H.323 to SIP Call
In this example, a H.323 terminal calls a SIP-enabled PC through a H.323/SIP gateway. The gateway does signaling translation between the protocols but allows the two end points to exchange media packets directly with each other. The full details of SIP/H.323 interworking are being developed in the SIP working group [4].
In this example, shown in Figure ， the initial message exchange is between the calling H.323 terminal and the H.323 gatekeeper. The gatekeeper resolves the H.323 alias into an address served by the H.323/SIP gateway. The ACF response indicates that gatekeeper-routed signaling is required, so the Q.931 and H.245 TCP connections are opened to the gatekeeper, which opens TCP connections to the gateway. The calling H.323 terminal sends a Q.931 Setup message to the gatekeeper, which proxies it to the H.323/SIP gateway. The gateway then looks up the H.323 alias and resolves it to the SIP URI of the called party. It constructs an INVITE from the Setup message and forwards it to a SIP proxy, which forwards it to the called party. Note that because the Setup message does not contain any media information, the INVITE does not contain any media information either. The called party sends a 180 Ringing then a 200 OK to indicate that the call has been answered. The media information present in the SDP message body is stored by the gateway, which sends Alerting and Connect messages.
Figure 10.6: H.323 to SIP call.
Messages are sent to the gatekeeper, which proxies them to the calling H.323 terminal. The gateway holds off sending the ACK response to the INVITE until the H.245 media exchange is completed between the H.323 terminal and the gateway. Once that is complete, the negotiated media capabilities are returned in the ACK and the media session begins.
M1 ARQ
address(h323alias=Stibitz)
M2 ACF
gatekeeper routed signaling
M3 Setup
Cd address(h323alias=Stibitz)
Cg address(h323alias=Burroughs)
M4 Setup
Cd address(h323alias=Stibitz)
Cg address(h323alias=Burroughs)
M5 ARQ
M6 ACF
M7 INVITE sip:stibitz@proxy.com SIP/2.0
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544 ?TCP used for transport
Max-Forwards: 70
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>
Call-ID: 526272332146783569054
CSeq: 43252 INVITE ?CSeq initialized to 43252
Contact: <sip:burroughs@h323-gateway.com;transport=tcp>
Content-Length: 0
M8 100 Trying
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
From: <sip:burroughs@h323-gateway.com>
To: <sip:stibitz@proxy.com>
Call-ID: 526272332146783569054
CSeq: 43252 INVITE
Content-Length: 0
M9 INVITE sip:gstibitz123@snailmail.com SIP/2.0
Via: SIP/2.0/TCP 3.4.5.6:5060;branch=z9hG4bK452.1
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
Max-Forwards: 69
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>
Call-ID: 526272332146783569054
CSeq: 43252 INVITE
Contact: <sip:burroughs@h323-gateway.com;transport=tcp>
M10 SIP/2.0 180 Ringing
Via: SIP/2.0/TCP 3.4.5.6:5060; branch=z9hG4bK452.1
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>;tag=1926
Call-ID: 526272332146783569054
CSeq: 43252 INVITE
Contact: <sip:gstibitz123@snailmail.com;transport=tcp>
Content-Length: 0
M11 SIP/2.0 180 Ringing
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
From: <sip:burroughs@h323-gateway.com>
To: <sip:stibitz@proxy.com>;tag=1926
Call-ID: 526272332146783569054
CSeq: 43252 INVITE
Contact: <sip:gstibitz123@snailmail.com;transport=tcp>
Content-Length: 0
M12 Alerting
M13 Alerting
M14 SIP/2.0 200 OK
Via: SIP/2.0/TCP 3.4.5.6:5060; branch=z9hG4bK452.1
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>;tag=1926
Call-ID: 526272332146783569054
CSeq: 43252 INVITE
Contact: <sip:gstibitz123@snailmail.com;transport=tcp>
Content-Type: application/sdp
Content-Length: 134
v=0
o=George 2890844576 2890844576 IN IP4 4.30.19.04
s=-
t=0 0
c=IN IP4 4.30.19.04
m=audio 5004 RTP/AVP 0
a=rtpmap:0 PCMU/8000
M15 SIP/2.0 200 OK
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>;tag=1926
Call-ID: 526272332146783569054
CSeq: 43252 INVITE
Contact: <sip:gstibitz123@snailmail.com>
Content-Type: application/sdp
Content-Length: 134
v=0
o=George 2890844576 2890844576 IN IP4 4.30.19.04
s=-
t=0 0
c=IN IP4 4.30.19.04
m=audio 5004 RTP/AVP 0
a=rtpmap:0 PCMU/8000
M16 Connect
M17 Connect
M18 TerminalCapabilitySet
M19 TerminalCapabilitySet
M20 TerminalCapabilitySetAck
M21 TerminalCapabilitySetAck
M22 TerminalCapabilitySet
M23 TerminalCapabilitySet
M24 TerminalCapabilitySetAck
M25 TerminalCapabilitySetAck
M26 MasterSlaveDetermination
M27 MasterSlaveDetermination
M28 MasterSlaveDeterminationAck
M29 MasterSlaveDeterminationAck
M30 OpenLogicalChannel
g711uLaw 1.28.18.57 60002
M31 OpenLogicalChannel
g711uLaw 1.28.18.57 60002
M32 OpenLogicalChannelAck
M33 OpenLogicalChannelAck
Call Flow Examples 181
M34 OpenLogicalChannel
g711uLaw 4.30.19.04 5004
M35 OpenLogicalChannel
g711uLaw 4.30.19.04 5004
M36 OpenLogicalChannelAck
M37 OpenLogicalChannelAck
M38 ACK sip:gstibitz123@snailmail.com SIP/2.0
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK32
Max-Forwards: 70
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>;tag=1926
Call-ID: 526272332146783569054
CSeq: 43252 ACK
Content-Type: application/sdp
Content-Length: 130
v=0
o=- 2890844577 2890844577 IN IP4 1.28.18.57
s=-
t=0 0
c=IN IP4 1.28.18.57
m=audio 60002 RTP/AVP 0
a=rtpmap:0 PCMU/8000
M39 ACK sip:gstibitz123@snailmail.com SIP/2.0
Via: SIP/2.0/TCP 3.4.5.6:5060;branch=z9hG4bK452.1
Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK532
Max-Forwards: 69
From: <sip:burroughs@h323-gateway.com>;tag=3q526g45
To: <sip:stibitz@proxy.com>;tag=1926
Call-ID: 526272332146783569054
CSeq: 43252 ACK
Content-Type: application/sdp
Content-Length: 130
v=0
o=- 2890844577 2890844577 IN IP4 1.28.18.57
s=-
t=0 0
c=IN IP4 1.28.18.57
m=audio 60002 RTP/AVP 0
a=rtpmap:0 PCMU/8000
