Reference (1/2) [1] Wireless and Mobile Network Architectures Y-Bing Lin and Imrich Chlamtac Wiley Computer Publishing Chapters 2 and 5 [2] [3] Teleph

Transcription

1 Signaling System No7 -SS7 1 Signaling System No 7 (Signaling System 7; SS7) AMPS GSM SS7 SS7 SS7 GSM 3G SS7

2 Reference (1/2) [1] Wireless and Mobile Network Architectures Y-Bing Lin and Imrich Chlamtac Wiley Computer Publishing Chapters 2 and 5 [2] [3] Telephone Network and PBX Software Yi- Bing Lin [4] Mobile and Wireless Networks Uyless Black Prentice Hall Appendix A 2

3 Reference (2/2) [5] SS7 [6] Carrier Grade Voice over IP 2nd Daniel Collins Mc Graw-Hill Companies Inc 3

4 Outlines Introduction Signaling System Number 7 (SS7) Protocol Components and Links of SS7 PCS/PSTN Call Control Using ISUP Summary 4,, SS7,, PSTN PCS network SS7 PSTN (land-to-mobile), PCS MS (mobile-to-land),, signaling

5 Introduction 5, ( BB Call, GSM), ( PSTN,, PSDN, ADSL) PSTN, PSDN (circuit-switching, ie, dial-up) (packet-switching), -,, : CAS CCS SS7 CCS

6 Public Switched Telephone Network (PSTN) Three components: Customer premises equipment (CPE) Telephone set, private branch exchanges (PBX) The transmission facilities Trunks and subscriber lines The switching system Central offices (CO), tandems 6 PSTN,, circuitswitching ( ),, SS7, intelligent network, ISDN 3 : Customer premises equipment (CPE):,, (PBX) The transmission facilities:,, ( subscriber line) ( trunk) The switching system: Exchangers,,, Central office (CO), End office ( ) Tandem trunk Tandem CPEs : (charging zone for local call), (local tandem) CO Toll tandem ( ) inter-exchange tandem Co ( long distance calls)

7 PSTN Architecture Trunk (ex: E1) PBX Trunk CO Subscriber Line Tandem Trunk Basic Rate Interface ISDN Adaptor Trunk ISDN CO ISDN PBX Tandem Primary Rate Interface Trunk Trunk CO CO 7 ISDN: Integrated Services Digital Network ISDN,, BRI: basic rate interface provides 2B+D (B: 64Kbps voice, D: 16kbps signal) PRI: primary rate interface provides 23B+D (B:64Kbps voice, D: 64kbps signal)

8 Call Setup and Release A call requires a communications circuit between two subscribers The setup and release of connection is triggered by signals CO Trunk Tandem Trunk Tandem Trunk CO signal signal signal signal signal signal signal signal signal signal 8,,, circuit connection, (signal),,,, signal CC-AC-EC-LN, ex: , AC,, CO, router, (routing table), hop,, :,,,, : (interconnection), (information receiving), (control), (information transmitting), (altering), (busy testing), (attending) (supervision) central office, : (Battery Feed), (Over-voltage Protection), (Ringing), (Supervision), (Codec), (Hybrid) (Testing)

9 Signaling Systems Besides delivering subscriber voice and data information, telecommunication network requires a signaling system Tandems and COs perform all tasks for call controls Signaling is the communication of control information between the signaling elements via some prescribed protocol For control call setup, administration, disconnect of the circuit 9, call connection, release, Signaling system, signal Signal,,, tandem COs,, signaling elements,

10 Signaling on Subscriber Line Two types of signaling functions: Supervisory signals Supervising Alerting Call process Address signals Analog User-to- Network Signaling: DTMF (Dual Tone Multiple Frequency) * A 9 C # B D 10 Subscriber signaling voice,, DC signaling signal : Supervisory signals are used to initiate a call request, to hold or release an established connection Supervising : call connection, subscriber switching system subscriber lines trunk idle busy,,,,,, Alerting: subscriber, call, ring a called phone off-hook warning Call process :, subscriber,, (Reorder tone), (ring back tone) a busy tone ( ) Address signals contain, caller CAS Dial Pulse Dual Tone Multi-Frequency CCS message

11 Interoffice Trunk Signaling Control information exchange among the switches is achieved by interoffice trunk signaling Two approaches: Channel associated signaling (CAS) Signaling and voice share the same channel Common channel signaling (CCS) A separate signaling network to carry signaling message 11 user-to-network signaling, subscriber signaling ( CO tandems), (Interoffice trunk signaling, network-to-network signaling, inter-exchange signaling) Interoffice trunk signaling interoffice trunk signaling Signaling : CAS CCS CAS ( ): circuit-switched (signaling) (speech) Channel Associated Signaling (CAS) per-trunk, in-band signaling, the call control path speech, call control signal voice traffic R1 Multifrequency (MF) signaling, R2 Multi-frequency Compelled (MGC) signaling R1 Modified CCS ( ): signaling speech, outof-band signaling speech signaling CCS 1950s and 1960s

