1. 概述

本文通过tcpdump对真实环境里的软电话的注册、呼叫、挂断流程进行抓包，通过真实的例子学习SIP协议。本文主要包括以下方面:

A. 详解软电话的注册时的SIP包和流程图
B. 详解软电话之间呼叫、挂断的SIP包和流程图
C. 详细介绍了协议中各个字段的意义

2. 案例环境说明

软电话使用x-lite，使用freeswitch的默认的两个号码1008和1018。

freeswitch部署在服务器的私网地址是172.23.4.92，公网地址115.aa.aa.aa。
1008的测试机器在私网上（IP为10.240.80.69），通过115.aa.aa.aa:5060注册freeswitch，但是出去后的公网地址是59.bb.bb.bb。
1018的测试机器在私网上，通过115.aa.aa.aa:5060注册freeswitch,但是出去后的公网地址是123.cc.cc.cc

在172.23.4.92上，使用tcpdump捕获通信过程中的所有包为了安全，本文把真实环境的公网地址，全部使用假的地址进行替换

3. SIP注册流程

1008 向115.aa.aa.aa:5060 进行注册

3.1. 注册流程图

下文的流程图如下：
这里写图片描述

3.2. SIP注册交互过程协议

A. 1008 向freeswitch第一次发起注册

No.     Time           Source                Destination           Protocol Length Info
    201 8.599836       10.240.80.69          115.aa.aa.aa      SIP      599    Request: REGISTER sip:115.aa.aa.aa:5060  (1 binding) | 

Frame 201: 599 bytes on wire (4792 bits), 599 bytes captured (4792 bits) on interface 0
Ethernet II, Src: Giga-Byt_bf:ae:ce (40:8d:5c:bf:ae:ce), Dst: CiscoInc_53:c8:c2 (e8:65:49:53:c8:c2)
Internet Protocol Version 4, Src: 10.240.80.69, Dst: 115.aa.aa.aa
User Datagram Protocol, Src Port: 59531 (59531), Dst Port: 5060 (5060)
Session Initiation Protocol (REGISTER)
    Request-Line: REGISTER sip:115.aa.aa.aa:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59531;branch=z9hG4bK-524287-1---671b073f870cfe63;rport
        Max-Forwards: 70
        Contact: <sip:1008@10.240.80.69:59531;rinstance=b22023be9ce02608>
        To: "1008"<sip:1008@115.aa.aa.aa:5060>
        From: "1008"<sip:1008@115.aa.aa.aa:5060>;tag=9a71ed3c
        Call-ID: 84253M2Q3MDQyZDY0Y2I2NTg1MGE3ZTExODQ0ODIyNDNkYTE
        CSeq: 1 REGISTER
        Expires: 3600
        Allow: SUBSCRIBE, NOTIFY, INVITE, ACK, CANCEL, BYE, REFER, INFO, OPTIONS, MESSAGE
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Content-Length: 0

协议中字段的说明：
这里写图片描述

B. freeswitch返回 401 未认证消息
freeswitch在返回sip消息中新增参数：

认证摘要WWW-Authenticate给客户端
CSeq序号变成1

No.     Time           Source                Destination           Protocol Length Info
    202 8.604062       115.aa.aa.aa      10.240.80.69          SIP      727    Status: 401 Unauthorized | 

Frame 202: 727 bytes on wire (5816 bits), 727 bytes captured (5816 bits) on interface 0
Ethernet II, Src: CiscoInc_53:c8:c2 (e8:65:49:53:c8:c2), Dst: Giga-Byt_bf:ae:ce (40:8d:5c:bf:ae:ce)
Internet Protocol Version 4, Src: 115.aa.aa.aa, Dst: 10.240.80.69
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 59531 (59531)
Session Initiation Protocol (401)
    Status-Line: SIP/2.0 401 Unauthorized
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59531;branch=z9hG4bK-524287-1---671b073f870cfe63;rport=35646;received=59.bb.bb.bb
        From: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=9a71ed3c
        To: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=va161eH7mmgNc
        Call-ID: 84253M2Q3MDQyZDY0Y2I2NTg1MGE3ZTExODQ0ODIyNDNkYTE
        CSeq: 1 REGISTER
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        WWW-Authenticate: Digest realm="115.aa.aa.aa", nonce="1118e141-6f6d-4cee-a7d7-5061f8d8a2da", algorithm=MD5, qop="auth"
        Content-Length: 0

