[SIPForum-discussion] Offer/Answer Model

[Yajuvendra Singh]

Hi,

As far as my knowledge, just by looking at a sip message you can not guess
whether it is a offer or and answer, but i think in QOS related flows you
can make out whether it is a offer or a answer, because there are some "a"
lines in which the client need to tell the qos allocation status so i guess
u can make it out from qos related flows.

infact you can have a offer in 200 ok of invite and the call initiator can
send the answer in ACK as far a rfc3261 goes.

you can refer to rfc 4317 "http://tools.ietf.org/html/rfc4317" this states
the offer answer examples.

Regards
Yajuvendra


On Thu, Aug 21, 2008 at 12:00 AM, Vivek Batra <vivek7683 at gmail.com> wrote:

> 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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>
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-- 
Yajuvendra

"Dream as if you'll live forever; Live as if you'll die
today"
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