCH, RACH, etc)Examples of procedures (location update, handover, call scenario, roaming, SMS, etc.)23Some background on Some background on Signaling Signaling Signaling is defined as the exchange of informationspecifically concerned with the establishment, releaseand other control of calls, and network management, in automatic telecommunication operation (ITU definition). Channel Associated Signaling (CAS) A signaling method in which the signals necessary for the control of a single user channel (e.g. speech channel) are transmitted in the channel itself or in a signaling channel permanently dedicated to it. Common Channel Signaling (CCS) A signaling technique in which signaling information relating to a multiplicity of circuits, and other information such as that used for the network management, is conveyed over a single channel by addressedmessages.4CAS and CCS CAS and CCSUI UI UI UI S S S S1 2 3 .. M UI UI UI UI SCommonChannelUI = User InformationS= Signaling1 2 3 .. N 1 2 3 NChannel Associated Signaling (CAS)Common Channel Signaling (CCS)35CAS and CCS CAS and CCS In telephony CAS traditionally consisted of strictly necessary signals(very poor vocabolary) to handle a call (off-hook/on hook, calledparty number, dial tones and busy signals). It was defined forelectromechanical switching systems (based on selectors and xpoints). The subscriber dials '958' CAS is relatively slow (long call setup time), it offers a poverty of signals (messages) and no error detection and recovery for signalinginformation and finally it has been subjected to frauds. The introduction of electronic processors in the switching systems(SPC switches) and the development of data communictiontechniques and protocols have given the possibility to implement the concept of CCS (named CCITT #7, or CCS #7, or SS7). CCS #7 enables all the network element (i.e. SPC switches, network databases, etc.) to exchange signaling information in a reliable, fast, secure (protections from fraud), flexible (in terms of number of signals) and standardised (worldwide use) manner. 6CAS CAS signaling signaling Call CallSEIZURECASCASoff-hookfirst digitslast digitDIGITSPROCEED TO SENDSEIZUREringingoff-hookDIGITS PROCEED TO SEND on-hookANSWERCONVERSATIONon-hookCLEAR BACKCLEAR BACKdial tone.ADDRESS COMPLETE ADDRESS COMPLETERINGING TONEANSWERCLEAR FORWARD CLEAR FORWARDRELEASE GUARDRELEASE GUARDpostdiallingdelay47N12P. S.N12P. S.N12M. TransferN12M. TransferCCS linksignaling messagesspeech + signalingspeechFrom CHANNEL ASSOCIATED SIGNALING ....... To COMMON CHANNEL SIGNALING controlcontrol controlcontrol8Common Common Channel Channel Signaling Signaling Modes ModesSP SPSP SPSTPSpeech TrunksSignaling linkAssociated Mode Non Associated ModeSP= Signaling PointSTP= Signaling Transfer Point59CCS #7 CCS #7 Protocol Protocol Architecture Architecture MTP 1: Equivalent to OSI layer 1 (generally 64Kb/s) MTP 2: Error detection and recovery, flow control (basedon HDLC, equivalent to OSI layer 2 ) MTP 3: Provides message routing without lost or duplicated packets even in case of network failures or congestion (Equivalent to lower half of OSI layer 3)MTP Level 1MTP Level 2MTP Level 3USER PART USER PART10Contents Contents of of Recommendations Recommendations(Q.701 (Q.701- -Q.707) Q.707) relating relating to to the MTP the MTPRecommendation Q.701 contains a functional description and overview of the Message Transfer Part of SS No. 7.Recommendation Q.702 details the requirements of a signallingdata link to support SS No. 7.Recommendation Q.703 describes the signalling link functions.Recommendation Q.704 describes signalling network functionsand messages.Recommendation Q.706 defines and specifies values for MTP performance parameters.Recommendation Q.707 describes the testing and maintenancefunctions applicable to the MTP.611Circuit Circuit Related Related Applications Applications The signaling message coming from the USER Part (i.e. TUP) includes the related Circuit IdentificationCode- - IbF: IbF: prov|des prov|des messoges messoges ond ond procedures procedures regord|ng regord|ng te|ephone te|ephone co|| co||hond||ng hond||ng- - ISDN ISDN- -bF [or ISbF}: bF [or ISbF}: enr|ches enr|ches IbF IbF |eotures |eotures w|th w|th ISDN ISDN copob|||t|es copob|||t|es [ [beorer beorerserv|ces, serv|ces, supp|emetory supp|emetory serv|ces, serv|ces, such such os os co|||ng co|||ng ||ne ||ne |dent|||cot|on |dent|||cot|on, , etc etc.} .