[SIPForum-discussion] Offer_answer issue

[Tomasz Zieleniewski]

Hi,

Particular media and supported codecs are placed within media line
in SDP field within INVITE request. So if Your UA1 supports only one
codec it should placed it there.
The behavior of the UA2 depends on the type of the offered stream send by
the UA1.
If UA1 marked stream as receive only then m line in the response from UA2
must contain at least on media format from the offer but it can also
indicate
additional format it supports not listed in the offer from UA1.
If stream is send only then UA2 must specify at least one codec from those
received in the offer.
For send and receive streams m line in the answer from UA2 must contain
at least one codec from the offer and can contain additional codecs
for informational purpose. Codecs can't be used because they weren't
present in the offer. There is additional behavior sepcified for inactive
stream
but is very seldom case.

Kind regards,
- Tomasz Zieleniewski


2009/6/1 SINGH ANURAG <Anurag.Singh at alcatel-lucent.com>

>  Hi,
>
>
>
> Thanks for the input Tomasz.
>
> If I understood well than I hope you are saying that  the UA1 should send
> Offer with 8 in media line,
>
> now suppose 200OK still has multiple codec (like 18 8) in answer …
>
> So my question is that does it seem correct to send INVITE always.
>
> as it could be a unlimited exchange of messages
>
>
>
> Your opinion please
>
>
>
> Regards
>
> Anurag
>
>
>  ------------------------------
>
> *From:* Tomasz Zieleniewski [mailto:tzieleniewski at gmail.com]
> *Sent:* Monday, June 01, 2009 2:16 PM
> *To:* SINGH ANURAG
> *Cc:* discussion at sipforum.org
> *Subject:* Re: [SIPForum-discussion] Offer_answer issue
>
>
>
> Hi,
>
> In Your case UA1 should normally construct initial INVITE with SDP offer
> containing this particular codec specification. Despite any other non-media
>
> related reasons UA2 will reject INVITE with 488/606 (Not Acceptable Here)
> response
> in case the session description is not acceptable or will accept session
> offer by
> sending a final 2xx response with SDP answer containing the same codec
> specification.
> Provisional responses can also contain the same SDP contents as final 2xx
> one.
>
> Kind regards,
> Tomasz Zieleniewski
>
>  2009/5/29 SINGH ANURAG <Anurag.Singh at alcatel-lucent.com>
>
>
> Hello All,
>
> UA1 can open cahnnel only with one codec, so it need to negotiate with
> one codec
> I will take you to the example straight.
>
> UA1                                                     UA2
> -----INVITE(Offer m =0 8 18)----------->
> <-------200OK(Answer m=18 8)-----------
> --------INVITE(offer m=18)------------->
> <-------200OK(Answer m=8 18)------------
>
> what should be the behaviour?? is there any standred stating the
> behaviour
>
> Regards
> Anurag
>
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