[SR-Users] 488 Not Acceptable Here when remove codecs with rtcp-fb

[Juha Heinanen]

This 488 think reminds me that SIP over webrtc is broken.

Webrtc UAS (at least JsSIP) cannot issue 488 before the UAS has started
to ring.  It is very frustrating for the callee to get such a spam ring.

RFC3261 section "8.2 UAS Behavior" tells:

   Note that request processing is atomic.  If a request is accepted,
   all state changes associated with it MUST be performed.  If it is
   rejected, all state changes MUST NOT be performed.

So it is against the standard to issue 180 and after that reject the
request with 488.

-- Juha