1. RFC-4123 SIP-H.323 Interworking Requirements
Speaker: Yan-Shiang Wang
Adviser: Quincy Wu
Date: 2005/12/22

2. H.323 Introduction Terminal Gateway Gatekeeper
Endpoint that offers real-time communications with other h.323 endpoint
Gateway
Translation services between the h.323 and others
Gatekeeper
Controller
MCU (Multipoint Control Unit)
Endpoint that manages multipoint conferences

3. H.323 Zone Terminal Terminal Gatekeeper Terminal Terminal Gateway MCU
Router
SIP
H.323
PSTN

4. H.323 Protocol H.225.0 H.245 RAS: Registration, Admission, Status
Between endpoints and gatekeepers
Q.931: ISDN Layer 3 signaling protocol
Between endpoints
H.245
Establish and control media streams
Between two or more endpoints

5. Terminal/Application Control
H.323 Protocol Stack
Audio/Video
Application
Terminal/Application Control
Codecs
RTCP
H.225.0
RAS
Signaling
Call (Q.931)
H.245
Control
RTP
UDP
TCP
Network Layer
Data Link Layer
Physical Layer

6. H.323 Protocol (cont.) Gatekeeper Q.931 Audio codec Video codec
Discovery: udp port 1718
RAS: udp port 1719
Q.931
udp or tcp port 1720
Audio codec
G.711, G.722, G.723, G.728, G.729
Video codec
H.261, H.263

7. RAS Signaling - Discovery
Terminal
Gatekeeper
Gatekeeper
GRQ
GRQ
GK discovery multicast address
GRQ
GRJ
GCF
GRQ: Gatekeeper Request　GRJ: Gatekeeper Reject　GCF: Gatekeeper Confirm
Terminal sends just one GRQ to the Gatekeeper discovery multicast address. Therefore, the Terminal will now proceed to register with which Gatekeeper.

8. RAS Signaling - Registration
Terminal
Gatekeeper
RRQ
RCF ／／ ／／
URQ
UCF
RRQ: Registration Request　　RCF: Registration Confirm URQ: Unregistration Request　UCF: Unregistration Confirm

9. RAS Signaling - Admission
Terminal
Gatekeeper
Terminal
ARQ
ACF
Setup
ARQ
ACF ／／ ／／ ／／
DRQ
DRQ
DCF
DCF
ARQ: Admission Request　ACF: Admission Confirm DRQ: Disengage Request　DCF: Disengage Confirm

10. Q.931 Signaling Terminal Terminal Setup Call Proceeding Alerting
Connect
H.245 Session Establishment
Media Exchange
H.245 Session Release
Release Complete

11. Direct Endpoint Call Gatekeeper Terminal Terminal Gatekeeper ARQ ACF
Setup
Call Proceeding
ARQ
ACF
Alerting
Connect
H.245 Session Establishment
Media Exchange
H.245 Session Release
Release Complete
DRQ
DRQ
DCF
DCF

12. H.245 Signaling TCS: Terminal Capability Set
MSD: Master Salve Determination
TCSA: TCS Ack
MSDA: MSD Ack
OLC: Open Logical Channel
OLCA: OLC Ack
OLCC: OLC Confirm
ESC: End Session Command

13. H.245 Procedure Terminal Terminal TCS MSD
Both Terminal send information signalling
at the same time, they
don’t need to wait
Ack signalling.
TCS　MSD
TCSA　MSDA
TCSA　MSDA
OLC
OLC
OLCA
OLCA
OLCC
RTP　RTCP
ESC
ESC

14. H.245 Procedure - Fast Connect
Terminal
Terminal
Setup (faststart [logical channel info])
Call Proceeding
Alerting
Connect (faststart [logical channel info])
Media Exchange
Release Complete

15. H.323 detailed header info

16. H Q.931 header

17. H.245 - Master Slave Determination
Terminal Type Value
General terminal = 50
Gateway = 60
MCU = 190
MCU (currently managing a conference) = 240
Status Determination Number
Random
Largest one is master

18. H MSD (cont.)

19. H OLC, OLCA, OLCR

20. SIP-H.323 Interworking IWF (Interworking Function)
interworking between H.323 and SIP
MSF (Media-Switching Fabric)
optional entity within the IWF
switches media such as voice, video, or fax from one network association to another

21. SIP-H.323 IWF H.323 Endpoint SIP User Agent H.323 Terminal SIP User
Gatekeeper
SIP
Server
MCF
H.323
MCU
SIP-H.323 IWF

22. SIP-H.323 IWF (cont.) May be integrated into an H.323 GK or SIP server
Simply forwards media packets without modification
Should not process media
MSF - Convert media from one encoding or format to another
Out of scope for SIP-H.323 protocol translation

23. General Interworking Requirements
Opening of logical channels
Should support the seamless exchange
Should support open media channels
The channel can be opened at the MSF of the IWF
When endpoints can’t open media channels themself
IWF H.323 features
Should support fast connect
Should support pre-granted ARQ (IWF in GK)
Overlapped sending
Follow RFC3578 (from H.323)
Q.931 (from SIP)

24. Overlap Signalling Modern switches use en-bloc signalling
Some parts of the PSTN still use overlap signalling
Sending only some digits of the callee's number in the first signalling message
Further digits are sent in subsequent signalling messages

25. Interworking Analysis
simple call setup
mapping addresses
finding a subset of capabilities described by H.245 and SDP
conferencing and call services
security and authentication

