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 ProblemsCall 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 ProblemsUser 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 ProblemsMedia 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 ProblemsCall 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 ProblemsSecurity 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 registrationRegistration 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
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User registrationRegistration 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 registrationDifferent Architectures

• SGW co-located with H.323 gatekeeper
• SGW co-located with SIP registrar/proxy server
• Independent SGW

15
Call Setupwith 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
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Call Setupwithout 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.
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Call Setupwithout 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
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Call Setupwithout 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
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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
ConclusionWhat 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
ConclusionStatus

• 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
ConclusionImplementation - 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