[SIPForum-discussion] P-Early-Media and Offer-Answer Relation

[Stephen James]

Read - http://tools.ietf.org/html/rfc6337
This indicates that if the 183 is not reliable, then the offer/answer is not complete until the reliable (200 OK, or 18x w/ 100rel) is received.
There is some confusion in that the spec says that the UAC should treat the 183 SDP as a preview of the final answer and that it should not change in the 200 OK.
RFC 3261 says:


If the initial offer is in an INVITE, the answer MUST be in a reliable non-failure message from UAS back to UAC which is correlated to that INVITE.  For this specification, that is only the final 2xx response to that INVITE.  That same exact answer MAY also be placed in any provisional responses sent prior to the answer.  The UAC MUST treat the first session description it receives as the answer, and MUST ignore any session descriptions in subsequent responses to the initial INVITE.

But I am not sure what happens if the 2xx is not the same as the 183 in your case. We have interworked with an Ericsson
switch which will fail the call if an unexpected SDP or SDP version change is received.



 
Stephen James 
sjames_1958 at yahoo.com
 
We are not princes of the earth, we are the descendants of worms, and any nobility must be earned.



________________________________
 From: Pranav Damele <pranavdamele at gmail.com>
To: ankur bansal <abh.ankur at gmail.com> 
Cc: "discussion at sipforum.org" <discussion at sipforum.org> 
Sent: Saturday, June 15, 2013 8:26 AM
Subject: Re: [SIPForum-discussion] P-Early-Media and Offer-Answer Relation
 


Hello Ankur,

I believe you should use UPDATE method when an early-media has been established and you need to modify the characteristics of that session rather than 200 OK.


Regards,

Pranav Damele
ARICENT
Senior Engineer - Testing

Mobile: +91-9818-92-4466
Email: pranavdamele at gmail.com
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On 14 June 2013 16:04, ankur bansal <abh.ankur at gmail.com> wrote:

Hi All ,
>
>
>I have come across one sceanrio :
> 
>Invite sdp(O1)---------------------->
>183 sdp V1(A1) <----------------------
>200 sdp V2 <-----------------------------
>ACK ------------------------------------->
>
>
>Here Sdp coming in 183 and 200 is same but server sending diff versions for both.
>As offer answer is complete after 183 sdp ,how should we handle  200 sdp ?
>  1. Assuming 200 sdp as new offer and send answer in ACK ?
>  2. Ignore 200 sdp as offer answer already completed ?
>
>
>Also note 183 is coming with P-Early-Media header .
>Does P-Early-Media in 183 response gives us any flexibility regarding Offer answer model or not ?
> 
>
>
>
>Thanks & regardsAnkur Bansal
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