FAQ: 200 OK without SDP when 100rel required

不少作 cisco voip gateway 维护的工程师认为对应 INVITE 的 200 OK 一定要有 SDP。碰巧 cisco 5400 某个版本的 IOS 在处理100rel 启用的呼叫时存在瑕疵，因此几次碰到拿这个问题说事，认为那些启用了 100rel 的呼叫在接通后断开是因为对应 INVITE的 200 OK 没有 SDP。

 

碰巧 Sip-implementors 邮件列表也有类似的答疑，

 

http://www.mail-archive.com/[email protected]/msg05936.html

 

> In RFC 3262, the behaviour allows for a reliable 18x response


> to carry the SDP answer.  So:


> 1. If SDP is in reliable 18x, the 200 OK does not need SDP. 


> 2. If SDP is in reliable 18x and SDP is in the 200 OK,


>     then the SDP of the 200 OK should be ignored.



http://www.ietf.org/internet-drafts/draft-ietf-sipping-sip-offeranswer-10.txt