C. 1008第二次发起注册请求
1008收到401未认证消息，会重新发起注册请求，并加上根据收到的认证摘要和1008的用户名密码生成的认证消息（Authorization头）。另外CSeq序号变成2

No.     Time           Source                Destination           Protocol Length Info
    203 8.606034       10.240.80.69          115.aa.aa.aa      SIP      859    Request: REGISTER sip:115.aa.aa.aa:5060  (1 binding) | 

Frame 203: 859 bytes on wire (6872 bits), 859 bytes captured (6872 bits) on interface 0
Ethernet II, Src: Giga-Byt_bf:ae:ce (40:8d:5c:bf:ae:ce), Dst: CiscoInc_53:c8:c2 (e8:65:49:53:c8:c2)
Internet Protocol Version 4, Src: 10.240.80.69, Dst: 115.aa.aa.aa
User Datagram Protocol, Src Port: 59531 (59531), Dst Port: 5060 (5060)
Session Initiation Protocol (REGISTER)
    Request-Line: REGISTER sip:115.aa.aa.aa:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59531;branch=z9hG4bK-524287-1---726c884045c07c61;rport
        Max-Forwards: 70
        Contact: <sip:1008@10.240.80.69:59531;rinstance=b22023be9ce02608>
        To: "1008"<sip:1008@115.aa.aa.aa:5060>
        From: "1008"<sip:1008@115.aa.aa.aa:5060>;tag=9a71ed3c
        Call-ID: 84253M2Q3MDQyZDY0Y2I2NTg1MGE3ZTExODQ0ODIyNDNkYTE
        CSeq: 2 REGISTER
        Expires: 3600
        Allow: SUBSCRIBE, NOTIFY, INVITE, ACK, CANCEL, BYE, REFER, INFO, OPTIONS, MESSAGE
        User-Agent: X-Lite release 4.9.8 stamp 84253
         [truncated]Authorization: Digest username="1008",realm="115.aa.aa.aa",nonce="1118e141-6f6d-4cee-a7d7-5061f8d8a2da",uri="sip:115.aa.aa.aa:5060",response="1cd1bea82808566209948ba2eb53c9f1",cnonce="7761e8692660d5ee8467fc4a3974afe3",nc=
        Content-Length: 0

D. Freeswitch注册成功返回200
Freeswitch收到请求后，对请求进行核实，如果认证通过，则返回200 OK消息。此时1008在freeswitch注册成功。freeswitch会将1008在SIP消息中的联系地址（contact字段）记录下来。如果有人呼叫1008，则freeswitch会向该地址发送SIP消息建立呼叫

补充，如果认证失败，则返回403 Forbidden消息

No.     Time           Source                Destination           Protocol Length Info
    204 8.611684       115.aa.aa.aa      10.240.80.69          SIP      711    Status: 200 OK  (1 binding) | 

Frame 204: 711 bytes on wire (5688 bits), 711 bytes captured (5688 bits) on interface 0
Ethernet II, Src: CiscoInc_53:c8:c2 (e8:65:49:53:c8:c2), Dst: Giga-Byt_bf:ae:ce (40:8d:5c:bf:ae:ce)
Internet Protocol Version 4, Src: 115.aa.aa.aa, Dst: 10.240.80.69
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 59531 (59531)
Session Initiation Protocol (200)
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59531;branch=z9hG4bK-524287-1---726c884045c07c61;rport=35646;received=59.bb.bb.bb
        From: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=9a71ed3c
        To: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=XKtZ391ajX67Q
        Call-ID: 84253M2Q3MDQyZDY0Y2I2NTg1MGE3ZTExODQ0ODIyNDNkYTE
        CSeq: 2 REGISTER
        Contact: <sip:1008@10.240.80.69:59531;rinstance=b22023be9ce02608>;expires=3600
        Date: Wed, 25 Oct 2017 08:26:48 GMT
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        Content-Length: 0

4. SIP呼叫流程

1008 呼叫 1018，然后接通通话，最后1018挂断电话

4.1. 呼叫、挂断流程图

下文的流程图如下：

这里写图片描述

下方的SIP协议中，都包含SDP协议，这里的SDP用于1008和1018软电话对通话参数协商，使用通话双方能够通过RTP进行通信。本文我不介绍SDP内容。

4.2. SIP呼叫交互过程协议

A. 1008 向freeswitch发起INVITE 消息，请求建立一个呼叫

No.     Time           Source                Destination           Protocol Length Info
    267 15.676245      59.bb.bb.bb         172.23.4.92           SIP/SDP  968    Request: INVITE sip:1018@115.aa.aa.aa:5060 | 

