Interworking Between SIP/SDP and H.323 Kundan Singh and

Interworking Between SIP/SDP and H.323 Kundan Singh and Henning Schulzrinne IRT Lab, Dept. of Computer Science Columbia University New York, USA [email protected]

SIP vs H.323 Text-based (HTTP-like) 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.332, H.450.x. H.323 Gatekeeper Both use RTP/RTCP over UDP/IP

Interworking Problems H.323 Q.931 SETUP Call setup translation Destination address SIP INVITE Q.931 CONNECT Terminal Capabilities Terminal Capabilities 200 OK Media capabilities ACK Open Logical Channel Open Logical Channel Media transport address Multi-stage dialing H.323v2 Fast-start is optional

Interworking Problems User Registration H.323 SIP ? H.323 Gatekeeper H.323 terminal SIP registrar SIP user agent Location independent user identifier ? Use information from both networks

Interworking Problems Media Description H.323/H.245 Supports inter-media constraints { [G.711 Mu law, G.711 A law][H.261 video]} { [G.723.1] [no video] } SIP/SDP List of alternative set of algorithms. audio G.711 µ-law, G.723.1, G.728 video H.261 Translation in both directions Algorithm selection by end-systems

Interworking Problems Advanced Services H.323 conferencing: centralized signaling control, MC (Multipoint Controller) Supplementary services: H.450.x SIP conferencing: centralized bridged full mesh multicast New headers : Also, Requested-By, Replaces

User registration Registration info to foreign network Three ways: SGW GK, SGW proxy/registrar, SGW REGISTER [email protected] Contact:sgw H.323 Gatekeeper SGW sgw.columbia.edu RRQ [email protected] Contact:128.59.19.200 H.323 terminal SIP registrar server INVITE [email protected] 3xx Moved Contact:sgw SIP user agent 128.59.19.200 Independent SGW preferable - use SIP OPTIONS and H.323 LRQ

Call Setup with H.323v2 Fast Start One-to-one mapping between SIP and H.323 messages. H323 SIP Setup/FastStart INVITE 200 OK Connect/FastStart ACK RTP/RTCP Reverse direction is similar

Call Setup without Fast Start, SIP to H.323 H323 SIP Setup/Q931 Connect/Q931 INVITE Signaling Gateway Capabilities/H245 Capabilities/ H245. Open Logical Channel/ H245 Acknowledgement Media Transport Address 200 OK. ACK Open Logical Channel / H245 Acknowledgement RTP/RTCP

Call Setup without Fast Start, H.323 to SIP H323 SIP Setup/Q931 Connect/Q931 INVITE Signaling Gateway ACK Capability Exchange Open Logical Channel 200 OK Media Transport Address Acknowledgement Open Logical Channel Acknowledgement RTP/RTCP Re-INVITE/SIP SDP

Capability Set Capability set in each direction Maximal intersection and current operating modes Re-INVITE or change in H.323 mode or logical channels, whenever it changes Example: C1 { [PCMU, PCMA, G.723.1] [H.261] } C2 { [PCMU, PCMA, G.729] [H.261] } C1 C2 {[PCMU, PCMA] [H.261]} operating modes [audio PCMU,video H.261]

Conclusion and Future Work Ad-hoc conferencing SIP-centered or H.323-centered conferencing Basic call setup other supplementary services Initial implementation: openh323 Columbia stack for basic audio call efforts in IETF (SIP WG task force), ITU and ETSI TIPHON Convergence between SIP and H.323 in newer versions (fastStart, UDP)