sip协议(rfc2361)要点笔记(一)

sip协议(rfc2361)原文

sip协议原文:rfc2361

旧版sip协议原文:rfc2543

基础要点

request line的格式为：

Method SP Request-URI SP SIP-Version CRLF

SP 是空格，Request-URI 是请求的资源，SIP-Version 是sip协议版本号，CRLF 是回车换行。信令主要有：REGISTER,INVITE,ACK,CANCEL,BYE,OPTIONS,INFO,SUBSCRIBE,NOTIFY,REFER,MESSAGE

uri完整格式:

sip:user:password@host:port;uri-parameters?headers

response line的格式为：

SIP-Version SP Status-Code SP Reason-Phrase CRLF

SIP-Version 是sip协议版本号，Status-Code 是响应码，Reason-Phrase 是响应短语，CRLF 是回车换行。

Header字段

格式:field-name: field-value

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Subject:            lunch
Subject      :      lunch
Subject            :lunch
Subject: lunch

以上都是正确的格式，但是Subject:lunch是最好的格式。

field-name相同的可以有多个，以下都是等价的

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Route: <sip:alice@atlanta.com>
Subject: Lunch
Route: <sip:bob@biloxi.com>
Route: <sip:carol@chicago.com>

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Route: <sip:alice@atlanta.com>, <sip:bob@biloxi.com>
Route: <sip:carol@chicago.com>
Subject: Lunch

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Subject: Lunch
Route: <sip:alice@atlanta.com>, <sip:bob@biloxi.com>,
       <sip:carol@chicago.com>

Route是有顺序的，以下两个是不等价的

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Route: <sip:alice@atlanta.com>
Route: <sip:bob@biloxi.com>
Route: <sip:carol@chicago.com>

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Route: <sip:bob@biloxi.com>
Route: <sip:alice@atlanta.com>
Route: <sip:carol@chicago.com>

field-name 是没有大小写区分的，但是field-value 是区分大小写的。
field-name 可以缩写，避免超过MTU.

Header缩写表

field-name	简写
Call-ID	i
Contact	m
Content-Encoding	e
Content-Length	l
Content-Type	c
From	f
Subject	s
Supported	k
To	t
Via	v

请求头必须有六要素:From, To, Call-ID, CSeq, Via, Max-Forwards

response头里的From,Call-ID,CSeq必须和request头里的相同。response的Via包含request的Via

如果request头里To没有tag,response的To里的URL必须和request的To的URL一样。

如何request头里To有tag,response的To必须和request的To一样。

无状态的UAS

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不会发送(1xx)response
不会重传response
忽略ACK request
忽略CANCEL request

CANCEL 最好只对INVITE 请求使用,不能包括RequireorProxy-Require头
REGISTER

response 带有Date字段，会通知client校准本地时间
response 不能带Record-Route字段,如果request带Record-Route字段, UAS要忽略掉。
expires的优先级高于Expires字段
200（OK）response必带Contact字段，以及expires参数

dialog

如果response没有收到route，UAC 必须把remote target uri 放到Request-URI里，然后请求不能加Route头
如果reponse收到route,并且route里的第一个uri包含lr字段， uac必须把remote target uri 放到Request-URI里，然后请求添加Route头，把respose的route放到Route头里。
如果response收到route,并且route里的第一个uri不包含lr字段， uac必须把route里的第一个uri去掉其他的参数放到Request-URI里，然后请求头添加Route,response的route放到Route头里。把remote target uri 放到``Route`最后。

例子：remote target is sip:user@remoteua and the route set contains: <sip:proxy1>,<sip:proxy2>,<sip:proxy3;lr>,<sip:proxy4>

那么请求为:

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METHOD sip:proxy1
Route: <sip:proxy2>,<sip:proxy3;lr>,<sip:proxy4>,<sip:user@remoteua>

如果uac收到2xx repsonse, 那么uac 必须使用response的Contact 作为remote target uri
如果uas收到request时，那么uas 必须把request的Contact作为 remote target uri来发送请求
uac 必须生成ACK request 为 2xx response, ACK的CSeq number和INVITE的CSeq number相同
uas 收到INVITE 没有SDP信息时，uas必须返回2xx response 带有SDP信息,这个就是（UPDATE）