26. Register (IWF colocated with SIP server)
H.323 Terminal
Gatekeeper
IWF/GW
SIP UA
RRQ
RCF
RRQ
RCF
REGISTER
RRQ
RCF
200 OK

27. RRQ (IWF colocated with H.323 GK)
H.323 Terminal
IWF/GW
SIP Server
SIP UA
RRQ
REGISTER
200 OK
RCF
REGISTER
200 OK

28. Invite (IWF colocated with SIP server)
H.323 Terminal
Gatekeeper
IWF/GW
SIP UA
INVITE
100 Trying
ARQ
ACF
Setup
Call Proceeding
ARQ
ACF
Alerting
180 Ringing
Connect
H.245　Signaling
200 OK
ACK
RTP　RTCP

29. Setup (IWF colocated with H.323 GK)
H.323 Terminal
IWF/GW
SIP Server
SIP UA
ARQ
ACF
Setup
Call Proceeding
INVITE
INVITE
100 Trying
180 Ringing
180 Ringing
Alerting
200 OK
200 OK
Connect
negotiate between 200 OK and ACK
H.245　Signaling
ACK
ACK
RTP　RTCP

30. Call from SIP to H.323 INVITE Setup Connect (no faststart)
H.323 Terminal
IWF/GW
SIP UA
INVITE
Setup
Connect (no faststart)
TCS (g711Ulaw)
TCSAck
TCS (g711Alaw & g711Ulaw)
TCSAck
200 OK
c=IN IP
m=audio 5000 RTP/AVP 0
OLC (g711Ulaw)
OLCAck( :5000)
ACK
OLC (g711Ulaw)
OLCAck( :9000)
RTP　RTCP

31. Call from SIP to H.323 (with faststart)
H.323 Terminal
IWF/GW
SIP UA
INVITE
c=IN IP
m=audio 9000 RTP/AVP 0
Setup
faststart={g711Ulaw,Tx},
{g711Ulaw,Rx, :9000}
200 OK
c=IN IP
m=audio 5000 RTP/AVP 0
Connect
faststart=
{g711Ulaw,Tx, :5000}
{g711Ulaw,Rx}
ACK
RTP　RTCP

32. Call from H.323 to SIP Setup (no faststart) INVITE 180 Ringing 200 OK
H.323 Terminal
IWF/GW
SIP UA
Setup (no faststart)
INVITE
180 Ringing
200 OK
Connect
TCS (g711Alaw)
TCSAck
TCS (g711Alaw & g711Ulaw)
TCSAck
ACK with updated SDP
c=IN IP
m=audio 5000 RTP/AVP 8
OLC (g711Alaw)
OLCAck( :5000)
OLC (g711Alaw)
OLCAck( :9000)
RTP　RTCP

33. Call from H.323 to SIP (with faststart)
H.323 Terminal
IWF/GW
SIP UA
Setup
faststart={g711Ulaw,Tx},
{g711Ulaw,Rx, :5000}
INVITE
c=IN IP
m=audio 5000 RTP/AVP 0
200 OK
c=IN IP
m=audio 9000 RTP/AVP 0
Connect
faststart=
{g711Ulaw,Tx, :9000}
{g711Ulaw,Rx}
ACK
RTP　RTCP

34. Mapping Addresses SIP address format
SIP-Address = (name-addr j addr-spec)
name-addr = [display-name] ”<” addr-spec ”>”
addr-spec = SIP-URL
SIP-URL = ”sip:” [ userinfo ] hostport url-parameters 　[headers]
userinfo = user [ ”:” password ]
hostport = host [ ”:” port ]
host = hostname j IPv4address
url-parameters = *(”;” url-parameter)
url-parameter = user-param j . . .

35. Mapping Addresses (cont.)
H323 address format {
　e164 IA5String (SIZE(1..128)) (FROM(" \#*,")),
　h323-ID BMPString (SIZE (1..256)), ...,
　url-ID IA5String ( SIZE( )),-- URL Style address
　transport-ID TransportAddress, -- IPv4, IPv6, IPX etc.,...
　 -ID IA5String (SIZE(1..512)),
　partyNumber PartyNumber }

36. SIP to H323 h323-ID e164 url-ID email-ID transport-ID
SIP-Address -> addr-spec
exceeds 256 characters -> 414 (Address Too Long)
e164
“+”, “-” are removed
“p” -> “,”
url-ID
exceeds 512 characters -> 414 (Address Too Long)
-ID
transport-ID
If host is indicated as a dotted quad

37. SIP to H323 - examples
SIP - is converted to an H { }
SIP - user=phone” H.323 – { e164=” ”, }
SIP - H { tranport-ID= IPAddress :1720, }
SIP - “A. Bell H { h323-ID=”A.Bell -ID=“A. Bell }

38. Mapping Addresses - H323 to SIP
If a url-ID is present and it is a SIP-URL
If an h323-ID is present and it can be parsed as a valid SIP-Address, it is used
If the transport-ID is present and it does not identify the IWF, then it forms the hostport portion of the SIP URL and the user portion is constructed using h323-ID or e164
If the -ID is present, then it is used in the SIP-URI

39. Security Considerations
Signaling security for H.323 is described in H.235
The IWF terminates not only the signaling protocols but also the security in each domain
Users at endpoints have to trust the IWF
The IWF must not indicate the identity of a user on one side without first performing authentication

40. Reference SIP-H.323 Signaling Gateway
Interworking Between SIP/SDP and H.323
Mapping of ISUP Overlap Signalling to SIP
Carrier Grade Voice Over IP
Chapter 4, 5