[Sip] Re: [Sip-implementors] Early media query

["Retesh Chadha" <retesh.chadha at gmail.com>]

Hi Udit
Of all the methods you have specified, Method 1 and 2 are wrong as per
the RFC which states that the sdp of all the provisional and 2xx
response of INVITE should be same if they are present.

Both Method 3 and 4 look fine, with method 4 being better because in
that case 200 ok for INVITE is only sent when the final negotiation
(call media) is done.

Hope this helps.
--
With Regards
Retesh Chadha


On 10/2/06, Udit_Goyal at 3com.com <Udit_Goyal at 3com.com> wrote:
> Hi,
>
> I want to made an application where we can use early media for playing
> initial in-band announcements, and then finally connecting the caller to
> actual callee (eg prepaid card application).
>
> I want to know which is the correct way to support this as per SIP RFC.
>
> Method 1:
>
>
>                 Caller                        Callee
>                   |                             |
>                   |                             |
>                   |(1) INVITE with offer        |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(2) 183 with answer 1        |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(3) 200 OK with SDP          |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(4) ACK                      |
>                   |---------------------------->|
>                   |                             |
>
>
> (2) contains SDP of announcement server
> (3) contains SDP of callee
>
>
> Method 2:
>
>                                        Caller Callee
>                   |                             |
>                   |                             |
>                   |(1) INVITE with offer        |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(2) 183 with answer 1        |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(3) PRACK                    |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(4) 200 PRACK                |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(5) 200 INVITE with sdp      |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(6) ACK                      |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |                             |
>                   |                             |
>
> (2) contains SDP of announcement server
> (5) contains SDP of callee
>
>
> Method 3:
>
>        Caller                        Callee
>                   |                             |
>                   |                             |
>                   |(1) INVITE with offer        |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(2) 183 with answer 1        |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(3) PRACK                    |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(4) 200 PRACK                |
>                   |<----------------------------|
>                   |(5) 200 OK                   |
>                   |<----------------------------|
>                   |                             |
>                   |(6) ACK                      |
>                   |---------------------------->|
>                   |                             |
>                   |(7)Re-INVITE with SDP        |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(8) 200 OK with SDP          |
>                   |---------------------------->|
>                   |                             |
>                   |(9) ACK                      |
>                   |---------------------------->|
>
> (2) contains SDP of announcement server
> (5) contains no SDP
> (7) contains SDP of callee
> (8) contains answer of caller for callee offer
>
> Her, UDATE can also be used instead of Re-invites.
>
> Method 4:
>
>                                            Caller Callee
>                   |                             |
>                   |                             |
>                   |(1) INVITE with offer        |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(2) 183 with answer 1        |
>                   |<----------------------------|
>                   |                             |
>                   |                             |
>                   |(3) PRACK                    |
>                   |---------------------------->|
>                   |                             |
>                   |                             |
>                   |(4) 200 PRACK                |
>                   |<----------------------------|
>                   |(5) UPDATE (callee offer)    |
>                   |<----------------------------|
>                   |                             |
>                   |(6) 200 UPDATE (answer)      |
>                   |---------------------------->|
>                   |                             |
>                   |(7) 200 INVITE                   |
>                   |---------------------------->|
>                   |                             |
>                   |(8) ACK                      |
>                   |---------------------------->|
>
>
> In this case, when callee answers, UPDATE is sent to caller to negoitate
> audio with caller, and then 200 OK is sent for the initial INVITE.
>
> Regards,
> Udit
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