[MMUSIC] Feedback requested on requirements

[[e-mail] (Dale R. Worley)]

Here is the start of "compatibility" desiderata, that is, aspects of
the protocol needed to interwork well with the existing Internet.

   DES C1  In offer/answer usage, an endpoint using the bundle mechanism
      must interwork correctly with an endpoint that does not understand
      the bundle mechanism.

   DES C2  Interworking must continue when SDP endpoints are replaced
      with other endpoints during a sequence of offer/answer exchanges
      (such as happens in 3PCC or call transfers "behind an SBC"),
      including when a supporting endpoint is replaced by a non-
      supporting endpoint or vice-versa.

   SDP features (e.g., the codec set and ICE) are generally designed so
   that an offerer always offers every facility it is willing to support
   in the current situation, regardless of whether it was agreed to by
   the answerer in a preceding exchange.  Thus, if the current answerer
   is a different endpoint than the previous answerer, the new answerer
   will negotiate a compatible set of facilities without needing
   knowledge of its predecessor's SDP.  The offerer will smoothly
   transition to the new facilities.  This property is required to
   support 3PCC situations (e.g., [RFC3725] and
   [I-D.worley-service-example]).  This desideratum was suggested by
   Richard Ejzak.

Dale