Subject: RE: [Sip] Reinvite query

From: "Christian Jansson" <[email-masked]>
Date: Wed, 24 Aug 2005 10:46:53 +0200

>Hi,
>    Considering B may want to connect A to some other resources in this
way
>(like 3PCC),  and the new media connection may be bi-directional or
>uni-directional.
>
>It better for A to provide the full capability  in 200 OK SDP(ie,
>a=sendrecv), and leave the flexibility of making final decision to B or
>some other service logic behind him.

With "full capability" I suppose you mean that the SDP should contain
all supported media types like audio, video, text, message, and
application. All media types should be in sendrecv mode which would mean
that a lot of listening resources had to be started. 

Is this the correct interpretation of your statement?

/ Christian Jansson

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---

From: Troy Cauble <[email-masked]>
Date: Wed, 24 Aug 2005 13:33:15 -0400

> From:
> "Christian Jansson" <[email-masked]>

> Is this the correct interpretation of your statement?

 From RFC 3261, section 14:

    A UAS providing an offer in a 2xx (because the INVITE did
    not contain an offer) SHOULD construct the offer as if the
    UAS were making a brand new call, subject to the constraints
    of sending an offer that updates an existing session, as
    described in [13] in the case of SDP.

But RFC 3264 puts some restrictions on how the the SDP can differ
from the previous SDP provided, including:

    If an SDP is offered, which is different from the previous SDP, the
    new SDP MUST have a matching media stream for each media stream in
    the previous SDP.  In other words, if the previous SDP had N "m="
    lines, the new SDP MUST have at least N "m=" lines.

-troy