例子：H.323到SIP的呼叫

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:[email protected] SIP/2.0
     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544    ↞TCP used for transport
     Max-Forwards: 70
     From: <sip:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE                              ↞CSeq initialized to 43252
     Contact: <sip:[email protected];transport=tcp>
     Content-Length: 0
M8   100 Trying
     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544
     From: <sip:[email protected]>
     To: <sip:[email protected]>
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE
     Content-Length: 0


M9   INVITE sip:[email protected] 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:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE
     Contact: <sip:[email protected];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:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>;tag=1926
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE
     Contact: <sip:[email protected];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:[email protected]>
     To: <sip:[email protected]>;tag=1926
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE
     Contact: <sip:[email protected];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:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>;tag=1926
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE
     Contact: <sip:[email protected];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:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>;tag=1926
     Call-ID: 526272332146783569054
     CSeq: 43252 INVITE
     Contact: <sip:[email protected]>
     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:[email protected] SIP/2.0
     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK32
     Max-Forwards: 70
     From: <sip:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>;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:[email protected] 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:[email protected]>;tag=3q526g45
     To: <sip:[email protected]>;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