Frame 267: 968 bytes on wire (7744 bits), 968 bytes captured (7744 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 59.bb.bb.bb, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 24576 (24576), Dst Port: 5060 (5060)
Session Initiation Protocol (INVITE)
    Request-Line: INVITE sip:1018@115.aa.aa.aa:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59535;branch=z9hG4bK-524287-1---eafafc5cc50b9a41;rport
        Max-Forwards: 70
        Contact: <sip:1008@59.bb.bb.bb:24576;rinstance=9d87a2b91a59c5b9>
        To: <sip:1018@115.aa.aa.aa:5060>
        From: "1008"<sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 1 INVITE
        Allow: SUBSCRIBE, NOTIFY, INVITE, ACK, CANCEL, BYE, REFER, INFO, OPTIONS, MESSAGE
        Content-Type: application/sdp
        Supported: replaces
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Content-Length: 334
    Message Body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): - 13153395802875591 1 IN IP4 10.240.80.69
            Session Name (s): X-Lite release 4.9.8 stamp 84253
            Connection Information (c): IN IP4 10.240.80.69
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 64836 RTP/AVP 9 8 120 0 84 101
            Media Attribute (a): rtpmap:120 opus/48000/2
            Media Attribute (a): fmtp:120 useinbandfec=1; usedtx=1; maxaveragebitrate=64000
            Media Attribute (a): rtpmap:84 speex/16000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-15
            Media Attribute (a): sendrecv

B freeswitch 回送 100 trying
freeswitch通过100 trying消息通知1008已经收到他的请求。对1008的权限进行验证，如果通过，则此时1008的UA和freeswitch的UA通信通道已经建立，被称之为freeswitch的一条腿，又称a-leg

No.     Time           Source                Destination           Protocol Length Info
    268 15.676821      172.23.4.92           59.bb.bb.bb         SIP      427    Status: 100 Trying | 

Frame 268: 427 bytes on wire (3416 bits), 427 bytes captured (3416 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 59.bb.bb.bb
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 24576 (24576)
Session Initiation Protocol (100)
    Status-Line: SIP/2.0 100 Trying
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59535;branch=z9hG4bK-524287-1---eafafc5cc50b9a41;rport=24576;received=59.bb.bb.bb
        From: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        To: <sip:1018@115.aa.aa.aa:5060>
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 1 INVITE
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Content-Length: 0

C. freeswitch向1018发送INVITE信息
freeswitch进行路由找到1018的信息，向1018发送INVITE信息。
重要参数

1.Remote-Party-ID：实现主叫的显号功能，即1018的客户端显示的来电号码

No.     Time           Source                Destination           Protocol Length Info
    508 25.731551      172.23.4.92           123.cc.cc.cc       SIP/SDP  1361   Request: INVITE sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600 | 

Frame 508: 1361 bytes on wire (10888 bits), 1361 bytes captured (10888 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 123.58.160.154
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 36841 (36841)
Session Initiation Protocol (INVITE)
    Request-Line: INVITE sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport;branch=z9hG4bK85Z552j3KHv4K
        Route: <sip:1018@123.58.160.154:36841>;rinstance=0d9373ba78a06600
        Max-Forwards: 68
        From: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        To: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 114125036 INVITE
        Contact: <sip:mod_sofia@115.aa.aa.aa:5060>
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        Allow-Events: talk, hold, conference, presence, as-feature-event, dialog, line-seize, call-info, sla, include-session-description, presence.winfo, message-summary, refer
        Content-Type: application/sdp
        Content-Disposition: session
        Content-Length: 274
        X-FS-Support: update_display,send_info
        Remote-Party-ID: "1008" <sip:1008@172.23.4.92>;party=calling;screen=yes;privacy=off
    Message Body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): FreeSWITCH 1508895355 1508895356 IN IP4 115.aa.aa.aa
            Session Name (s): FreeSWITCH
            Connection Information (c): IN IP4 115.aa.aa.aa
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 26828 RTP/AVP 9 8 0 101
            Media Attribute (a): rtpmap:9 G722/8000
            Media Attribute (a): rtpmap:8 PCMA/8000
            Media Attribute (a): rtpmap:0 PCMU/8000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-16
            Media Attribute (a): ptime:20

