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.
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
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
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 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.
15. Implementation
RAS
Signaling
Channel
Handler
Call Signaling
Routing
Handler
H.323 connection
per endpoint
H.225
Call Signal
Channel
Handler
H.245
Call Control
Channel
Handler
Conference
Control
Logics/Functions
SIP/SDP
Message
HandlerTranslated Signal
FIFO Queues
H.323
Message
Handler
Internal
Conference
Control Data
Media Data
Switching
Internal Data Flow
Active Thread
Program Control Interaction
Internal Data Storage
Internal Message Queue
SDP
Receive
Handler
SDP/SIP
Send
Handler
SIP
Receive
Handler
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
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
Requirements to integrate cross-domain call signaling in transparency
Then is the proposed solution
Based on the solution, what kinds of co-operation scenarios it can support
At last, the functionality of the key component in our solution will be presented.
The first requirement is call signaling mapping, translation and semantics adaptation.
The most remarkable semantic in this project is call establishment.
The following is call signaling messages and semantics mapping between H.323 and SIP protocol
H.323 SETUP-JOIN message maps to no SIP message but…
IGMP message should be sent to a corresponding multicast router demon in order to forward the media streams from that ongoing MBone session.
NOTE: if a SIP client participates in a conference created by an H.323 client, the conference must have at least two H.323 clients
Three exceptions
Wait for the first joining H.323 client to determine common media communication modes
2.SETUP message contains media data types of that inviting terminal
3.In order to invite other client join that session or joins that session by itself