12 CAS Architecture 12 Advantage of CAS ( ): line signaling Disadvantages of CAS: signaling type, call setup and release database Signaling rate 30bps

13 CCS Architecture 13 CCS is a out-of-band signaling network,, CCS : CCS: Ex: R2 signaling, signaling system number 7 (SS7)

14 The Advantages of CCS Signaling can be efficiently delivered by using signaling links Since the all attempts are released by the signaling links, better utilization of voice trunks can be expected Singling can be performed during conversation 14 call control signal voice traffic, offices redundant links reliability connection, look ahead connection,,, local exchange carrier interchange carrier

15 Example of CCS Subscriber Line Off Hook Dial Tone On Hook CO CIC 1 CIC 50 Signaling Connection Voice Connection IAM(CIC=5, Called Number= ) ACM(CIC=5, ) ANM(CIC=5, ) REL(CIC=5, ) RLC(CIC=5, ) Conversation CO Ringing IAM: Initial Address Message ACM: Address Complete Message ANM: Answer Message REL: Release Message RCM: Release Complete Message CIC: Circuit Identification Code On Hook 15 ISUP, ISUP,, busy, IAM REL, caller RLC CIC: Circuit Identification Code physical link, TUP voice circuit

16 Signaling System Number 7 (SS7) Protocol 16 SS7, layer protocol

17 Signaling System No 7 The first CCS system is signaling system number 6 developed in the 1970s The modern CCS system is SS7 SS7 is a dedicated data communication network and similar to the packet network SS7 follows ISO 7 layer architecture SS7 is used for ISDN and PCS Signaling between a PCS network and the PSTN are typically achieved by the SS7 network , 1892 step-by-step switch, 1924 crossbar switch, 1960 stored program control switch, 1972 CCS, CCIS CCS No CCITT SS6, 1980 SS7, 1984, 1988 improvement SS6 2400bps data link signals SS7 64kbps data link signals SS7 plain old telephone service (POTS),, toll-free calling, number portability SS7 Intelligent Network (IN), SS7 signaling system satellite links SS7 CCITT ISDN

18 The SS7 Signaling Protocol OSI Layers OMAP The SS7 Layers MAP Application Presentation Session Transport TCAP ISDN-UP TUP SCCP Network MTP Level 3 Data Link MTP Level 2 Physical MTP Level 1 18 SS7 TCAP: Transaction Capability Application Part SCCP: Signaling Connection Control Part TUP: Telephone User Part ISUP: ISDN User Part INAP: Intelligent Network Application Part, TCAP MAP: Mobile Application Part OMAP: Operation Maintenance Administration Part MTP: Message Transfer Part NSP: Network Service Part SS7, OSI 7 layers

19 Message Transfer Part (1/2) MTP Level 1 Defines the physical, electrical and functional characteristics of the signaling MTP Level 2 Dealing with the transfer of messages on a given link from one node to another Provides reliable transfer of signaling messages between two directly connected signaling points MTP2 MTP3 ISUP 19 MTP (Message Transfer Part) SS7 protocol stack (layers) Open Systems Interconnection (OSI) seven-layer model Network Layer, Data Link Layer, Physical Layer MTP SS7 message source destination MTP level 1 signal link bearer 64kbps digital line T1 or E1 ( analog 4 or 3kHz spacing) 15 Mbps, 2 Mbps, ATM ITU-T Q702, Coding, Time slot number, bit rate, framing, impedance bit invert, MTP1 signaling terminal MTP level 2 MTP1,, error detection and correction ( ), flow control, signal unit delimitation and alignment ( ), initial alignment( ) MTP level 2 HDLC specification ITU-T Q703 (signaling link), : (delimitation, flag= , signal unit, SU), (alignment), (error detection, sequence number), (error correction), (initial alignment), (signaling link error rate monitoring), (flow control) MTP2 ( LSSU FISU MTP2 ), ( MSU) MTP3 LSSU (Link Status Signal Unit), FISU (Full-In Signal Unit), MSU (Message Signal Unit)

