1. A Conference Gateway Supporting Interoperability Between SIP and H.323 Jiann-Min Ho (Presenter) Jia-Cheng Hu Information Networking Institute Peter Steenkiste School of Computer Science Dept. of Electrical and Computer Engineering Carnegie Mellon University

2. Agenda Overview Target network and goal Signaling protocols and comparison Design Implementation Performance evaluation Discussion Related work Conclusion

3. Overview - Multi-party Media Conference Media conference application drivers Network bandwidth and endpoint capability Signaling and media streaming protocols Signaling protocols: H.323 (ITU-T) vs. SIP (IETF) Media transport protocol: RTP (RFC1889)

4. Target Network and Goal Target network – Packet switching network (e.g. IP), not PSTN Future network infrastructure Goal – two folds Build a practical system allowing SIP and H.323 clients to participate in one video conferencing session. A set of recommendations and for developers and standard bodies that would improve interoperability issues.

5. Signal Protocols - Generic H.323 Call Flow

6. Signal Protocols - Generic SIP Call Flow

7. Signal Protocols - Comparison of H.323 and SIP Modularity Synchronization of the mapping procedures during operation Message presentation Translation of syntax Mapping of an H.323 conference and a SIP session Map H.323 conference ID and SIP session ID Map the H.245 capabilityDescriptor structure to SDP syntax

8. Signal Protocols - Comparison of H.323 and SIP(cont.) Advertising Conference information availability Determination of conference media capability Applicable solution: Central determination via an intermediate agent serving as an H.323 mc Control over membership Generic admission control mechanisms and strategies handling conference membership

9. Design – GCCG Functionality

10. Design - Functionality of GCCG in SIP and H.323 perspective On the H.323 side Gatekeeper (GK), Multipoint Controller (MC) and Multipoint Processor (MP) without transcoding Independent conferencing components On the SIP side Proxy Server and Conferencing Server

11. Design – Key Design Decisions Conference Call Messages Translation H.323  SIP Conference Create - H.225 SETUP (? H.245 CapSet )  SDP message N/A (no SAP supported)  SDP message depend on conferencing scenarios Conference Invite - depend on conferencing scenarios H.225 SETUP  INVITE (? SDP) message (? FastStart)+ OPTION ( obtain/check SIP invitee Media Cap. - Invitable? ) H.225 SETUP  INVITE (SDP) message Conference Join - H.225 SETUP  N/A (trigger IGMP message) N/A  N/A (only IGMP message)

12. Design – Key Design Decisions (Cont.) Central Determination of Conference Media Capability Ongoing Conference Information Conference Management: Membership Control and Session Management

13. Design – Example: Conference Invite and Join H.323 Client Invites SIP Client via Fast Connection Procedure NOTE: Conference is created after the invitee’s media cap is received.

14. Design – Example: Conference Invite and Join (Cont.) A H.323 Endpoint joins an ongoing conference.

15. Implementation GCCG Internal Architecture

16. Implementation – Operation and Status Only video is available. Simple Conference Media Mode Determination H.323 clients are lack of conference information, LDAP is not supported. Media streams (RTP) are forwarded via GCCG; no support from media mixing/transcoding components/gateways.

17. Performance Evaluation Correctness of conferencing signaling flow via GCCG Testbed configuration One GCCG Server (Linux PC) and Five PC Clients (NT) Video Conferencing Software MS NetMeeting version 3.01 and the MBone tools SDR v2.9 and VIC v2.8. Common communication mode - H.261 Network Configuration 10 Mbs shared Ethernet

18. Performance Evaluation (cont.)

19. Comparison of Average RTT

20. Discussion Negotiation of Media Capabilities Common conference media type (no transcoding GW) H.323 – determined by MC via H.245 procedures SIP – use a proxy server to query media capability information. OPTION message can be applied. Standard? Draft? Translation of message syntax between H.245 and SDP Change of media stream codec gracefully?

21. Discussion (cont.) Session Advertising Conference information advertisement SIP – operate with SAP (push) H.323 – LDAP can be used (pull) if clients require this feature Conference information mapping Adaptation of Call Signaling Semantics Reduce signaling overhead via H.323 FastConnect Conference Control H.323 – ITU-T T series, e.g. T.124, GCCP… SIP – drafting, standards?

22. Discussion (cont.) IP Multicast Characteristic of the architecture – open conference Authorization, authentication, encryption Application level support – conference server (GCCG) and clients (H.323/SIP) IP multicast support – match application needs Access media streaming multicast address H.323 – determined by MC SIP – from SAP messages malloc

23. Related Work Several active groups, e.g. aHIT! from IMTC, ITU-T SG 16 and TIPHON, and … H.323/SIP signaling gateway - Columbia University Our prototype implementation focus Multi-party media conferencing signaling support IP multicast efficiency

24. Conclusion Completion of interoperability for H323 and SIP in multiparty media conferencing sessions Recommendation for raised interoperability issues.

25. Q & A