D. 1018 回送100 trying

1018 回送100 trying 消息通知freeswitch，它已经正常接收到INVITE消息，正在准备进行下一步处理

No.     Time           Source                Destination           Protocol Length Info
    513 25.824373      123.cc.cc.cc       172.23.4.92           SIP      346    Status: 100 Trying | 

Frame 513: 346 bytes on wire (2768 bits), 346 bytes captured (2768 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 123.58.160.154, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 36841 (36841), Dst Port: 5060 (5060)
Session Initiation Protocol (100)
    Status-Line: SIP/2.0 100 Trying
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport=5060;branch=z9hG4bK85Z552j3KHv4K
        To: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>
        From: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 114125036 INVITE
        Content-Length: 0

E. 1018 回送180 ring 消息
1018 进行振铃，并向freeswitch回送180 ring消息，通知1018正在振铃

No.     Time           Source                Destination           Protocol Length Info
    520 26.377340      123.cc.cc.cc       172.23.4.92           SIP      507    Status: 180 Ringing | 

Frame 520: 507 bytes on wire (4056 bits), 507 bytes captured (4056 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 123.58.160.154, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 36841 (36841), Dst Port: 5060 (5060)
Session Initiation Protocol (180)
    Status-Line: SIP/2.0 180 Ringing
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport=5060;branch=z9hG4bK85Z552j3KHv4K
        Contact: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>
        To: "1018"<sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>;tag=e243b65d
        From: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 114125036 INVITE
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Allow-Events: talk, hold
        Content-Length: 0

F. freeswitch 给 1008 发送 183 消息
freeswitch 向1008产生一个回铃音，通过RTP发送给1008

No.     Time           Source                Destination           Protocol Length Info
    525 26.399001      172.23.4.92           59.bb.bb.bb         SIP/SDP  1228   Status: 183 Session Progress | 

Frame 525: 1228 bytes on wire (9824 bits), 1228 bytes captured (9824 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 59.bb.bb.bb
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 24576 (24576)
Session Initiation Protocol (183)
    Status-Line: SIP/2.0 183 Session Progress
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59535;branch=z9hG4bK-524287-1---eafafc5cc50b9a41;rport=24576;received=59.bb.bb.bb
        From: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        To: <sip:1018@115.aa.aa.aa:5060>;tag=6813p45D61j9a
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 1 INVITE
        Contact: <sip:1018@115.aa.aa.aa:5060;transport=udp>
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Accept: application/sdp
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        Allow-Events: talk, hold, conference, presence, as-feature-event, dialog, line-seize, call-info, sla, include-session-description, presence.winfo, message-summary, refer
        Content-Type: application/sdp
        Content-Disposition: session
        Content-Length: 226
        Remote-Party-ID: "1018" <sip:1018@115.aa.aa.aa>;party=calling;privacy=off;screen=no
    Message Body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): FreeSWITCH 1508899003 1508899004 IN IP4 115.aa.aa.aa
            Session Name (s): FreeSWITCH
            Connection Information (c): IN IP4 115.aa.aa.aa
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 23180 RTP/AVP 9 101
            Media Attribute (a): rtpmap:9 G722/8000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-16
            Media Attribute (a): ptime:20

G. 1018 回送200 OK
1018 接听电话，向freeswitch回送200 OK消息

No.     Time           Source                Destination           Protocol Length Info
    741 27.795404      123.cc.cc.cc       172.23.4.92           SIP/SDP  815    Status: 200 OK | 

Frame 741: 815 bytes on wire (6520 bits), 815 bytes captured (6520 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 123.58.160.154, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 36841 (36841), Dst Port: 5060 (5060)
Session Initiation Protocol (200)
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport=5060;branch=z9hG4bK85Z552j3KHv4K
        Contact: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>
        To: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>;tag=e243b65d
        From: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 114125036 INVITE
        Allow: SUBSCRIBE, NOTIFY, INVITE, ACK, CANCEL, BYE, REFER, INFO, OPTIONS, MESSAGE
        Content-Type: application/sdp
        Supported: replaces
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Content-Length: 208
    Message Body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): - 2353942294 3 IN IP4 10.240.80.146
            Session Name (s): X-Lite release 4.9.8 stamp 84253
            Connection Information (c): IN IP4 10.240.80.146
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 59974 RTP/AVP 9 8 0 101
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-15
            Media Attribute (a): sendrecv