20 Message Transfer Part (2/2) MTP Level 3 Signaling message handling Providing message routing between signaling points in the SS7 network Signaling network management Rerouting traffic to other SS7 signaling links in the case of link failure, congestion or node failure Load-sharing 20 MTP level 3 signal (routing), STP (intermediate nodes), message MTP 3 network, network status information signal routing, ITU-T Q704 MTP3,, destination outgoing signaling link, ;,, ( SCCP) MTP3 signaling links load sharing signaling link,, link MTP3, SS7, MTP3, messages, (ex: congestion), available MTP-Transfer request, MTP-Transfer indication, MTP-Pause indication, MTP-Resume indication, MTP-Status indication

21 ISUP ISDN User Part Used as the protocol for setting up and tearing down phone calls between switches Circuit-related service To initiate a call between two switches To indicate that a call has been accepted by the called party To initiate call disconnection 21 MTP ISDN User Part (ISUP) Signaling Connection Part (SCCP) MTP TUP (Telephony User Part), TUP, ISUP, ISUP ISDN (Integrated Services Digital Network) application, ISUP call setup teardown, SS7 signaling protocol, OSI layer 4 layer 7 ISUP (ie, call control: voice,, ) (,, caller,, user to user signal), call status, trunk management ISUP Initial Address Message (IAM switches ) Answer Message (ANM Release Message (REL ) ISUP connection-oriented protocol ISUP, 2 POTS, 2 ISDN, 1 POTS 1 ISDN call control ISUP ( TCAP)

22 SCCP Signaling Connection Control Part Used as the transport layer for TCAP-based services Both connection-oriented and connectionless Mostly connectionless signaling Global title translation (GTT) capabilities The destination is determined from the global title 22 SCCP MTP, network layer, (ie, circuit-relative, ISUP end-to-end connection, ISUP MTP) (ie, noncircuit-relative, GTT efficient routing services) PCS cancellation con-circuit-related SCCP OSI 3,4 ( ), (message sequence), TCAP, timeout constraint SCCP connection-oriented ( connection,,, TCP) connectionless ( connection, UDP) connectionless ( Mobile system, user, connectionless) SCCP MTP, (point code), SCCP, (node between the originator and destination), global title addressing MIN, ( ), GTT, (point code)

23 TCAP TCAP (Transaction Capabilities Applications Part) Supporting the exchange of non-circuit related information between SS7 nodes Queries and responses sent between switches and databases are carried in TCAP messages Freephone (800/888), calling card, wireless roaming 23 TCP non-circuit-related Circuit-related signaling setup teardown central office trunk circuit Non-circuit-related service database (translations),, TCAP applications, transactions procedures, (operation) TCAP MAP, IS-41, SCP database 080,,,, TCAP, transaction, transaction Connectionless signaling only TCAP components syntax, Basic Encoding Rules (BER) standard ( OSI transfer syntax ) IS-41 mobility management, 50 TCAP operation (for inter-msc handoff, automatic roaming, OA&M) Intelligent network TCAP AP, hardware IS-41 TCAP SCCP class 0 connectionless service TCAP MAP, OMAP, INAP, etc

24 Application Layer Operations, Maintenance, and Administration Part (OMAP) Mobile Application Part (MAP) Application of TCAP IS-41 & GSM MAP are implemented in MAP layer INAP (Intelligent Network Application Part) 24 OMAP: network management TCAP, MAP TCAP, mobile IS-41 GSM MAP ISUP (ie, call control: voice,, ) (,, caller,, user to user signal), call status, trunk management parts : Broadband ISDN User Part: broadband ISDN connections setup/release( ISUP ) Telephone User Part: ( ISUP ) BSSAP INAP: Intelligent Network Application Part

25 Components and Links of SS7 25 SS7, SS7 voice trunk, SS7,, SS7, (ex: PSTN) SS7,, reliability, redundant fashion, signal, links traffic load share, 45%, link Error recovery SS7

26 SS7 Network SSP E-link STP B-link A-link A-link SSP SCP F-link SSP A-link STP STP Service Switching Point (SSP) Signal Transfer Point (STP) Service Control Point (SCP) D-link STP STP C-link Anther carrier s SS7 network 26 SSP: MSC, switch SCP: HLR/VRL STP: router D-link: STP pairs cross different vendors, ex: PSTN and PCS network B-link: two STP pairs in the same vendors

27 Signaling Point (SP) Each node in an SS7 network is an signal point (SP) Linkset Group of signaling links directly connecting two adjacent SPs For capability and security reasons SP SP SP SP signaling link linkset 27 SS7 (node computer), SP (signaling point) Signal point discrimination ( message address message, link SS7 ( ) (SP ), point code ( ), SS7 14 bit point code, signal SS7 MTU ANSI MTU, 24 bits point code,, ITU MTU, 14 bits point code China 24 bits point code SP adjacent, adjacent SP signaling link link 64 Kbps, 56 kbps, link, a linkset

