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CNS 479R Voice Over IP

CNS 479R Voice Over IP. Signaling System 7 Gary D. Brown, Guest Lecturer Lecture 2. Signaling System 7 (SS7). Introduction SS7 Network Architecture SS7 Protocols SS7 Call Signaling VoIP Issues. SS7 Protocols. Architecture Definitions Functional Divisions TDM-based Transport Protocols

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CNS 479R Voice Over IP

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  1. CNS 479R Voice Over IP Signaling System 7 Gary D. Brown, Guest Lecturer Lecture 2 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  2. Signaling System 7 (SS7) • Introduction • SS7 Network Architecture • SS7 Protocols • SS7 Call Signaling • VoIP Issues UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  3. SS7 Protocols • Architecture • Definitions • Functional Divisions • TDM-based Transport Protocols • IP-based Transport Protocols • Application-layer Protocols • Call Control • Messages • Message Flows UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  4. SS7 Protocols—Architecture UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  5. SS7 Protocols—Definitions • MTP1 Message Transfer Part Layer 1 • MTP2 Message Transfer Part Layer 2 • MTP3 Message Transfer Part Layer 3 • SCTP Stream Control Transmission Protocol (IP) • M3UA MTP3 User Adaptation Layer (IP) • SCCP Signaling Connection Control Part • TCAP Transaction Capabilities Application Part • ISUP ISDN User Part • TUP Telephone User Part (not shown—obsolete) UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  6. SS7 Protocols—Functional Divisions • TDM-based Transport (traditional) • MTP1 • MTP2 • MTP3 • IP-based Transport • Ethernet (IP network) • SCTP • M3UA • Application Protocols • SCCP/TCAP • ISUP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  7. SS7 Protocols—TDM-based Transport • MTP1 Message Transfer Part Layer 1 • Physical layer • DS0 in T1 or E1 (A-link, F-link) • V.35 modem • Satellite link • 64 Kbps bandwidth • 56 Kbps in “robbed-bit” T1 infrastructure • ITU-T Q.702 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  8. SS7 Protocols—TDM-based Transport • MTP2 Message Transfer Part Layer 2 • Data Link Control layer • Error Detection and Correction (CRC-16) • Packet Sequencing • Link Status Indicators • Signal Units • FISU (Fill-in Signal Unit)—permits immediate detection of link error • LSSU (Link Status Signal Unit)—provides link status between two SS7 nodes • MSU (Message Signal Unit)—carries higher level protocol messages • ITU-T Q.703 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  9. SS7 Protocols—TDM-based Transport • MTP3 Message Transfer Part Layer 3 • Network layer • Routes SS7 messages to their destination nodes • Reroutes SS7 messages during network failures • Network Status • Signaling Link availability • Point Code (Node) availability • Congestion Control • Levels 0 (None), 1 (Some) and 2 (Severe) • Initiates local congestion control on SS7 message reception (“surge”) • Responds to remote congestion control indication by throttling transmission • Link Set Changeover and Changeback • ITU-T Q.704 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  10. SS7 Protocols—Functional Divisions • TDM-based Transport (traditional) • MTP1 • MTP2 • MTP3 • IP-based Transport • Ethernet (IP network) • SCTP • M3UA • Application Protocols • SCCP/TCAP • ISUP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  11. SS7 Protocols—IP-based Transport • SCTP Stream Control Transmission Protocol • Reliable Transport • Datagram and/or Stream • Redundancy • Multiple Data Streams • Multi-homing (multiple IP addresses) • Active/Standby • Efficiency • No “Head of Queue” Blocking • Short timeouts • Heartbeats • IETF RFCs 2960, 3286, 3309 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  12. SS7 Protocols—IP-based Transport • M3UA MTP3 User Adaptation Protocol • Adaptation of SS7 Layer 4 protocols/MTP3 interface to IP network transport • Appears as MTP3 interface to Layer 4 protocols • Appears as IP-based application to SCTP • Maps between • SS7 Point Codes (OPC/DPC) and IP addresses • SS7 Point Codes with Circuit Identification Codes (OPC/DPC/CIC) and IP addresses (optional) • IETF RFC 4666 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  13. SS7 Protocols—Functional Divisions • TDM-based Transport (traditional) • MTP1 • MTP2 • MTP3 • IP-based Transport • Ethernet (IP network) • SCTP • M3UA • Application Protocols • SCCP/TCAP • ISUP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  14. SS7 Protocols—Application Protocols • SCCP Signaling Connection Control Part • Transport interface between TCAP and MTP3 • Supports connectionless, “non-circuit” based messages • Traffic Management • Maintains Signaling Point Status • Availability of Point Codes (SS7 Nodes) • Maintains Subsystem Status • SCCP “user” availability (specific applications) • Reroutes messages around failed subsystems (redundancy) • ITU-T Q.711-Q.716 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  15. SS7 Protocols—Application Protocols • TCAP Transaction Capabilities Application Part • Non-circuit related transactions • Common interface for transaction-type applications • Global Title Translation (800, 900 Numbers) • Line Information Database (LIDB) Query • Wire-line/wireless Local Number Portability Query • Directory Assistance Query • Protocol interface for application-oriented protocols • INAP (Intelligent Network Application Protocol) • IS-41 (North American wireless call control protocol) • MAP (Mobile Application Protocol—ITU) • ITU-T Q.771-Q.775 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  16. SS7 Protocols—Application Protocols • ISUP ISDN User Part • Call Control Signaling (call setup and teardown) • National Variants • ITU 88 (14-bit PC/12-bit CIC) ANSI 88 (24-bit PC/14-bit CIC) • ITU 92 (14-bit PC/12-bit CIC) ANSI 92 (24-bit PC/14-bit CIC) • ITU 96 (14-bit PC/12-bit CIC) ANSI 96 (24-bit PC/14-bit CIC) • ETSI (14-bit PC/12-bit CIC) ANSI 2000 (24-bit PC/14-bit CIC) • BT ISUP (14-bit PC/12-bit CIC) (United Kingdom and former colonies) • China (24-bit PC/14-bit