}MTP Level 1MTP Level 3MTP Level 2ISDN-UP/TUPTransportSessionPresentationApplicationPhysicalData LinkNetwork12MTP-2MTP-3ISUPTUP/ISUP MessageMSUISUPSwitch A Switch BThe messages originated froma switchs User Part (UP) are carried by the functional block MTP in a Message Signalling Unit (MSU) and delivered to the other switchs UP. MTP-3MTP-2MTP-1 MTP-1callcontrolcallcontrolCIC Signaling payload DPC OPCDPC: Destination Point CodeOPC: Originating Point CodeCIC: Circuit Identification Code713ABT(a)(b)Call Example with CCS (TUP/ISUP)speech trunksSignaling circuit(a) Calling party(b) Called partyswitch with SP and STP functionswitch with SP function14signaling regionASPSTPsignalinglinkQUADQUAD Model : non associated mode (stand-alone STP )speechsignaling regionB815Conceptual Conceptual models models: : transport transport and control and control networks networksswitchSPSPSPSPswitchswitchswitchSPswitchSTPSTP STPSTPSignalling NetworkTransport Network16Signalling Signalling data link data link : : level level 1 (MTP 1 (MTP- -1) 1) Level 1 defines the physical, electrical and functional characteristics of a signalling data link and the means to access it. The level 1 elementprovides a bearer for a signalling link. The standard channel time slot for the use of a signalling data link is time slot 16 (when available) in 2.048 Mbit/s digital path. The access to the signalling data link can be realized by a semipermanent connection through the switching network MTP-2MTP-3Switch BMTP-3MTP-22 Mb/s PCM path1616Switch ASwitch matrixMTP-1Switch matrix917SERVICE INDICATOR (SI)0000 Signalling network management messages0001 Signalling network testing and management messages0011 SCCP0100 Telephone User Part (TUP)0101 ISDN User Part (ISUP)0110 Data User Part (DUP).....F CK SIF SIO LIFIBFSNBIBBSN F8 16 8n (n>2) 4+4 2 6 1 7 1 7 8MSU (Message Signal Unit)Legenda:F = FlagCK = Check bits (CRC)SIF = Signalling Information FieldSIO = Service Indicator OctetLI = Length IndicatorFIB = Forward Indicator BitFSN = Forward Sequence NumberBIB = Backward Indicator BitBSN = Backward Sequence NumberSLS = Signaling Link SelectionUP MessagelabelroutingSI NIparts of interest to levels 3 and 4SLS OPC DPCSignalling Signalling link link functions functions: : level level 2 (MTP 2 (MTP- -2) 2)NETWORK INDICATOR (NI)00XX international network01XX spare for international network10XX national network11XX spare for national network18MTP MTP- -2 2 signal signal units units: FISU, LSSU, MSU : FISU, LSSU, MSULI Value Signal Unit Type0 Fill-In Signal Unit (FISU) 1..2 Link Status Signal Unit (LSSU) 3..63 Message Signal Unit (MSU)1019Signalling Signalling network network functions functions: : level level 3 (MTP 3 (MTP- -3) 3)MESSAGE DISTRIBUTION MESSAGEDISCRIMINATIONMESSAGEROUTINGMESSAGE HANDLINGSIGNALING NETWORK MANAGEMENTSIGNALINGTRAFFICMANAGEMENTSIGNALINGLINKMANAGEMENTMTP-3USER PARTSMTP-2Message FlowsControl and IndicationSIGNALINGROUTEMANAGEMENT20Signalling Signalling network network functions functions: : level level 3(MTP3): 3(MTP3):Signalling Signalling Traffic Traffic Management Management Procedures ProceduresChangeoverChangebackForced ReroutingControlled ReroutingSignalling Point RestartSignalling Traffic Flow Control1121SLS=XXX1SLS=XXX0A BAB D EF CXXX0XXX1SIGNALING TRAFFIC LOAD SHARING (I) SIGNALING TRAFFIC LOAD SHARING (I) Load sharing within a link setLoad sharing between link sets22SIGNALING TRAFFIC MANAGEMENT SIGNALING TRAFFIC MANAGEMENT( (Example Example of of changeover changeover) )1223SIGNALING ROUTE MANAGEMENT SIGNALING ROUTE MANAGEMENT(EXAMPLE: Transfer (EXAMPLE: Transfer Prohibited Prohibited Procedure ) Procedure )6131989STP sents a transfer prohibited message (TFP) to each of SPs. the message has the following information: Destination Point (DPC) = 6, 19, 13 Origin Point (OPC) = 9 Message Indication = TFP TFP related Destination = 8The 3 SPs (6,19,13), once received the TFP message, will execute a forcedrerouting procedureSTPi24MTP performance MTP performance requirements requirementsThe availability and dependability objectives for the transport of signalling messages by the MTP are: No more than one in 10E+7 (1 in 10,000,000) messages should be lost. No more than one in 10E+10 messages should be delivered out of sequence or duplicated. No more than one in 10E+9 message errors should remain undetected. The signalling route between an origination and destination SP should be available99.9998% of the times or better. This implies a maximum permissible downtime or unavailability of 10 minutes per year per route. Though there are no specific end-to-end delay objectives for SS7, they are specified forspecific services or uses of the SS7 protocol. Further there are delay objectives for some network components, and others can be calculated. Thus an estimate can be made forany given network configuration.1325Background: Background: What What is is ISDN? ISDN? It represents the evolution of the Integ