28 Point Code Each SS7 network element is assigned with a unique point code The signaling address of the SP is known as a signaling point code (PC) STP STP point code =220 STP STP point code = SS7 ( ), point code ( ), SS7 14 bit point code, signal ITU-T

29 Basic Components SSP/Service Switching Point switching, service invocation STP/Service Transfer Point signal routing SCP/Service Control Point service logic execution IP/Intelligent Peripheral IP IP SSP SSP resources such as customized voice announcement, voice recognition, DTMF digit collection STP STP SCP SCP Voice STP STP 29 SSP SSP SS7 : SSP (Service Switching Point),, subscriber trunk, billing voice signaling PSTN, SSP, tandem end office PCS, SSP MSC SSP CPE subscriber lines, CPE call processing, SSP,, SSP SS7 source destination signaling STP (Service Transfer Point) (routing) STP SSP STP ( ):, voice, STP SS7, SS7 signal, routing reliability, STP STP, screening SS7 OSI layer 3 STP SSP SCP software & database 0800 SSP SCP, SCP address SSP, SSP mobile applications, SCP HLR or VLR SCP SSP, SSP SCP ( STP pair, for reliability), components vendor s equipment IP (Intelligent Peripheral), voice response units, voice announcers, DTMF sensors for caller activated services

30 Service Switching Point (SSP) Trunks connects SSPs to carry user data/voice information Signaling links connect SCPs to STPs, and STPs to SSPs SCP SCP IP IP STP STP STP STP SSP SSP SSP SSP Voice 30 SSP local access ISDN interface Call setup teardown SS7 protocols

31 Signal Transfer Point (STP) To transfer messages from one SP to another SCP SCP IP IP STP STP STP STP SSP SSP SSP SSP Voice 31 STP router, packet switching, messages MSU: message signal unit STP MSU, routing table SPC2, link SPC 2 MSU, context

32 Service Control Point (SCP) A network entity contains additional logic and can be used to offer advanced services The switch sends a message to the SCP asking for instructions The SCP tells the switch which actions need to be taken An good example toll-free 080 number 32 SCP database software, VLR, HLR SCP SCP, switch, switch SSP (Service Switching Point) SSP SCP, SCP, SSP SSP, 080, SSP SSP SCP, TCAP SCP SCP,, 080, SCP SSP routable number SSP SCP TCAP SCCP connectionless SSP, SCP end office, end office IP, IP End office IP ISND

33 Subsystem Number Subsystem numbers (SSNs) are the addresses of applications Each database has its SSN SSN used in mobile network Application SSN Reserved HLR VLR MSC EIR AuC application signal point application, communication interface to application, ASE (Application service entity signaling point application, ASE TCAP ASE, MAP OMAP subsystem number transaction, entity HLR, SSN SSN application SCP, ie, SCP point code

34 SS7 Signaling ISUP Messages The Telephone Network INAP/TCAP Messages Service + Control Point Service Data Point Signal Transfer Point Control Layer Intelligent Peripheral Transport Layer Class 4 Tandem Switch Class 5 End Office Switch Circuit Switched Network 34 (Voice) (CO Switches) Trunk Signaling) SS7 (Call Control) SS7 ISUP SS7 (Signal Transfer Point STP) (Originating Switch) (Terminating Switch) (IN Services) SS7 TCAP SS7 (Service Control Point SCP) (Announcement) (Interactive Voice Response IVR) SCP (Intelligent Peripheral IP) DTMF SCP Class 4 Local exchange, class 5 (ex: RGW)

35 Types of Signaling Links in SS7 Another carrier s SS7 network One SS7 network SCP A-links A-link: Access link B-link: Bridge link C-link: Cross link D-link: Diagonal link E-link: Extended link F-link: Full associated link STP D-link STP B-link STP C-link A-links A-links A-links E-links SSP F-link SSP SSP SSP SSP 35 SS7 64kbps, full duplex, digital transmission channel 3 components of SS7 are STP, SCP, SSP A-link: STP-SCP, STP-SSP( MSC,SMSC) SSP or SCP signaling link, Access Link (Alink), STP pair MSC SSP, A-link MSC PSTN STP pair, A-link 56kbps, 64kbps T1 E1 The number of A-links between an SSP and an STP pair can be up to 128 Most switch suppliers have limited 16 E-link: reliability, STP SSP,, E-link B-link: STP pairs STP-STP C-link: STP pair 2 STP, C-link status message D-link: Diagonal link, vendor STP-STP pair (ex: PSTN and PCN), signals link D-links are deployed in a quad arrangement with three-way path diversity The maximum link set size is 64 Signaling links that connect STPs of different networks (eg, PCN and PSTN) are called D-link

