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 -Generic H.323 Call Flow

Signal Protocols -Generic SIP Call Flow

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 – GCCG Functionality

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.

Q & A