H. freeswitch向1018回送ACK证实消息
freeswitch向1018回送ACK证实消息，确认已经收到请求。此时 freeswitch和1018的通知通道已经建立，称为b-leg

No.     Time           Source                Destination           Protocol Length Info
    742 27.798013      172.23.4.92           123.cc.cc.cc       SIP      466    Request: ACK sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600 | 

Frame 742: 466 bytes on wire (3728 bits), 466 bytes captured (3728 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 123.58.160.154
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 36841 (36841)
Session Initiation Protocol (ACK)
    Request-Line: ACK sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport;branch=z9hG4bK9eSy7X36gtjQF
        Max-Forwards: 70
        From: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        To: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>;tag=e243b65d
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 114125036 ACK
        Contact: <sip:mod_sofia@115.aa.aa.aa:5060>
        Content-Length: 0

I. freeswitch 向1008发送200K消息
freeswitch向1008发送200K消息，并切断原先自动产生的回铃音，将1018的接进来

No.     Time           Source                Destination           Protocol Length Info
    788 27.816687      172.23.4.92           59.bb.bb.bb         SIP/SDP  1234   Status: 200 OK | 

Frame 788: 1234 bytes on wire (9872 bits), 1234 bytes captured (9872 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 59.bb.bb.bb
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 24576 (24576)
Session Initiation Protocol (200)
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59535;branch=z9hG4bK-524287-1---eafafc5cc50b9a41;rport=24576;received=59.bb.bb.bb
        From: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        To: <sip:1018@115.aa.aa.aa:5060>;tag=6813p45D61j9a
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 1 INVITE
        Contact: <sip:1018@115.aa.aa.aa:5060;transport=udp>
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        Allow-Events: talk, hold, conference, presence, as-feature-event, dialog, line-seize, call-info, sla, include-session-description, presence.winfo, message-summary, refer
        Session-Expires: 120;refresher=uas
        Content-Type: application/sdp
        Content-Disposition: session
        Content-Length: 226
        Remote-Party-ID: "Outbound Call" <sip:1018@115.aa.aa.aa>;party=calling;privacy=off;screen=no
    Message Body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): FreeSWITCH 1508899003 1508899004 IN IP4 115.aa.aa.aa
            Session Name (s): FreeSWITCH
            Connection Information (c): IN IP4 115.aa.aa.aa
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 23180 RTP/AVP 9 101
            Media Attribute (a): rtpmap:9 G722/8000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-16
            Media Attribute (a): ptime:20

J. 1008回送freeswitch ACK消息
1008回送freeswitch ACK消息，他已经收到200消息
此时a-leg和b-leg的通话建立完毕，freeswitch将两个leg桥接起来，使得双方可以正常通话

No.     Time           Source                Destination           Protocol Length Info
    792 27.827819      59.bb.bb.bb         172.23.4.92           SIP      524    Request: ACK sip:1018@115.aa.aa.aa:5060;transport=udp | 

Frame 792: 524 bytes on wire (4192 bits), 524 bytes captured (4192 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 59.bb.bb.bb, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 24576 (24576), Dst Port: 5060 (5060)
Session Initiation Protocol (ACK)
    Request-Line: ACK sip:1018@115.aa.aa.aa:5060;transport=udp SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.240.80.69:59535;branch=z9hG4bK-524287-1---aa9f7e058653c625;rport
        Max-Forwards: 70
        Contact: <sip:1008@59.bb.bb.bb:24576;rinstance=9d87a2b91a59c5b9>
        To: <sip:1018@115.aa.aa.aa:5060>;tag=6813p45D61j9a
        From: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 1 ACK
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Content-Length: 0

4.3. SIP挂断电话交互过程协议

A. 1018 挂断电话，向freeswitch发送BYE消息
1018 挂断电话，向freeswitch发送BYE消息，freeswitch进行拆线

No.     Time           Source                Destination           Protocol Length Info
   1826 32.660666      123.cc.cc.cc       172.23.4.92           SIP      523    Request: BYE sip:mod_sofia@115.aa.aa.aa:5060 | 