CIC)(ANSI MTP3/ITU ISUP) • Telefónica (14-bit PC/12-bit CIC) (Spain, Portugal, South America) • ITU-T Q.761-Q.769 UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  17. SS7 Protocols—Call Control • ISUP Messages • ISUP Call Control Message Flows • Call Setup • Call Teardown UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  18. SS7 Protocols—ISUP Messages • Call Control Messages (most commonly used) • ACM Address Complete Message • ANM Answer Message • CCR Continuity Check Request • CFN Confusion • CON Connect • COT Continuity Message • CPG Call Progress Message • CRG Charge Information Message • IAM Initial Address Message • INF Information Message • INR Information Request Message • REL Release Message • RES Resume Message • RLC Release Complete Message • SAM Subsequent Address Message • SUS Suspend Message • USR User-to-User Information UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  19. SS7 Protocols—ISUP Messages • Circuit Management (most commonly used) • BLA Blocking Acknowledgement • BLO Blocking • CGB Circuit Group Blocking • CGBA Circuit Group Blocking Acknowledgement • CGU Circuit Group Unblocking • CGUA Circuit Group Unblocking Acknowledgement • CQM Circuit Group Query • CQR Circuit Group Query Response • GRS Circuit Group Reset • GRA Circuit Group Reset Acknowledgement • FAA Facility Accepted • FAC Facility • FAR Facility Request • FOT Forward Transfer • FRJ Facility Reject • IDR Identification Request • IRS Identification Response • RSC Reset Circuit • UBL Unblocking • UBA Unblocking Acknowledgement • UCIC Unequipped Circuit Identification Code UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  20. SS7 Protocols—ISUP Messages • Message “Direction” Concept • Forward Direction • Messages passed in the direction from the calling party to the called party • Sometimes referred to as “downstream” • Backward Direction • Messages passed in the direction from the called party to the calling party • Sometimes referred to as “upstream” UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  21. SS7 Protocols—ISUP Messages • Common ISUP Header • All ISUP message have common message header • Originating Point Code (OPC) • Point code of switch transmitting original message • Destination Point Code (DPC) • Point code of switch intended to receive message • Circuit Identification Code (CIC) • Identifies circuit between transmitting switch and receiving switch; not necessarily the original and intended switches! UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  22. SS7 Protocols—ISUP Messages • IAM Initial Address Message • Forward message indicating seizure of an outbound circuit and to transmit number and other information • SAM Subsequent Address Message • Forward message indicating additional called party number information (ITU only) • COT Continuity Message • Forward message indicating circuit continuity test is successful • ACM Address Complete Message • Backward message indicating all address signals required for routing call to called party have been received UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  23. SS7 Protocols—ISUP Messages • CPG Call Progress Message • Backward message indicating significant event has occurred • ANM Answer Message • Backward message indicating the called party has answered • REL Release Message • Forward or backward message indicating the circuit is being released due to some reason • RLC Release Complete Message • Forward or backward message, sent in response to a Release message, indicating the circuit has been put into an “idle” condition UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  24. SS7 Protocols—ISUP Messages • SUS Suspend Message • Message indicating subscriber has disconnected and the call has been suspended • RES Resume Message • Message indicating subscriber has reconnected and the call has been resumed • RSC Reset Circuit Message • Message forces circuit into “idle” state; causes any call or circuit seizure to be terminated • CFN Confusion Message • Message indicates confusion about message just received; usually happens during congestion or because of software bug UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  25. SS7 Protocols—Call Control • ISUP Messages • ISUP Call Control Message Flows • Call Setup • Call Teardown UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  26. SS7 Protocols—Call Setup Message Flow UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  27. SS7 Protocols—IAM Message Flow Calling CO switch sends Initial Address Message(IAM) in forward direction to called CO switch via tandem switches, and each switch seizes an outbound circuit and connects the backward talk path. CO Switch Tandem Switch Tandem Switch CO Switch IAM IAM IAM IAM IAM IAM IAM STP STP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  28. SS7 Protocols—ACM Message Flow Called CO switch alerts called party (ring), sends Address Complete Message(ACM) in backward direction to calling CO switch via tandem switches, and calling CO switch plays ringing. CO Switch Tandem Switch Tandem Switch CO Switch ACM ACM ACM ACM ACM ACM ACM STP STP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  29. SS7 Protocols—ANM Message Flow Called party answers, called CO switch sends Answer Message(ACM) in backward direction to calling CO switch via tandem switches, and all switches connect forward talk paths. CO Switch Tandem Switch Tandem Switch CO Switch ANM ANM ANM ANM ANM ANM ANM STP STP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  30. SS7 Protocols—Call Teardown Message Flow UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

  31. SS7 Protocols—REL Message Flow Caller hangs up, calling CO switch sends Release Message(REL) in forward direction to called CO switch via tandem switches, and each switch sends Release Complete Message (RLC) inbackward direction, disconnects the talk path and idles the circuit. CO Switch Tandem Switch Tandem Switch CO Switch RLC RLC RLC REL REL REL REL RLC REL REL RLC RLC REL RLC STP STP UVSC CS 479R – Telecommunications and Voice Over IP Signaling System 7 Protocols

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