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A ISUP Messages Switch Lab IP Telephony Gateways Gonzalo Camarillo Royal Institute of Technology Master’s Thesis in Teleinformatics Supervisors: Elin Wedlund Zsolt Haraszti SwitchLab SwitchLab Ericsson Telecom AB Ericsson Telecom AB Ulf Bilting Department of Teleinformatics Royal Institute of Technology Examiner: Fredrik Orava Department of Teleinformatics Royal Institute of Technology Stockholm 1998-11-02 Acknowledgement I would like to thank Henning Schulzrinne, professor at Columbia University and father of SIP, for his direction and all his advice on the implementation of the gateway prototype. i IP Telephony Gateways ii Abstract Abstract There are two different approaches to provide telephone services at present: to use the tra- ditional switched network and to use the Internet. Both approaches employ different ways to establish connections, transmit the voice and terminate calls. This study focuses on the establishment of connections and the release of them. Different protocols are analysed and finally SIP and SS7 are described. The possible compatibility between them and the mapping between both message formats are also analysed. Features of both networks are described, and the functions of a gateway between them are outlined. iii IP Telephony Gateways iv Table of Contents Table of Contents 1 Introduction....................................................................................................... 1 2 Traditional Circuit-Switched Telephony .......................................................... 3 2.1 ISDN and PSTN........................................................................................... 4 2.2 SS7 ............................................................................................................... 5 2.2.1 MTP............................................................................................. 6 2.2.2 SCCP........................................................................................... 8 2.2.3 TCAP........................................................................................... 9 2.2.4 TUP ............................................................................................. 9 2.3 ISUP ............................................................................................................. 9 2.3.1 Example of signalling operation ................................................. 11 3 IP Telephony..................................................................................................... 13 3.1 Underlying architecture................................................................................ 13 3.1.1 IP ................................................................................................. 15 3.1.2 UDP............................................................................................. 16 3.1.3 TCP ............................................................................................. 17 3.2 RTP .............................................................................................................. 17 3.3 SIP................................................................................................................ 18 3.4 H.323............................................................................................................ 21 3.5 SIP vs H.323................................................................................................. 21 4 Mapping between ISUP and SIP....................................................................... 23 4.1 SIP to ISUP State Machine .......................................................................... 26 4.2 ISUP to SIP State Machine .......................................................................... 26 4.3 Voice Path .................................................................................................... 26 4.4 Gateway architecture.................................................................................... 27 4.5 Network architecture.................................................................................... 28 4.5.1 SIP temination............................................................................. 28 4.5.2 SIP bridging ................................................................................ 29 4.5.3 SIP bridging without media gateway .......................................... 30 4.5.4 Tunnelling approach.................................................................... 30 4.6 Mapping of parameters ................................................................................ 30 5 Conclusions....................................................................................................... 33 6 References......................................................................................................... 35 6.1 Traditional Circuit-Switched Telephony...................................................... 35 6.2 IP Telephony ................................................................................................ 35 6.3 Implementation ............................................................................................ 36 v IP Telephony Gateways Appendices A ISUP messages.................................................................................................. 37 A.1 Signalling messages sent just in the forward direction ................................ 37 A.1.1 COT: Continuity message ........................................................... 37 A.1.2 FOT: Forward transfer message.................................................. 37 A.1.3 IAM: Initial address message...................................................... 37 A.1.4 SAM: Subsequent address message ............................................ 38 A.2 Signalling messages sent just in the backward direction ............................. 38 A.2.1 ACM: Address complete message .............................................. 38 A.2.2 ANM: Answer message .............................................................. 39 A.2.3 CPG: Call progress message ....................................................... 39 A.2.4 CON: Connect message .............................................................. 40 A.3 Signalling messages sent in either direction ................................................ 40 A.3.1 BLO: Blocking message ............................................................. 40 A.3.2 BLA: Blocking ACK message .................................................... 41 A.3.3 CGB: Circuit group blocking message ....................................... 41 A.3.4 CGBA: Circuit group blocking ACK message ........................... 41 A.3.5 GRS: Circuit group reset message .............................................. 42 A.3.6 GRA: Circuit group reset ACK................................................... 42 A.3.7 CGU: Circuit group unblocking message ................................... 42 A.3.8 CGUA: Circuit group unblocking ACK message....................... 43 A.3.9 CCR: Continuity check request message .................................... 43 A.3.10 REL: Release message ................................................................ 43 A.3.11 RLC: Release circuit message..................................................... 44 A.3.12 RSC: Reset circuit message ........................................................ 44 A.3.13 RES: Resume message................................................................ 45 A.3.14 SUS: Suspend message ............................................................... 45 A.3.15 UBL: Unblocking message ......................................................... 47 A.3.16 UBA: Unblocking ACK message ............................................... 47 B ISUP Parameters............................................................................................... 47 B.1 Access transport ........................................................................................... 47 B.2 Automatic congestion level.......................................................................... 47 B.3 Backward call indicators .............................................................................. 47 B.3.1 Charge indicator .......................................................................... 47 B.3.2 Called party’s status indicator..................................................... 47 B.3.3 Called party’s category indicator ................................................ 47 B.3.4 End-to-end method indicator....................................................... 47 B.3.5 Interworking indicator................................................................. 47 B.3.6 End-to-end information indicator................................................ 48 B.3.7 ISDN User part indicator ............................................................ 48 B.3.8 ISDN access indicator ................................................................. 48 B.3.9 Echo control device indicator...................................................... 48 B.3.10 SCCP method indicator............................................................... 48 B.4 Called party number..................................................................................... 48 B.4.1 Odd/even indicator ...................................................................... 48 B.4.2 Nature of address indicator ......................................................... 48 B.4.3 Internal network number indicator.............................................. 49 B.4.4 Numbering plan indicator ..........................................................
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