FAQ: 200 OK without SDP when 100rel required

不少作 cisco voip gateway 維護的工程師認爲對應 INVITE 的 200 OK 一定要有 SDP。碰巧 cisco 5400 某個版本的 IOS 在處理100rel 啓用的呼叫時存在瑕疵，因此幾次碰到拿這個問題說事，認爲那些啓用了 100rel 的呼叫在接通後斷開是因爲對應 INVITE的 200 OK 沒有 SDP。

 

碰巧 Sip-implementors 郵件列表也有類似的答疑，

 

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