36 Interconnection between Two SS7 network Signaling Links SCP STP STP STP STP SCP HLR SCP: Service Control Point STP: Signal Transfer Point SSP: Service Switching Point SSP Trunk MSC PCS Network PSTN 36 SS7 PCS PSTN, PCS network PSTN (signal) (trunk) STP STP ( router), D-link signaling links PSTN SSP PCS MSC PSTN user data SSP Tandem, Tandem MSC Type 2A PSTN user data SSP End office, End office MSC, Type 2B, 080, tandem, Type 2B interface, PSTN STP MSC, STP,, PSTN STP PCS MSC, A-links

37 SS7 Messages (bits) B Flag BSN I LI Square CRC FSN F I B B First bit transmitted (a) Fill-in Signal Unit (FISU) or (bits) B Flag BSN I LI Square Status CRC FSN F I B B First bit transmitted (b) Link Status Signal Unit (LSSU) n (2 n 272) 16 (bits) B Flag BSN I LI Square SIO SIF CRC FSN F I B B First bit transmitted (c) Message Signal Unit (MSU) 37 SS7 : MTP 2 (Fill-In Signal Unit) FISU (Link Status Signal Unit) LSSU MTP 3, Message Signal Unit (MSU) Flag= (delimitation) FSN: Forward Sequence Number, BSN: Backward Sequence Number, message flow Retransmission: SS7 Forward (Backward), BIB=1 (FIB=1), FSN (BSN) LI SS7 MTU, LSSU, FISU : Message signal unit (MTU): LI>5, MTP2 MTP3, LI: Length Indicator, Level 3 upper layer Link status signal unit (LSSU): MTP2, upper layer level 3, LI 8-16 bits Status ( LI=1 or 2) Fill-in signal unit (FISU): MTP2, upper layer level 3 (LI=0) LI 2 bits SIO (Service Information Octet) Service indicator, upper-level protocol SCCP ISUP SIP Subservice field, signaling numbering plan (ie, point code ) SSF (4 bits): Sub-service Field, ( =00xx

38 Message Signal Unit (MSU) variable length (bits) DPC DPC DPC OPC OPC OPC Member Cluster NetworkMember Cluster Network SIO SLS Message content First bit transmitted (a) ANSI MSU variable length (bits) SIO DPC OPC SLS Message content 4 4 SI SFF (a) ITU MSU First bit transmitted DPC = Destination Point Code OPC = Origination Point Code SIO = Service Information Octet SI = Service Indicator SFF = Subservice Field SLS = Signaling Link Selection International Signaling gateways SP National Signaling plane 2 International Signaling plane SP SP 38 National Signaling plane 1 SS7 MTU DPC = Destination Point Code, OPC = Origination Point Code source SLS = Signaling Link Selection message, link ANSI (American National Standards Institute) MTU, 24 bits point code,, ITU-T (International Telecommunication Union Telecommunications Standardization Sector) MTU, 14 bits point code China 24 bits point code, 6 ( 3 bit ), 8 bit /, 3 bit /, 14 bits , , ANSI SLS 8 bits, 3 bits ITU SLS 4 bits ANSI point code hierarchical, network-cluster-member, 8 bits operator network, 16 bits point code, point codes Question: SS7 MSU,? Answer: signaling gateway (SGs) international SG ANSI point code, ITU point code

39 SS7 Message Signal Unit (ISUP) MTP Level 2 ISUP User Data Upper MTP Layer Level 3 Level (Flag) (bit) CK upper RL SIO / LI FSN BSN CIC OPC DPC Example: ITU-T ISUP message F I B B I B First bit transmitted 4 4 SSF SI BSN: Backward Sequence Number BIB: Backward Indicator Bit FSN: Forward Sequence Number FIB: Forward Indicator Bit LI: Length Indicator SIO: Service Indicator Octet SI: Service Indicator SSF: Sub-service Field RL: Routing Label DPC: Destination Point Code OPC: Originating Point Code CIC: Circuit Identification Code SIF: Signaling Information Field 39 Switch A Switch B signaling Question: Switch A Switch B, SS7? Question: ISUP Switch A Switch B path? Answer: ISUP CIC (Circuit Identification Code), message switch (DPC, OPC) circuit SSP ISUP SSP CIC Circuit Identification Code voice circuit SSP trunk DPC + OPC + CIC CIC, CIC called switch calling switch ( trunk) ITU-T ISUP CIC 4 bit spare, message type, Message type, Ex: IAM, COT ANSI CIC 14 bits, spare 2 bits, Message type 8 bits DUP Bearer identification code, data circuit

