H.323到SIP的呼叫

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 signalingM3   Setup     Cd address(h323alias=Stibitz)     Cg address(h323alias=Burroughs)M4   Setup     Cd address(h323alias=Stibitz)     Cg address(h323alias=Burroughs)M5   ARQM6   ACFM7   INVITE sip:[e-mail] SIP/2.0     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544    ↞TCP used for transport     Max-Forwards: 70     From: <sip:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>     Call-ID: 526272332146783569054     CSeq: 43252 INVITE                              ↞CSeq initialized to 43252     Contact: <sip:[e-mail];transport=tcp>     Content-Length: 0M8   100 Trying     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544     From: <sip:[e-mail]>     To: <sip:[e-mail]>     Call-ID: 526272332146783569054     CSeq: 43252 INVITE     Content-Length: 0M9   INVITE sip:[e-mail] 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:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>     Call-ID: 526272332146783569054     CSeq: 43252 INVITE     Contact: <sip:[e-mail];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:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>;tag=1926     Call-ID: 526272332146783569054     CSeq: 43252 INVITE     Contact: <sip:[e-mail];transport=tcp>     Content-Length: 0M11  SIP/2.0 180 Ringing     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544     From: <sip:[e-mail]>     To: <sip:[e-mail]>;tag=1926     Call-ID: 526272332146783569054     CSeq: 43252 INVITE     Contact: <sip:[e-mail];transport=tcp>     Content-Length: 0M12  AlertingM13  AlertingM14  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:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>;tag=1926     Call-ID: 526272332146783569054     CSeq: 43252 INVITE     Contact: <sip:[e-mail];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/8000M15  SIP/2.0 200 OK     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK544     From: <sip:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>;tag=1926     Call-ID: 526272332146783569054     CSeq: 43252 INVITE     Contact: <sip:[e-mail]>     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/8000M16  ConnectM17  ConnectM18  TerminalCapabilitySetM19  TerminalCapabilitySetM20  TerminalCapabilitySetAckM21  TerminalCapabilitySetAckM22  TerminalCapabilitySetM23  TerminalCapabilitySetM24  TerminalCapabilitySetAckM25  TerminalCapabilitySetAckM26  MasterSlaveDeterminationM27  MasterSlaveDeterminationM28  MasterSlaveDeterminationAckM29  MasterSlaveDeterminationAckM30  OpenLogicalChannel     g711uLaw 1.28.18.57 60002M31  OpenLogicalChannel     g711uLaw 1.28.18.57 60002M32  OpenLogicalChannelAckM33  OpenLogicalChannelAck     Call Flow Examples 181M34  OpenLogicalChannel     g711uLaw 4.30.19.04 5004M35  OpenLogicalChannel     g711uLaw 4.30.19.04 5004M36  OpenLogicalChannelAckM37  OpenLogicalChannelAckM38  ACK sip:[e-mail] SIP/2.0     Via: SIP/2.0/TCP 2.3.4.5:4344;branch=z9hG4bK32     Max-Forwards: 70     From: <sip:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>;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/8000M39  ACK sip:[e-mail] 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:[e-mail]>;tag=3q526g45     To: <sip:[e-mail]>;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