[SIPForum-discussion] How to make Re-Invite without SDP

[M. Ranganathan]

On Sun, Jan 4, 2009 at 6:54 AM, Moshe Ostrovsky <mosheo at radvision.com> wrote:
> Hi,
>
>
>
> Re-Invite can be used for purpose of session-refresh (triggered by
> Session-timer mechanism) and in this situation no SDP is required.

 I assume that is one way of doing session timer, but re-INVITE
without SDP was not really intended for that.  Sending a re-INVITE
with the SAME sdp as the previous offer is a more elegant way of
implementing session timer and the way I have normally seen it done.


Here is a classic use of re-INVITE with no SDP. Consider the situation
when you need to do mid call media re-negotiation that needs to be
started by an intermediary ( for example an SBC ). In that case, the
SBC, acting as a B2BUA that stands in the middle of the signaling
between two dialogs that it is managing, solicits an offer from one of
the dialogs  ( lets call it side A) by sending it an INVITE without
SDP. Then plays the offer received in the OK from side A as a
re-INVITE to the other side ( lets call it side B) and plays the
answer back to the side A in an ACK with SDP when the answer is
received from  side B. This call flow is pretty useful when dealing
with call transfer through the SBC.

Regards,


Ranga

>
>
>
> Regards, Moshe.
>
>
>
> From: discussion-bounces at sipforum.org
> [mailto:discussion-bounces at sipforum.org] On Behalf Of Anthony Orlando
> Sent: Saturday, January 03, 2009 2:49 PM
> To: raghul82 at yahoo.co.uk; nitin kapoor
> Cc: discussion at sipforum.org
> Subject: Re: [SIPForum-discussion] How to make Re-Invite without SDP
>
>
>
> This issue has come up for me on a few occasions.  The purpose of the
> re-INVITE is to change the media characteristics.  If you send a re-INVITE
> without changing anything then it is breaking the spirit of the RFC,
> although I can't find anything that says it isn't allowed.
>
> --- On Fri, 1/2/09, nitin kapoor <nitinkapoorr at gmail.com> wrote:
>
> From: nitin kapoor <nitinkapoorr at gmail.com>
> Subject: Re: [SIPForum-discussion] How to make Re-Invite without SDP
> To: raghul82 at yahoo.co.uk
> Cc: discussion at sipforum.org
> Date: Friday, January 2, 2009, 8:19 PM
>
> Hello Raghul
>
> Can you please let us know where its shown that "we can send INivite without
> SDP" or if you have any docs for the same.
>
> Thanks
> Nitin Kapoor
>
> 2008/11/17 Raghul Prasanna <raghul82 at yahoo.co.uk>
>
> Hi Ranganathan,
>
>
>
>  I knew that in an initial call set up we can send INivite without SDP and
> in 200 OK we get SDP from the far end and we can ack with SDP...
>
>
>
>  I didnt know that we can have the same in reinvite..
>
>
>
> thanks for the info
>
>
>
> Raghul
>
> --- On Mon, 17/11/08, M. Ranganathan <mranga at gmail.com> wrote:
>
> From: M. Ranganathan <mranga at gmail.com>
> Subject: Re: [SIPForum-discussion] How to make Re-Invite without SDP
> To: raghul82 at yahoo.co.uk
> Cc: discussion at sipforum.org, "shiba shankar rout"
> <rout.shibashankar at gmail.com>
> Date: Monday, 17 November, 2008, 6:04 PM
>
>
>
> On Mon, Nov 17, 2008 at 10:33 AM, Raghul Prasanna <raghul82 at yahoo.co.uk>
>
> wrote:
>
>> HI Shiba,
>
>>
>
>>  I dont think we can reinvite without SDP, because the purpose of reinvite
>
>> is to change the media characteristics of a call after the call got
>
>> established..
>
>>
>
>>  Please can someone correct if I am wrong...
>
>
>
> You are corrected.
>
>
>
> You solicit an SDP offer using a Re-INVITE without SDP. The OK should
>
> have the SDP offer and you ACK with SDP to complete the 3-way
>
> handshake.
>
>
>
>>
>
>>   For generating PRACK, the invite shd have supported:100 rel parameter..
>
>>
>
>> Thanks,
>
>> Raghul
>
>> --- On Sun, 16/11/08, shiba shankar rout
>
> <rout.shibashankar at gmail.com>
>
>> wrote:
>
>>
>
>> From: shiba shankar rout <rout.shibashankar at gmail.com>
>
>> Subject: [SIPForum-discussion] How to make Re-Invite without SDP
>
>> To: discussion at sipforum.org
>
>> Date: Sunday, 16 November, 2008, 6:24 AM
>
>>
>
>> Hi everyone,
>
>>
>
>> I am not able to make re-invite without SDP. How to make re-invite without
>
>> SDP & with PRACK.
>
>> Is there any solution to this?
>
>>
>
>> Any hint would be welcome.
>
>>
>
>> Thanks
>
>> S S rout
>
>>
>
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>>
>
>
>
>
>
>
>
> --
>
> M. Ranganathan
>
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-- 
M. Ranganathan