[SIPForum-discussion] Regarding Offer/Answer Model

[saraswati sp]

Thanks a lot.

Currently exploring on Offer/Answer. So need to make sure whether am moving
in right direction. So plz guide me.

So now the first SIP message that includes SDP is offer and the latter sip
message containing SDP will be Answer.

In order to know whether SDP is present or not, we need to check
the presence of header field "Content-type". which is mandatory header
field.

According to RFC 3261 "The Content-Type header field MUST be present if the
body is not empty. If the body is empty, and a Content-Type header field is
present, it indicates that the body of the specific type has zero length".

So is the presence of SDP known only by this header field or any other??

Thanks in advance.


On Wed, Aug 20, 2008 at 10:46 PM, Vivek Batra <vivek7683 at gmail.com> wrote:

> Hi,
> 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!!
>
> I hope, you would get brief overview.
>
> --Vivek
>
>
>
> On Wed, Aug 20, 2008 at 3:51 AM, saraswati sp <saraswatisp 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,
>> Saraswati.
>>
>>
>>
>>
>>
>
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