40 MTP Layer Routing Destination Point Code (DPC) = actual address of the destination node Lookup tables is used in the MTP Routing Table DPC Link Set ,12 : : CIC OPC DPC SSP DPC Link Set ,32 : : STP Speech circuit 13 STP STP STP 61 DPC Link Set : : SSP 300 signal voice 40 SS7, MTP SCCP : SSP, STP, or SCP MTP 1-3,, DPC DPC MTP OPC originating OPC, DPC SLS (signaling link selection) MTP 3 field OPC DPC, source IP destination IP CIC voice MTP, SCCP SCCP address called party address (PC+SSN+GT) calling party address SCCP GTT routing

41 ISUP Routing MTP3 provides node-to-node delivery Signal point can get the output signaling link by looking MTP 3 routing table ISUP provides end-to-end delivery By using the called party number, ISUP provides destination point code to MTP3 SSP can get the next hop (SSP) by looking ISUP trunk routing table 41 MTP signal point routing table SP destination point code signaling link SSP MTP3 STP ISUP, OPC/DPC SSP point code ISUP, SSP trunk routing table called party number hop SSP DPC ISUP CIC for trunk, SSP SCCP routing information MTP3

42 SS7 Message Signal Unit (SCCP) MTP Level 2 SCCP User Data Upper MTP Layer Level 3 Level (Flag) (bit) CK upper RL SIO / LI FSN BSN SLS OPC DPC Example: ITU-T SCCP message F I B B I B First bit transmitted 4 4 SSF SI BSN: Backward Sequence Number BIB: Backward Indicator Bit FSN: Forward Sequence Number FIB: Forward Indicator Bit LI: Length Indicator SIO: Service Indicator Octet SI: Service Indicator SSF: Sub-service Field RL: Routing Label DPC: Destination Point Code OPC: Originating Point Code SLS: Signaling Link Selection SIF: Signaling Information Field 42 SS7 signal unit, MTP signal (upper layer ), LI : Fill-in signal unit (FISU): MTP2, upper layer level 3 (LI=0) Link status signal unit (LSSU): MTP2, upper layer level 3, LI 8-16 bits SF ( LI=1 or 2) Message signal unit (MTU): LI>5, MTP2 MTP3 LI: Length Indicator, MSU, Level 3 upper layer LI 2 bits ( / ) SS7, FISU LSSI, MTU, RL (Routing Level), DPC, Flag= (delimitation) FSN: Forward Sequence Number, BSN: Backward Sequence Number, message flow Retransmission: SS7 Forward (Backward), BIB=1 (FIB=1) FSN (BSN) SSF: Sub-service Field, ( =00xx =10xx), SI: Service Indicator,

43 SCCP Message Embedded TCAP Message Level 2 First bit transmitted Level 3 Level 2 8 (Flag) 16 SCCP (Flag) bit F B CK SIF RL SIO / LI FSN BSN I B I B SCCP message SLS OPC DPC 4 4 SSF SI=0011 User Data Calling PartyCalled Party Address Address TCAP message Component Portion Transaction Portion Protocol Class Message Type Message Type: Unitdata Protocol Class: Class 0 or Class 1 43 SCCP message TCAP message SSF: Sub-service Field, ( =00xx =10xx), SI: Service Indicator, (MTP3=0,1/TUP=4/ISUP=5/SCCP=3) SIF: Signaling Information Field, bytes CK: check bits

44 SCCP Layer Routing Parameters in the SCCP Called Party Address (PC+SSN+GT) Calling Party Address (PC+SSN+GT) At least GT or Point Code (PC) +SSN Global Title (GT) is the dial digits usually For example, 0800 or mobile phone number SCCP provides routing information to MTP If SCCP has PC of called party, then SCCP sends it to MTP3 If SCCP only has GT, SCCP translates GT to PC+SSN 44 SCCP calling party address called party address, routing information MTP MTP link calling party address/ called party address PC, SSN, GT, GT PC+SSN SCCP called party address point code MTP RL point code SCCP called party address global title subsystem number MTP MTP SCCP