Frame 1826: 523 bytes on wire (4184 bits), 523 bytes captured (4184 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 123.58.160.154, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 36841 (36841), Dst Port: 5060 (5060)
Session Initiation Protocol (BYE)
    Request-Line: BYE sip:mod_sofia@115.aa.aa.aa:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.240.80.146:49713;branch=z9hG4bK-524287-1---e2a3f037aa702259;rport
        Max-Forwards: 70
        Contact: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>
        To: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        From: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>;tag=e243b65d
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 2 BYE
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Content-Length: 0

B. freeswitch回送200消息
freeswitch回送200消息，并释放b-leg

No.     Time           Source                Destination           Protocol Length Info
   1829 32.682037      172.23.4.92           123.cc.cc.cc       SIP      590    Status: 200 OK | 

Frame 1829: 590 bytes on wire (4720 bits), 590 bytes captured (4720 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 123.58.160.154
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 36841 (36841)
Session Initiation Protocol (200)
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 10.240.80.146:49713;branch=z9hG4bK-524287-1---e2a3f037aa702259;rport=36841;received=123.58.160.154
        From: <sip:1018@123.58.160.154:36841;rinstance=0d9373ba78a06600>;tag=e243b65d
        To: "1008" <sip:1008@172.23.4.92>;tag=7HUvrZpH3a9Up
        Call-ID: 30b8d974-3406-1236-52a1-00505683024d
        CSeq: 2 BYE
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        Content-Length: 0

C. freeswitch向1008发送BYE消息

freeswitch向1008发送BYE消息，通知1008拆线重要参数

1.Reason：说明挂断的原因

No.     Time           Source                Destination           Protocol Length Info
   1858 32.698972      172.23.4.92           59.bb.bb.bb         SIP      661    Request: BYE sip:1008@59.bb.bb.bb:24576;rinstance=9d87a2b91a59c5b9 | 

Frame 1858: 661 bytes on wire (5288 bits), 661 bytes captured (5288 bits)
Ethernet II, Src: Vmware_83:02:4d (00:50:56:83:02:4d), Dst: IETF-VRRP-VRID_04 (00:00:5e:00:01:04)
Internet Protocol Version 4, Src: 172.23.4.92, Dst: 59.bb.bb.bb
User Datagram Protocol, Src Port: 5060 (5060), Dst Port: 24576 (24576)
Session Initiation Protocol (BYE)
    Request-Line: BYE sip:1008@59.bb.bb.bb:24576;rinstance=9d87a2b91a59c5b9 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport;branch=z9hG4bKarjQ9rmae389a
        Max-Forwards: 70
        From: <sip:1018@115.aa.aa.aa:5060>;tag=6813p45D61j9a
        To: "1008" <sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 114125039 BYE
        User-Agent: FreeSWITCH-mod_sofia/1.6.19-36-7a77e0b~64bit
        Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
        Supported: timer, path, replaces
        Reason: Q.850;cause=16;text="NORMAL_CLEARING"
        Content-Length: 0

D. 1008回送200消息
1008回送200消息, freeswitch收到后，也释放a-leg，通话结束

No.     Time           Source                Destination           Protocol Length Info
   1879 32.818814      59.bb.bb.bb         172.23.4.92           SIP      459    Status: 200 OK | 

Frame 1879: 459 bytes on wire (3672 bits), 459 bytes captured (3672 bits)
Ethernet II, Src: ZteCorpo_60:22:21 (00:22:93:60:22:21), Dst: Vmware_83:02:4d (00:50:56:83:02:4d)
Internet Protocol Version 4, Src: 59.bb.bb.bb, Dst: 172.23.4.92
User Datagram Protocol, Src Port: 24576 (24576), Dst Port: 5060 (5060)
Session Initiation Protocol (200)
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 115.aa.aa.aa;rport=5060;branch=z9hG4bKarjQ9rmae389a
        Contact: <sip:1008@59.bb.bb.bb:24576;rinstance=9d87a2b91a59c5b9>
        To: "1008"<sip:1008@115.aa.aa.aa:5060>;tag=54bd8d3a
        From: <sip:1018@115.aa.aa.aa:5060>;tag=6813p45D61j9a
        Call-ID: 84253MGY3OGQwZWI1OGQ3YTRlZTYwZjQ3ZDZjZDhjNDNiMTU
        CSeq: 114125039 BYE
        User-Agent: X-Lite release 4.9.8 stamp 84253
        Content-Length: 0

参考文献

本文中的所有的图，都是作者用手机拍摄自图书”freeswitch权威指南”