sip 协议 --PRACK
1. 概念 ： sip 协议中的PRACK 英文全称：Provisional Response ACKnowledgement 。临时恢复确认。
详细描述在：RFC3262中 http://www.ietf.org/rfc/rfc3262.txt
2. 目的：确保sip中 1xx 响应的可靠传输。 PRACK一般是对收到183 call in progress/180 ringing的确认，
3.实例1 ：sip:[email protected] 发送INVITE请求到sip:[email protected]
Supported 头域中：带有100rel。 但是sip:[email protected] 不支持100rel 扩展。就回复 420 Bad extension (unsupported)
消息流：
INVITE sip:[email protected]:5060 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.112:5060;rport;branch=z9hG4bKPj0693c29ace0342c4a795524325069634
Max-Forwards: 70
From: "6034"
To:
Contact:
Call-ID: 3c746f1e06db45c0a87d2c93f21d76da
CSeq: 19095 INVITE
Allow: INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, SUBSCRIBE, NOTIFY, REFER, OPTIONS, MESSAGE
Supported: replaces, 100rel, timer
Require: 100rel
User-Agent: AT940 V1.0.0
Content-Type: application/sdp
Content-Length: 430
v=0
o=ATCOM 3587281334 3587281334 IN IP4 192.168.1.112
s=ATCOM Audio Call
c=IN IP4 192.168.1.112
t=0 0
m=audio 16384 RTP/AVP 0 4 8 9 98 18 108 101
c=IN IP4 192.168.1.112
a=sendrecv
a=rtpmap:0 PCMU/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:9 G722/8000
a=rtpmap:98 iLBC/8000
a=fmtp:98 mode=30
a=rtpmap:18 G729/8000
a=rtpmap:108 G726/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:10
SIP/2.0 420 Bad extension (unsupported)
Via: SIP/2.0/UDP 192.168.1.112:5060;branch=z9hG4bKPj0693c29ace0342c4a795524325069634;received=192.168.1.112;rport=5060
From: "6034"
To:
Call-ID: 3c746f1e06db45c0a87d2c93f21d76da
CSeq: 19095 INVITE
Server: Asterisk PBX SVN--r2564M
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, PUBLISH
Supported: replaces, timer
Date: Wed, 04 Sep 2013 11:02:03 GMT
Unsupported: 100rel
Content-Length: 0
ACK sip:[email protected]:5060 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.112:5060;rport;branch=z9hG4bKPj0693c29ace0342c4a795524325069634
Max-Forwards: 70
From: "6034"
To:
Call-ID: 3c746f1e06db45c0a87d2c93f21d76da
CSeq: 19095 ACK
Content-Length: 0
4.实例2：sip:[email protected] 发送INVITE请求到sip:[email protected]
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP 192.168.1.120:5060;received=192.168.1.120;branch=z9hG4bK144c5a17
Call-ID: [email protected]:5060
From: "6089"
To:
CSeq: 102 INVITE
Contact:
Allow: INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, SUBSCRIBE, NOTIFY, REFER, OPTIONS, MESSAGE
Require: 100rel
RSeq: 1225
Content-Length: 0