三方通话（二）

话机上三方通话建立过程如下消息：

(1) 用户3315呼叫用户3305，终端发送INVITE消息给IPBX.

INVITE sip:3305@192.168.50.244 SIP/2.0
Via: SIP/2.0/UDP 192.168.50.119:31682;branch=z9hG4bK1791327125;rport
From: "3315" <sip:3315@192.168.50.244>;tag=107903851
To: <sip:3305@192.168.50.244>
Call-ID: 1436543274-31682-8@BJC.BGI.FA.BBJ
CSeq: 71 INVITE
Contact: "3315" <sip:3315@192.168.50.119:31682>
Max-Forwards: 70
Allow: INVITE, ACK, OPTIONS, CANCEL, BYE, SUBSCRIBE, NOTIFY, INFO, REFER, UPDATE, MESSAGE
Content-Type: application/sdp
Content-Length:   679


v=0
o=3315 8000 8000 IN IP4 192.168.50.119
s=SIP Call
c=IN IP4 192.168.50.119
t=0 0
m=audio 18610 RTP/AVP 0 8 4 18 9 3 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:4 G723/8000
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:9 G722/8000
a=rtpmap:3 GSM/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
m=video 12756 RTP/AVP 99 34 100
a=rtpmap:99 H264/90000
a=fmtp:99 profile-level-id=428014; packetization-mode=0; sprop-parameter-sets=Z0KADJWgUH5A,aM4Ecg==; max-br=128
a=rtpmap:34 H263/90000
a=fmtp:34 CIF=1; QCIF=1; MaxBR=1280
a=rtpmap:100 H263-1998/90000
a=fmtp:100 CIF=1; QCIF=1; MaxBR=1280




(2) IPBX向终端3315发送”100 Trying“消息。IPBX告诉终端说，我收到INVITE消息，你停止重发INVITE请求定时器。


SIP/2.0 100 Trying
Via: SIP/2.0/UDP 192.168.50.119:31682;branch=z9hG4bK1791327125;rport
From: "3315" <sip:3315@192.168.50.244>;tag=107903851
To: <sip:3305@192.168.50.244>;tag=6efc4ba34
Call-ID: 1436543274-31682-8@BJC.BGI.FA.BBJ
CSeq: 71 INVITE
Contact: <sip:3305@192.168.50.244:5060>
Content-Length: 0


(3) IPBX对收到的INVITE请求消息进行分析，查找到用户3305存在，发送INVITE请求到终端3305.


INVITE sip:3305@192.168.50.93 SIP/2.0
Via: SIP/2.0/UDP 192.168.50.244:5060;branch=30d7674e
From: "3315" <sip:3315@192.168.50.244>;tag=0e0e8bc3
Contact: <sip:3315@192.168.50.244:5060>
To: <sip:3305@192.168.50.93>
Call-ID: 143262982667db0e5807e7772567dcbc61@f432a8c0
CSeq: 56416 INVITE
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 723


v=0
o=root 819423054 819423054 IN IP4 192.168.50.244
s=session
c=IN IP4 192.168.50.244
t=0 0
m=audio 18012 RTP/AVP 0 8 4 18 3 114 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:4 G723/8000
a=rtpmap:18 G729/8000
a=rtpmap:3 GSM/8000
a=rtpmap:114 AMR/8000
a=fmtp:114 octet-align=1;mode-set=7,0
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
m=video 46042 RTP/AVP 99 34 100 98
a=rtpmap:99 H264/90000
a=fmtp:99 profile-level-id=428014; packetization-mode=0; sprop-parameter-sets=Z0KADJWgUH5A,aM4Ecg==; max-br=128
a=rtpmap:34 H263/90000
a=fmtp:34 CIF=1; QCIF=1; MaxBR=1280
a=rtpmap:100 H263-1998/90000
a=fmtp:100 CIF=1; QCIF=1; MaxBR=1280
a=rtpmap:98 MP4V-ES/90000
a=fmtp:98 profile-level-id=3


(4) 终端收到IPBX发送的请求消息，并且向IPBX发送”100 Trying“消息。告诉IPBX说，我收到INVITE消息，你停止重发INVITE请求定时器。


SIP/2.0 100 Trying
Via: SIP/2.0/UDP 192.168.50.244:5060;branch=30d7674e
From: "3315" <sip:3315@192.168.50.244>;tag=0e0e8bc3
To: <sip:3305@192.168.50.93>;tag=1349096325
Call-ID: 143262982667db0e5807e7772567dcbc61@f432a8c0
CSeq: 56416 INVITE
Contact: <sip:3305@192.168.50.93:5060>
Content-Length: 0


(5) 终端响铃，并且告诉IPBX。


SIP/2.0 180 Ringing
Via: SIP/2.0/UDP 192.168.50.244:5060;branch=30d7674e
From: "3315" <sip:3315@192.168.50.244>;tag=0e0e8bc3
To: <sip:3305@192.168.50.93>;tag=1349096325
Call-ID: 143262982667db0e5807e7772567dcbc61@f432a8c0
CSeq: 56416 INVITE
Contact: <sip:3305@192.168.50.93:5060>
Content-Length: 0


(6) IPBX告诉终端，被叫用户3305正在响铃。


SIP/2.0 1