图4-10是软交换之间的呼叫流程。
下面是软交换之间SIP消息的格式：
♦ INVITE
消息如下：
INVITE sip:66500002@191.169.1.116:5060;User=phone
SIP/2.0
Allow:INVITE,ACK,BYE,CANCEL,PRACK...；允许
From:<sip:7670000@191J694J12:5061;UseP=phone>;tag=446B5358336B534H)00()9820；发端
To:<sip:66500002@191.169.1.116:5060;User=phone>；收端
Supported: lOOrel
Content-Type:multipart/mixed;boundary=unique-boundary-1；内容
Call-ID:01F01A709DA1400000000001@191.169.1.112；呼叫 ID
CSeq:l INVITE
Expires:180；过期时间
Via:SIP/2.0/UDP 191.169.1.112:5061; branch^
Record-Route: <sip: 191.169.1.112;lr>
Contact:<sip:7670000@191.169.1.112:5061>
Max-Forwards:70；最大转发次数
Content-Length:597 ；内容长度
-unique-boundary-1
Content-Type:application/SDP
v=0
o=SoftX 1073741827 1073741827 IN IP4 191.169.1.112 s=Sip Call
c=IN IP4 191.169.1.45；连接
t=0 0
m=audio 14380 RTP/AVP 804 18；媒体类型 a=rtpmap:8 PCMA/8000 a=rtpmap:0 PCMU/8000 a=rtpmap:4 G723/8000 a=rtpmap:18 G729/8000
—unique-boundary-1
Content-Type:application/ISUP; version=；itu-t92+;base= itu-t92+
Content-Disposition: signal; handling=optional
01 00 20 00 0A 03 02 09 07 83 90 66 05 00 20 OF 08 01 00 0A 06 81 13 67 07 00 00 00
-unique-boundary-1—
♦ SIP/2.0 100 Trying
消息如下：
Call-ID:01F01A709DA1400000000001@191.169.1.112
CSeq:l INVITE
Fmm:<sip:7670000@191.169丄112:5061;Useuphoiie>;ta沪446B5358336B534F00009820；发端
To:<sip:66500002@191.169.1.116:5060;User=phone>；收端
Via:SIP/2.0/UDP 191.169.1.112:5061;branch=
Content-Length:0
♦ SIP/2.0 180 Ringing
消息如下：
Allow:INVITE,ACK,BYE,CANCEL,PRACK
Require: lOOrel
Supported: lOOrel
Via:SIP/2.0/UDP 191.169.1.112:5061
Call-ID:01F01A709DA1400000000001@191.169.1.112
CSeq:l INVITE
Fiom:<sip:7670000@ 191.169 丄 112:5061;Useuphone>;tag=446B5358336B534F00009820「发端 To:<sip:66500002@191.169.1.116:5060;Usen=phone>;tag=5358336B534F7A5F0021649B；收端
RSeq:633013647
Contact:<sip:66500002@191.169.1.116:5061>
Content-Length:4:内容长度
Content-Type:application/ISUP
06 C2 00 00
180中任选包含SDP信息
.PRACK
消息如下：
PRACK sip:66500002@191.169.1.116:5060;User=phone SIP/2.0
Call-ID:01F01A709DA1400000000001@191.169.1.112
CSeq:2 PRACK
From:<sip:767(XW@191.169.1.112:5()61;Usen=phone>;tag=446B5358336B534HX)0()9820；发端
To:<sip:66500002@ 191.169.1.116:5060;Usen=phone>;tag=5358336B534F7A5H)021649B ；收端
RAck:633013647 1 INVITE
Vh：SIP/2.0/UDP
191.169.1.112:5061;branch=898E03EElDBA24C581E03DB69E23FF0L80000001
Max-Forwards:70；最大转发次数
Content-Length:0 ；长度
♦ SIP/2.0 200 OK
消息如下：
Call-ID:01F01A709DA1400000000001@191.169.1.112
CSeq:2 PRACK
FK)m:<sip:7670000@191.169.1.112:5061;UseF=phoiie>;tag=446B5358336B534F00009820；发端 Tb:<sip:66500002@191.169.1.116:5060;Usen=phone>;tag=5358336B534F7A5F0021649B;收端 Via:SIP/2.0/UDP
191.169.1.112:5061;branch=898E03EElDBA24C581E03DB69E23FF01.80000001
Content-Length:0 ；内容长度
♦ SIP/2.0 200 OK
消息如下：
Content-Type:multipart/inixed;boundary=unique-boundary-l
Via:SIP/2.0/UDP 191.169.1.112:5061
Call-ID:01F01A709DA1400000000001@191.169.1.112；呼叫 ID
CSeq:l INVITE
From:<sip:7670000@191.169丄 112:5061;Usen=phog>;tag=446B5358336B534F00009820；发端
Ib:<sip:66500002@191.169.1.116:5060;Us^phone>;tag=5358336B534F7A5F0021649B；收端
Contact:<sip:66500002@191.169.1.116:5061>
Content-Length:298 ；长度
-unique-boundary-1
Content-Type:application/SDP；内容类型
v=0
o=SS 1073741851 1073741851 INIP4 191.169.1.116
s=Sip Call
c=IN IP4 191.169.1.35；连接
t=0 0
m=audio 30000 RTP/AVP & 媒体类型
a=rtpmap:8 PCMA/8000
-unique-boundary-1
Content-Type:application/ISUP; version=itu-t92+;base= itu-t92+
Content-Disposition: signal; handling=optional
09 01 1103C6 00 00 00
-unique-boundary-1—
♦ ACK sip:66500002@ 191.169.1.116:5061 SIP/2.0
消息如下：
Call-ID:01F01A709DA1400000000001@191.169.1.112；呼叫 ID
CSeq:l ACK
From:<sip:7670000@191.169.1.112:5061;User=Thone>;tag=446B5358336B534F00009820；发端
To:<sip:66500002@ 191.169.1.116:5060;UseF=phone>;tag=5358336B534F7A5F0021649B ；收端
Via:SIP/2,0/UDP 191.169.1.112:5061
Max-Forwards:70；最大转发次数
Content-Length:0 ；长度
♦ BYE
消息如下：
BYE sip:7670000@191.169.1.112:5061 SIP/2.0 Call-ID:01F01A709DA1400000000001@191.169.1.112；呼叫 ID
CSeq:l BYE
Fronr<^p:66500002@191169JJ16:5060;Usec=[tone>;tag=5358336B534F7A5H)021649B；发端 Tb:<sip:7670000@191.169.1.112:5061;Usen=phone>;tag=446B5358336B534F00009820；收端 Via:SIP/2,0/UDP 191.169.1.116:5061
Max-Forwards:70；最大转发次数
Content-Length:6
Content-Type:application/ISUP; version=itu-t92+;base= itu-t92+；内容类型
Content-Disposition: signal; handling=optional
0c0102 65 9f00
BYE中应该封装Rel的信息，接收方如果在接收到不封装Rel的BYE时应该正常地接收 •处理。
♦ SIP/2.0 200 0K
消息如下：
Via:SIP/2.0/UDP 191.169.1.116:5061
Call-ID:01F01A709DA1400000000001@191.169.1.112；呼叫 ID
CSeq:l BYE
Fn>m:<sip:66500002@191.169.1.U6:5060;User=phone>;tag=5358336B534F7A5F0021649B；发端 To:<sip:7670000@ 191.169.1.U2:5061;User^phone>;tag=446B5358336B534F00009820；收端 Content-Lengthr。