45 Global Title Translation Global Title Translation (GTT) is a function defined within SCCP GTT is the process of translating global title to find the destination SSP 0800 calls in SSP Perform GTT at a STP and get the PC+SSN of application SCP returns the real telephone number to STP STP tells SSP the final destination Call setup 45 GTT: Global Title Translation SCCP function GTT HLR/VLR SS7, hop point code point code 800, : MSC (SSP) 800, request message GTT STP STP 800 translation services, SCP HLR/VLR (SSN), request SCP SCP 800 xxx xxxx, directory number SCP STP (STP GTT message SCP hop point code) STP MSC (SSP) STP, MTP1-3, SCCP GTT Ex: mobile phone, HLR trunk connection GMSC, GMSC GT HLR, TCAP query, trunk connection form GMSC MSC of mobile

46 GTT in GSM For intra-gsm network message delivery The destination address of the message may be a simple destination point code (DPC) that can be used by the MTP for direct routing For inter-gsm network message delivery The SCCP translates the actual destination address by Global Title Translation (GTT) and sends to the originating node GTT and Inverse GTT in Gateway MSC Security Issue 46 PLMN (intra-gsm), entity, MTP3 entity DPC, PLMN, SCCP GTT,, GTT STP, STP GTT,, GTT HLR, HLR, VLR HLR database application, addressing SSN node SSN, global title global title message SSN point code

47 GTT Example DPC * A VLR STP A GTT Table (A) GT DPC * GA : : DPC * GA SCP A SS7 Network A GA International SS7 Network DPC * GB STP C *: Global Title of HLR DPC * GB GTT Table (GB) GTT Table (GA) GT DPC GT DPC * GA * GB : : : : DPC * B GB STP B SS7 Network B DPC *SCP B HLR SCP B GTT Table (B) GT DPC * GA : : 47 VLR, VLR HLR ( mobile telephone number PLMN, SSN=HLR), : VLR/SCP request message GTT STP A STP A, SCCP address GTT Table, hop (GA) point code, DPC, request, international SS7 network, gateway SSP SSP GA, address GTT Table, hop (GB) point code, DPC, request STP C ( STP C GPP), SSP GB, address GTT Table, hop (STP B) point code, DPC, request STP B, address GTT Table, hop (SCP B) point code, DPC, request SCP B SSN HLR GTT (for SCP B), GTT

48 Basic Call Control Using ISUP 48 SS7 ISUP layer ISUP

49 ISUP Message ISUP messages Establishes circuit-switched network connections Call setup/release between the PSTN and a PCS network ISUP messages that are delivered by MTP routing 49 PCS network PSTN SS7 ISUP ISUP call control, PCS PSTN, ISUP ISUP MTP, MTP ISUP Type 2A with SS7 (tandem MSC), PSTN (land-to-mobile), PCS (mobile-to-land),,,

50 Basic Call Setup Phone A Off Hook Dial Tone Switch 1 Switch 2 Phone B Dial Digits (Setup) Dial Tone Off (Preceeding) IAM (Setup) (Setup) Paging Initial Dial Tone (Page Response) ACM (Alert) RAB Assignment Call Path Establishment Ringback Tone (Alert) ANM (Connect) Ringback Tone Off (Connect) Ringback Tone Off (Connect Ack) Ring Tone (Alert) Off Hook (Connect) Connect Ack Conversation 50 Phone A Phone B switch Off Hook: Dial Tone: Dial Digits: Ring Tone: Ringback Tone: ring switch ISUP message, Initial Address Message (IAM): trunk Address Complete (ACM):, alert, trunk, ie voice circuit Answer Message (ANM): Phone B, Phone switch signal switch 1 telephone end office end office switch 1 dial tone End office DTMF Dual-Tone Multi-Frequency switch 1 end office end office 20Hz 80V AC trigger altering ringback tone originator caller Phone B busy tone Phone B ringback tone

51 Basic Call Release Phone A Switch 1 Switch 2 Phone B Conversation On Hook (Disconnect) Release REL RLC Call Path Release Disconnect Release Call Path Release 51 Phone A, Phone B On Hook: switch ISUP message: Release (REL): Release Compete (RLC): trunk idle switch Release Compete (RLC) 05 1, trunk

52 ISUP Messages (1/2) IAM (Initial Address Message) called number, calling number, transmission requirement, type of caller, other information ACM (Address Complete Message) One-way path from destination to calling switch Note: Called switch generates the ring-back tone CPG (Call Progress) Provide additional information to calling switch ANM (Answer Message) 52 call setup messages: Initial Address Message (IAM): trunk called number, calling number, transmission requirement ( 64kbps), type of caller ( ordinary, operator, payphone), other information (ex: satellite, ) Address Complete (ACM): (one-way, from destination to originating switch), ring-back tone ( destination switch ), trunk ACM optional, ACM, caller ring back tone toll-free numbers, called party IVR ACM Backward Call Indicators ( originating exchange), the status parameter available called party available, the status parameter no indication ( ), the charge field no indication ( ), calling party busy tone Call Progress (CPG): calling switch, CPG optional Answer Message (ANM): called party, Called party message :

