July 20, 2000H.323/SIP1 Interworking Between SIP/SDP and H.323 Agenda Compare SIP/H.323 Problems in interworking Possible solutions Conclusion Q/A Kundan N. Singh, Dept. of Computer Science, Columbia University

July 20, 2000H.323/SIP2 What is H.323 ? Q931 H245 RTP RAS H450 Multimedia Communication Protocol H323 Box Terminal/ User Agent Gateway (Bridge to another network) Gatekeeper MCU (Conferencing) Terminal/ User Agent H323 Network

July 20, 2000H.323/SIP3 What is SIP ? Session Initiation Protocol for Internet UserAgent Servers UAS/UAC Registrar Redirect Proxy

July 20, 2000H.323/SIP4 H.323 vs SIP IP and lower layers TCP UDP TPKT Q.931 H.245 RASRTCP RTP Codecs Terminal Control/Devices Transport Layer SIPSDP RTP Codecs RTCP Terminal Control/Devices Typical UserAgent Protocol stack for Internet

July 20, 2000H.323/SIP5 SIP vs H.323 Text based request response SDP (media types and media transport address) Server roles: registrar, proxy, redirect Binary ASN.1 PER encoding Sub-protocols: H.245, H.225 (Q.931, RAS, RTP/RTCP), H.450.x... H.323 Gatekeeper Both use RTP/RTCP over UDP/IP

July 20, 2000H.323/SIP6 Interworking Problems Call setup translation Q.931 SETUP Q.931 CONNECT INVITE 200 OK ACK Terminal Capabilities Open Logical Channel H.323SIP Destination address Media capabilities (audio/video) Media transport address (RTP/RTCP receive) Multi-stage dialing H.323v2 Fast-start is optional

July 20, 2000H.323/SIP7 Interworking Problems User Registration H.323SIP Location independent user identifier ? Use information from both networks H.323 terminal H.323 GatekeeperSIP registrar SIP user agent ? Alias: Henry E164: 7040

July 20, 2000H.323/SIP8 Interworking Problems Media Description H.323/H.245 (declare your exact modes) Translation in both directions Algorithm selection by end-systems Supports inter-media constraints { [G.711 Mu law, G.711 A law][H.261 video]} { [G.723.1] [no video] } SIP/SDP (dynamically choose from listed modes) List of alternative set of algorithms. audio G.711 Mu law, G.723.1, G.728 video H.261

July 20, 2000H.323/SIP9 Interworking Problems Call Services H.323 Conferencing: centralized signaling control, MC (Multi- point Controller) Supplementary services, like call transfer: H.450.x SIP Conferencing: centralized bridged + decentralized distributed New headers : Also, Requested-By, Replaces

July 20, 2000H.323/SIP10 Interworking Problems Security and QoS H.323 uses H.235, whereas SIP uses Basic, Digest, PGP Media Traffic end-to-end; QoS ?

July 20, 2000H.323/SIP11 What we want ? Transparent translation Minimum modification in SIP or H.323 Use features from both SIP and H.323 Direct RTP/RTCP traffic; end-to-end

July 20, 2000H.323/SIP12 User registration Registration info to foreign network H.323 terminal H.323 Gatekeeper + SGW pc1.office.com RRQ Contact: SIP registrar server SIP user agent REGISTER Contact:pc1 INVITE 3xx Moved Contact:pc1 home.com use SIP REGISTER and/or H.323 RRQ/RCF

July 20, 2000H.323/SIP13 User registration Registration info from foreign network use SIP OPTIONS and/or H.323 LRQ/LCF H.323 terminal H.323 Gatekeeper pc1.office.com RRQ Contact: SIP registrar server + SGW SIP user agent LRQ/LCF INVITE 200 OK home.com

July 20, 2000H.323/SIP14 User registration Different Architectures SGW co-located with H.323 gatekeeper SGW co-located with SIP registrar/proxy server Independent SGW

July 20, 2000H.323/SIP15 Call Setup with H.323v2 Fast Start (Almost) One-to-one mapping between SIP and H.323 messages. INVITE 200 OK. ACK Setup/FastStart Connect/FastStart H323SIP RTP/RTCP Reverse direction is similar

July 20, 2000H.323/SIP16 Call Setup without Fast Start Q.931 SETUP Q.931 CONNECT INVITE 200 OK ACK Terminal Capabilities Open Logical Channel H.323SIP Destination address Media capabilities (audio/video) Media transport address (RTP/RTCP receive) Accept the call from H.323, forward to SIP after OLC ? Not desirable.

July 20, 2000H.323/SIP17 Call Setup without Fast Start, SIP to H.323 INVITE 200 OK. ACK Setup/Q931 Connect/Q931 Capabilities/H245 Open Logical Channel/ H245 Capabilities/H245. Signaling Gateway RTP/RTCP H323SIP Acknowledgement Media Transport Address

July 20, 2000H.323/SIP18 Call Setup without Fast Start, H.323 to SIP RTP/RTCP H323SIP INVITE 200 OK ACK Setup/Q931 Connect/Q931 Capability Exchange Open Logical Channel Signaling Gateway Open Logical Channel Re-INVITE/SIP+SDP Acknowledgement Media Transport Address

July 20, 2000H.323/SIP19 Media Capability Modify SIP/SDP : multiple capability sets, or... Let the SGW choose a sub-set of capabilities for SIP side Re-INVITE or change in H.323 mode or logical channels, whenever it changes

July 20, 2000H.323/SIP20 Conclusion What can be done ? What can’t ? Basic audio/video call Transparency of User registration Advanced calls with complex sessions Conferencing SIP centered, H.323 centered Other supplementary services...

July 20, 2000H.323/SIP21 Conclusion Status IETF mailing list Finalizing requirements document IMTC and ETSI TIPHON Convergence between SIP and H.323 in newer versions

July 20, 2000H.323/SIP22 Prototype (free download) system at Other information at My contact info: Conclusion Implementation - sip323