Proxy流转

注意： mermaid不支持;目前使用|代替

基础流程

    sequenceDiagram
  actor U1 as U1<br/>u1.example.com
  participant P1 as P1<br/>example.com
  participant P2 as P2<br/>domain.com
  actor U2 as U2<br/>u2.domain.com
  U1->>P1: INVITE sip:callee@domain.com SIP/2.0<br/> Contact: sip:caller@u1.example.com
  P1->>P2: INVITE sip:callee@domain.com SIP/2.0 <br/> Contact: sip:caller@u1.example.com <br/> Record-Route: <sip:p1.example.com|lr>
  P2->>U2: INVITE sip:callee@u2.domain.com SIP/2.0 <br/> Contact: sip:caller@u1.example.com <br/> Record-Route: <sip:p2.example.com|lr> <br/> Record-Route:<sip:p1.example.com|lr>
  U2->>P2: SIP/2.0 200 OK <br/> Contact: sip:callee@u2.domain.com <br/> Record-Route: <sip:p2.domain.com|lr> <br/> Record-Route: <sip:p1.example.com|lr>
  P2->>P1: SIP/2.0 200 OK <br/> Contact: sip:callee@u2.domain.com <br/> Record-Route: <sip:p2.domain.com|lr> <br/> Record-Route: <sip:p1.example.com|lr>
  P1->>U1: SIP/2.0 200 OK <br/> Contact: sip:callee@u2.domain.com <br/> Record-Route: <sip:p2.domain.com|lr> <br/> Record-Route: <sip:p1.example.com|lr>
  U1->>P1: BYE sip:callee@u2.domain.com SIP/2.0 <br/> Route: <sip:p1.example.com|lr> <br/> Route:<sip:p2.domain.com|lr>
  P1->>P2: BYE sip:callee@u2.domain.com SIP/2.0 <br/> Route:<sip:p2.domain.com|lr>
  P2->>U2: BYE sip:callee@u2.domain.com SIP/2.0

严格路由流程

这是U1请求U2,但是经过中间P1,P2,P3,P4转发

    sequenceDiagram
  actor U1 as U1<br/>u1.example.com
  participant P1 as P1<br/>example.com
  participant P2 as P2<br/>example.com
  participant P3 as P3<br/>middle.com
  participant P4 as P4<br/>domain.com
  actor U2 as U2<br/>u2.domain.com
  U1->>P1: INVITE sip:callee@domain.com SIP/2.0<br/> Contact: sip:caller@u1.example.com
  P1->>P2: INVITE sip:callee@domain.com SIP/2.0 <br/> Contact: sip:caller@u1.example.com <br/> Record-Route: <sip:p1.example.com|lr>
  P2->>P3: INVITE sip:callee@domain.com SIP/2.0 <br/> Contact: sip:caller@u1.example.com <br/> Record-Route: <sip:p2.example.com|lr> <br/> Record-Route:<sip:p1.example.com|lr>
  P3->>P4: INVITE sip:callee@domain.com SIP/2.0 <br/> Contact: sip:caller@u1.example.com <br/> Record-Route: <sip:p3.middle.com> <br/> Record-Route:<sip:p2.example.com|lr> <br/> Record-Route:<sip:p1.example.com|lr>
  P4->>U2: INVITE sip:callee@u2.domain.com SIP/2.0 <br/> Contact: sip:caller@u1.example.com <br/> Record-Route: <sip:p4.domain.com|lr> <br/> Record-Route:<sip:p3.middle.com> <br/> Record-Route:<sip:p2.example.com|lr> <br/> Record-Route:<sip:p1.example.com|lr>
  U2->>P4: BYE sip:caller@u1.example.com SIP/2.0 <br/> Route: <sip:p4.domain.com|lr> <br/> Route:<sip:p3.middle.com> <br/> Route:<sip:p2.example.com|lr> <br/> Route:<sip:p1.example.com|lr>
  P4->>P3: BYE sip:p3.middle.com SIP/2.0 <br/> Route:<sip:p2.example.com|lr> <br/> Route:<sip:p1.example.com|lr> <br/> Route:<sip:caller@u1.example.com>
  P3->>P2: BYE sip:p2.example.com|lr SIP/2.0 <br/> Route:<sip:p1.example.com|lr> <br/> Route:<sip:caller@u1.example.com>
  P2->>P1: BYE sip:caller@u1.example.com SIP/2.0 <br/> Route:<sip:p1.example.com|lr>
  P1->>U1: BYE sip:caller@u1.example.com SIP/2.0

U1请求P1,P1转发U2

    sequenceDiagram
  actor U1 as U1<br/>u1.example.com
  participant P1 as P1<br/>p1.middle.com
  actor U2 as U2<br/>u2.domain.com
  U1->>P1: INVITE sip:callee@middle.com SIP/2.0<br/> Contact: <sip:caller@u1.example.com>
  P1->>U2: INVITE sip:callee@u2.domain.com SIP/2.0 <br/> Contact: <sip:caller@u1.example.com> <br/> Record-Route: <sip:p1.middle.com|lr>
  U2->>P1: SIP/2.0 200 OK <br/> Contact: <sip:callee@u2.domain.com> <br/> Record-Route: <sip:p1.middle.com|lr>
  P1->>U1: SIP/2.0 200 OK <br/> Contact: <sip:callee@u2.domain.com> <br/> Record-Route: <sip:p1.middle.com|lr>
  U1->>P1: BYE sip:callee@u2.domain.com SIP/2.0 <br/> Route: <sip:p1.middle.com|lr>
  P1->>U2: BYE sip:callee@u2.domain.com SIP/2.0