53 ISUP Messages (2/2) REL (Release) Message To release the call RLC (Release Complete) Message Complete the call 53 call release messages: Release (REL): Release Compete (RLC): trunk idle, ISUP, COT (Continuity), SUS (Suspend) COT (Continuity) (forward circuit ) continuity test continuity test, criteria set SUS (Suspend) caller, subscriber line SUS tandem, ( CO, SUS ) SUS, REL, RLC ISDN party, REL ISND party, SUS, REL, RLC

54 PCS Network and PSTN Call Control Using ISUP 54 PSTN (land-to-mobile), PCS (mobile-to-land),, signaling

55 Interactions between a PCS Network and the PSTN Interconnection Interfaces Message Routing Mobility Management Call Control 55 (interconnection), PCS PSTN (interaction) 4 : 1 (Interconnection Interfaces):, PCS network PSTN 2 (Message Routing): PCS network PSTN, 3 (Mobility Management): mobile users 4 (Call Control): mobile user call control

56 Land-to-Mobile Call Setup and Release PSTN PCS Network STP STP 4 STP STP End Office Tandem MSC Step 1 Step 2 IAM COT IAM COT ACM ANM ACM ANM Step 3 Step 4 Conversation using trunks (6) and (7) Step 5 REL RLC REL RLC Step 6 56 tandem Type 2A with SS7 (Tandem MSC) Land-to-Mobile Call Setup and Release, signaling (1) -> (2) -> (3) -> (4) -> (5), trunk,, signaling Step 0 PSTN (MIN), EO (end office) EO HLR, EO HLR, temporary local directory number (TLDN) EO HLR, EO MIN (ie, GMSC) Step 1 EO TLDN, Initial Address Message (IAM) PCS s MSC,, trunk EO busy, IAM tandem IAM continuity check ( (1)->(2)->(3)->(4)->(5)) Step 2 EO tandem IAM continuity check, trunk, continuity check, EO Continuity Message (COT) tandem, trunk Step 3 MSC IAM, MSC MS : Event 1 MS, call forwarding call waiting, MSC Release (REL) EO, busy line situation Event 2 MS idle, MSC Address Complete (ACM) EO ( (5)->(4)->(3)- >(2)->(1)) Event 3 MS ( ), MSC REL EO Step 4 MS, MSC Answer Message (ANM) EO, Steps 5 and 6 PSTN (calling party ), EO Release (REL), MSC REL, Release Compete (RLC), trunk idle EO tandem Release Compete (RLC) 05 1, trunk

57 Mobile-To-Land Call Setup and Release PSTN Local Exchange Carrier LEC2 Interexchange Carrier Local Exchange Carrier LEC1 PCS Network STP STP STP STP STP STP End Office Tandem 2 Switch Switch Tandem 1 MSC IAM COT IAM COT IAM COT IAM COT IAM EXM COT ACM ANM ACM ANM ACM ANM ACM ANM ACM ANM Conversastion SUS REL RLC SUS REL RLC SUS REL RLC SUS REL RLC SUS REL RLC 57 tandem Type 2A with SS7 (Tandem MSC) Mobile-to-Land Call Setup and Release, PCS network Local Exchange Carrier, LEC1 Interexchange Carrier, IXC LEC2 Land-to-Mobile, MSC Tandem 1, Exit Message (EXM) MSC, SS7 (IAM) IXC Tandem 1 IXC ACM, ANM, REL, EXM timer timeout ( Tandem 1 IAM IXC timer), Tandem 1 EXM MSC Continuity (COT), Tandem 1 EXM MSC, PSTN (called party), End office Suspend Message (SUS) EO SUS timer, EO : Event 1 MS (calling party), MSC REL EO trunk Event 2 PSTN, EO Resume Message (RES) MSC, SUS timer Event 3 SUS timer, EO trunk REL MSC, MSC SUS, SUS timer, MSC : Event 1 ( Event 1) MS (calling party), The MSC REL EO trunk Event 2 ( Event 2) MSC EO RES, MSC SUS timer Event 3 ( Event 3) MSC EO REL, MSC FLC Event 4 SUS timer, MSC

58 Summary SS7: out-of-band signaling method Components and Links of SS7 3 components: STP, SSP and SCP 6 links: A-F links Interconnection between PCS network and PSTN PCS/PSTN Call Control Using ISUP Land-to-Mobile Call Setup/Release Procedures Mobile-to-Land Call Setup/Release Procedures 58