[SIPForum-discussion] Re-Invite without SDP, No Audio Issue

[Dale R. Worley]

Harshal Patel <hpatel at aumtech.com> writes:
> [...] This Re-Invite does not have SDP.
>
>    1.
> *Should the SIP IVR put the audio on hold ? because no SDP is present. *
>    2. *Or Should the SIP IVR neglect the Re-INVITE and continue with the
>    call?*

The SIP IVR must (in its 200 response to the re-INVITE) send an SDP
offer.  This SDP must be a legitimate update of the SDP that it
previously sent within the dialog; in particular, media format numbers
that have been used previously must not be re-used for different codecs
than before.  It should also offer all codecs and media types that it is
willing to support (at this time), not just the ones that it is using in
the current media session.

The peer will send an ACK, which must contain an SDP answer to the SDP
offer that the SIP IVR sent in the 200.  At this point, the SIP IVR must
reconfigure its media processing to utilize the newly-negotiated media
session.

Dale