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Gonzalo Camarillo

SIP / ISUP interconnection. Gonzalo Camarillo. Gonzalo.Camarillo@ericsson.com. ASRL Advanced Signalling Research Lab. Telephone Services. GSTN (General Switched Telephone Network). IP Telephony. IP Telephony. GSTN. Contents. Brief SS7 introduction (architecture).

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Gonzalo Camarillo

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  1. SIP / ISUP interconnection Gonzalo Camarillo Gonzalo.Camarillo@ericsson.com ASRL Advanced Signalling Research Lab.

  2. Telephone Services • GSTN (General Switched Telephone Network) • IP Telephony IP Telephony GSTN

  3. Contents • Brief SS7 introduction (architecture) • Gateway architecture ( SG, MGC, MG ) • ISUP - SIP interworking issues and proposed solutions

  4. Different architectures GSTN architecture: Intelligence in the network Dumb terminals SIP architecture: Move the intelligence to the edge

  5. Signalling in GSTN Signalling in the network (between switches) User to network signalling DSS 1 ISUP DSS 1

  6. DSS-1 Q. 931 Protocol between the user and the network Much simpler than ISUP. Q. 921 Handles the transport of the messages

  7. Signalling in GSTN SS7 (System Signalling No. 7)

  8. General ISUP<->SIP Conversion Voice Stream Signalling SG SIP Server ISUP/MTP STP ISUP/IP SIP SIP MGC IP network SIP MGCP SS7 SIP Client MG DSS 1 E1/T1 RTP

  9. Architecture of the distributed gateway ISUP Signalling Gateway IP side ISUP/IP GSTN side SIP Media Gateway Controller MGCP Voice stream Voice stream Media Gateway

  10. Signalling Gateway Function: • To find the appropriate media gateway controller Signalling GW ISUP ISUP/IP ISUP/IP ISUP/IP ISUP/IP MGC MGC MGC MGC MGCP SIP MGCP SIP MGCP SIP MGCP SIP

  11. Media Gateway Mapping between different voice formats Control Protocol GSTN RTP

  12. Media Gateway Controller for distributedMedia Gateways Functions • Actual mapping between protocols (ISUP-SIP) • Control the Media Gateway/s • Authentication, Authorization and Accounting (AAA)

  13. Experiences implementing ISUP to SIP mapping • Different flavours of ISUP (message flow) • Overlap signalling (SAMs) • In band announcements and ring-back tone • ISUP transparency • Billing in forwarding situations • Tracing calls (malicious, SOS)

  14. Different message flows ITU ISUP message exchange during a call ANSI ISUP: CPG before ACM

  15. Overlap signalling (SAMs) European phone numbers does not have a fixed length. Example: +358 9 299 1 Finland Helsinki Ericsson Front desk +358 9 299 3371 Finland Helsinki Ericsson Camarillo’s The ingress gateway cannot know when the number is complete.

  16. Proposed solution • Ingress gateway waits for SAMs with more digits • a certain amount of time. • Timer = 0 • Heavy signalling traffic may be generated • Timer = 5 secs ( inter-digit timeout) • User is not that patient

  17. In-band announcements and ring-back tones • ‘Your call is being forwarded to an automatic voice mail’ • Ring-back tone • Busy tone Proposed solution: 183 SIP response SIP Client MG DSS 1 E1/T1 RTP

  18. IP network ISUP transparency(SIP bridging) Voice Stream SG SG Signalling ISUP/MTP ISUP/MTP ISUP/IP ISUP/IP SIP MGC MGC STP STP MGCP MGCP E1/T1 RTP E1/T1 MG MG

  19. ISUP transparecy( SIP bridging) ISUP messages in SIP bodies (MIME), SIP INFO method, reliable 1xx responses ... Trusted parties, confidentiality, ISUP flavours...

  20. Billingscenarious Isabel calls from Spain to my GSM mobile: +358 40 702 35 35 (Finland’s international prefix) Isabel pays the call leg Spain-Finland I pay the call leg Finland-Atlanta SIP is end to end … where are the call legs??

  21. Tracing calls • SOS services ( physically closest center ) • Malicious calls An IP address or a SIP URL do not give any useful information for catching the “bad guys”.

  22. Further information IETF internet drafts ( www.ietf.org ) • draft-ietf-sigtran-mime-isup-00.txt • draft-ietf-mmusic-sip-multipart-00.txt • draft-zimmerer-mmusic-sip-isup-mime-00.txt • draft-ietf-mmusic-sip-info-method-01.txt • draft-ietf-mmusic-sip-100rel-00.txt • draft-roach-mmusic-sip-provisional-media-00.txt • draft-donovan-mmusic-183-00.txt • draft-roach-mmusic-sip-pstn-require-header-00.txt • draf-zimmerer-mmusic-sip-bcp-t-00.txt • draft-roach-sip-isup-parameters-00.txt • draft-camarillo-mmusic-sip-isup-bcp.txt

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