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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
Agenda
Overview
Target network and goal
Signaling protocols and comparison
Design
Implementation
Performance evaluation
Discussion
Related work
Conclusion
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)
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.
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
Signal Protocols -Comparison of H.323 and SIP(cont.)
Advertising Conference information availability
Determination of conference media capabilityApplicable 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
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
Design – Key Design DecisionsConference Call Messages Translation
H.323 SIP
Conference Create - H.225 SETUP (? H.245 CapSet ) SDP message N/A (no SAP supported) SDP message
Conference Invite - depend on conferencing scenariosdepend 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)
Design – Key Design Decisions(Cont.)
Central Determination of Conference Media Capability
Ongoing Conference Information
Conference Management: Membership Control and Session Management
Design – Example: Conference Invite and Join
H.323 Endpoint (E1) GCCG SIP Client C1
Setup (C1 {usrID@addr}, CID = N, invite,FastStart {openLogicalChannel structures})
Alerting/Call Proceeding
ARQ
ACF
Connect (GCCG H.245 TA)
Ringing
Accept
Invite ( C1 {usrID}, Session Info)
Bye
Terminal Left Conference
No H.245 control channel…
Option ( C1 {usrID})
Option_Reply(Media type)
SDP messages to MBone cloud
• H.323 Client Invites SIP Client via Fast Connection Procedure
NOTE: Conference is created after the invitee’s media cap is received.
Design – Example: Conference Invite and Join (Cont.)
H.323 Endpoint (E2) GCCG H.323 Participants (E1)
Setup (GCCG, CID = N or session name, Join)
Alerting/Call Proceeding
ARQ
ACF
Connect (GCCG H.245 TA)
terminalCapabilitySet Exchange
Master/Slave Determination
CommunicationModeCommand
MultipointConference Indication MultipointConference Indication
CommunicationModeCommand
• A H.323 Endpoint joins an ongoing conference.
Implementation
RASSignalingChannel
Handler
Call SignalingRouting
Handler
H.323 connectionper endpoint
H.225Call Signal
Channel
Handler
H.245Call Control
Channel
Handler
ConferenceControl
Logics/Functions
SIP/SDPMessage
HandlerTranslated SignalFIFO Queues
H.323Message
Handler
InternalConference
Control Data
Media DataSwitching
Internal Data Flow
Active Thread
Program Control Interaction
Internal Data Storage
Internal Message Queue
SDPReceive
Handler
SDP/SIPSend
Handler
SIPReceive
Handler
GCCG Internal Architecture
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.
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
Performance Evaluation (cont.)
GCCGServer
H.323client
H.323client
H.323client
H.323client
H.323client
RTTMeasurement
Media StreamsRTP(H.261)
GCCGServer
SIPclient
H.323client
SIPclient
SIPclient
SIPclient
RTTMeasurement
Media StreamsRTP(H.261)
multicast
Performance Evaluation (cont.)
6
8
10
12
14
16
18
1 2 3 4 5Number of Participants
Ave
rage
RTT
(ms)
Scenario 1(H.323 clients)
Scenario 2(SIP clients)
Comparison of Average RTT
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?
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?
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
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
Conclusion
Completion of interoperability for H323 and SIP in multiparty media conferencing sessions
Recommendation for raised interoperability issues.