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When testing SIP calls on the SIP server that we are developing i came across a case where the 200Ok response for UPDATE message arrives after 180 ringing is received on the SIP server. In other words the device at B sends 180 Ringing to the server before sending the 200OK response for UPDATE. The call flow is per the attached image - Late 200OK response image. The question is- Is this correct with respect to call flow. Does the standard allow this. Is the device B at fault?

I tried to get answer from web and RFCs but unable to get correct information. Can someone point me in the right direction on how to handle this situation?

Balaji Bakthavachalam
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  • This is off topic here, as it's not a programming question. – nos Dec 18 '15 at 18:34
  • Not a programming question. I recommend you to add more details for the SIP stack you are using or contacting the correct email alias. (Asterisk Freeswitch, Kamailio, etc..) – gogasca Dec 21 '15 at 18:43

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It's valid from the standard. And there is no reason it should break anything in your app. 200 Ok for UPDATE has one meaning: the UPDATE was correctly received/handled on remote side. No matter when you receive it!

As a sidenote, User B should not send 183 and later a 180: provisionnal response status code sent by one same User-Agent should always increase. That doesn't look to be your question, but worth to be pointed out!

AymericM
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