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Re: PRACK: Does an early-session SDP offer fullfills the rule to insert SDP in first reliable response



 
Hi,

>>>You might consider the "early-session" mechanism specified by RFC
3959.
>>>But I have never heard of it being implemented, so it may not be 
>>>useful to you.
>> 
>>I have been assuming that we ARE talking about the 3959 mechanism, and

>>the question has been whether an "early-session" SDP offer fullfills 
>>the MUST rule to include SDP offer in the first reliable response.
>> 
>>IF we decide to relax the rule I guess it doesn't really matter, but 
>>if we maintain the rule I guess it is a valid question.
>
>Frankly I don't expect to see 3959 ever used. But if it is...

In IMS it is an alernative solution to providing some services. It is
optional to support, though.

>IMO the "early-session" and the "session" must each independently
comply with the o/a rules. So if you take any call flow 
>using early-session, and transform it in either of the following ways,
the transformed flow should still be valid 
>according to the normal rules for o/a using "session":
>
>1) remove all the body parts with content-disposition of
"early-session" 
>and content-type "application/sdp". Then if that results in
multipart/mixed body parts containing only an application/sdp 
>body part with c-d of session, remove the multipart, leaving just the
sdp in its place. Then remove any 
>Supported/Required references to early-session.
>
>2) remove all the body parts with content-disposition of "session" and
content-type "application/sdp". Then if that 
>results in multipart/mixed body parts containing only an
application/sdp body part with c-d of early-session, remove the 
>multipart, leaving just the sdp in its place. 
>Then replace occurrences of C-D:early-session with C-D:session. Then
remove any Supported/Required references to early-
>session.
>
>In theory, the above would allow the UAC to initiate both, but in
practice that would make no sense.
>
>If what I say is correct, then it relaxes no restrictions on anybody.

I am not sure I understand what you tried to explain :)

But, based on your arguments: according to the current rules, if the
first reliable SDP contains an early-session SDP offer, is it also
required to contain a session SDP offer? Or, I the early-session SDP
offer enough?

>I don't understand why anybody would bother with early-session. For the
cases where it might be useful I think the same 
>effect can be accomplished easier by simply establishing an early
dialog with one to-tag, and a different early/final 
>dialog with a different to-tag.

Why weren't you in 3GPP when I was arguing exactly the same thing... ;)

Regards,

Christer



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