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Interworking Between SIP/SDP and H.323

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RTP and RTCP are carried directly between endsystems, since both endsystems know about the media transport address of the other. Without Fast start in H.323 to SIP ... – PowerPoint PPT presentation

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Title: Interworking Between SIP/SDP and H.323


1
Interworking Between SIP/SDP and H.323
Kundan N. Singh, Dept. of Computer Science,
Columbia University kns10_at_cs.columbia.edu
  • Agenda
  • Compare SIP/H.323
  • Problems in interworking
  • Possible solutions
  • Conclusion
  • Q/A

2
What is H.323 ?
Multimedia Communication Protocol
Terminal/ User Agent
Gatekeeper
Terminal/ User Agent
Q931 H245 RTP RAS H450
Gateway (Bridge to another network)
MCU (Conferencing)
H323 Box
H323 Network
3
What is SIP ?
Session Initiation Protocol for Internet
Registrar Redirect Proxy
Servers
UserAgent
UAS/UAC
4
H.323 vs SIP
Typical UserAgent Protocol stack for Internet
Terminal Control/Devices
Terminal Control/Devices
Q.931
H.245
RTCP
RAS
RTCP
SIP
SDP
Codecs
Codecs
RTP
RTP
TPKT
TCP
UDP
Transport Layer
IP and lower layers
5
SIP vs H.323
  • Binary ASN.1 PER encoding
  • Sub-protocols H.245, H.225 (Q.931, RAS,
    RTP/RTCP), H.450.x...
  • H.323 Gatekeeper
  • Text based request response
  • SDP (media types and media transport address)
  • Server roles registrar, proxy, redirect

Both use RTP/RTCP over UDP/IP
6
Interworking Problems Call setup translation
H.323
SIP
Q.931 SETUP
INVITE
Destination address (Bob_at_office.com)
Q.931 CONNECT
200 OK
Terminal Capabilities
Media capabilities (audio/video)
Terminal Capabilities
ACK
Open Logical Channel
Media transport address (RTP/RTCP receive)
Open Logical Channel
  • Multi-stage dialing
  • H.323v2 Fast-start is optional

7
Interworking Problems User Registration
?
H.323
SIP
Alias Henry E164 7040
sipsam_at_home.com sip7063_at_gateway.com
  • Location independent user identifier ?
  • Use information from both networks

8
Interworking Problems Media Description
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
H.323/H.245 (declare your exact modes)
Supports inter-media constraints G.711 Mu
law, G.711 A lawH.261 video G.723.1 no
video
  • Translation in both directions
  • Algorithm selection by end-systems

9
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

10
Interworking Problems Security and QoS
  • H.323 uses H.235, whereas SIP uses Basic, Digest,
    PGP
  • Media Traffic end-to-end QoS ?

11
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

12
User registration Registration info to foreign
network
REGISTER henry_at_office.com Contactpc1
home.com
INVITE henry_at_office.com
3xx Moved Contactpc1
RRQ henry_at_office.com Contact128.59.19.200
sam_at_home.com
use SIP REGISTER and/or H.323 RRQ/RCF
13
User registration Registration info from foreign
network
LRQ/LCF
home.com
INVITE henry_at_office.com
200 OK
RRQ henry_at_office.com Contact128.59.19.200
sam_at_home.com
use SIP OPTIONS and/or H.323 LRQ/LCF
14
User registration Different Architectures
  • SGW co-located with H.323 gatekeeper
  • SGW co-located with SIP registrar/proxy server
  • Independent SGW

15
Call Setup with H.323v2 Fast Start
(Almost) One-to-one mapping between SIP and H.323
messages.
H323
SIP
Setup/FastStart
INVITE
Connect/FastStart
Reverse direction is similar
16
Call Setup without Fast Start
H.323
SIP
Q.931 SETUP
INVITE
Destination address (Bob_at_office.com)
Q.931 CONNECT
200 OK
Terminal Capabilities
Media capabilities (audio/video)
Terminal Capabilities
ACK
Open Logical Channel
Media transport address (RTP/RTCP receive)
Open Logical Channel
Accept the call from H.323, forward to SIP after
OLC ? Not desirable.
17
Call Setup without Fast Start, SIP to H.323
H323
SIP
Setup/Q931
INVITE
Signaling Gateway
Connect/Q931
Capabilities/H245
Capabilities/H245.
Media Transport Address
200 OK.
Open Logical Channel/ H245
ACK
Open Logical Channel / H245
18
Call Setup without Fast Start, H.323 to SIP
H323
SIP
Setup/Q931
INVITE
Signaling Gateway
200 OK
Connect/Q931
ACK
Capability Exchange
Media Transport Address
Open Logical Channel
Re-INVITE/SIPSDP
19
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

20
Conclusion What can be done ? What cant ?
  • Basic audio/video call
  • Transparency of User registration
  • Advanced calls with complex sessions
  • Conferencing
  • SIP centered, H.323 centered
  • Other supplementary services
  • . . .

21
Conclusion Status
  • IETF mailing list sip-h323_at_egroups.com.
    Finalizing requirements document
  • IMTC and ETSI TIPHON
  • Convergence between SIP and H.323 in newer
    versions

22
Conclusion Implementation - sip323
  • Prototype (free download) system at
    http//www.cs.columbia.edu/kns10/software/gw
  • Other information at http//www.cs.columbia.edu/k
    ns10/research/gw
  • My contact info kns10_at_cs.columbia.edu
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