[SIPForum-discussion] Offer/Answer Model

[Vivek Batra]

As per RFC 3261, SDP can be negotiated in INVITE and 200OK or 200 OK and
ACK.
At the same time, unreliable response viz 183 Session Progress can also have
SDP answer for early media. However, unreliable response can not have SDP if
first INVITE hadn't SDP offer.

RFC3262 defines the SDP negotiation in reliable provisional responses where
SDP can be negotiated between:
INVITE and reliable response (180 Ringing)
180 Ringing and PRACK
PRACK and 200 OK (of PRACK)

At any time during early dialog once the SDP has been negotiated, caller or
callee can again send the offer in UPDATE.

Now as per your question regarding how to identify the SDP is Offfer or
Answer, the first SIP message which includes SDP is alwyas Offer and
subsequent SIP message which includes SDP would be SDP Answer!!

--Vivek

On Wed, Aug 20, 2008 at 3:24 AM, zabi <mohamed.zabiulla at gmail.com> wrote:

>   Dear All,
>
>     As per my knoweldge, Offer/Answer can occur in INVITE/2XX/ACK.
>
> Given a Sip message containing SDP how do we differentiate whether it is an
> OFFER/ANSWER??
>
>
> Regards,
> Zabi
>
>
>
>
>
>
> --
> why run? you'll only die tired!!
> Zabi.
>
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