Subject: [MMUSIC] [draft-ietf-mmusic-sdp-media-capabilities] How to encode unknown format list?

From: "Belling, Thomas (NSN - DE/Munich)" <[email-masked]>
Date: Thu, 18 Aug 2011 19:48:04 +0200

Dear all

I would be grateful if you could help to clarify the following question,
which relates to ongoing discussions in 3GPP:

We need to express in a potential configuration  that we do not know the
used codecs.
(this can occur e.g.  in combination with draft-ietf-mmusic-sdp-cs)

draft-ietf-mmusic-sdp-media-capabilities-11 contains the following:

3.3.4.2.  The Payload Type Number Mapping Parameter (pt=)
...

   The "*" value for payload-type-number is used in cases such as BFCP
   [RFC4583] in which the fmt list in the m-line is ignored.

To be syntactically correct,  "pt=" requires a media-map-list, and thus
at least one numerical media-cap-num.

However, a couple of related questions pop up:
a.	Would a "m=" with the same media-cap-num also be required in the
potential configuration?
b.	Would a "a=mcap" attribute with the same media-cap-num also be
required in the SDP?
c.	Would it be also allowed to simply omit "pt=" in a potential
configuration?

In other words, which of the examples below are correct?

1.
a=mcap:1 -/-
a=tcap:1 PSTN
a=ccap:1 PSTN E164 +12125556666
a=pcfg:1 t=1 m=1 c=1

2.
a=mcap:1 -/-
a=tcap:1 PSTN
a=ccap:1 PSTN E164 +12125556666
a=pcfg:1 t=1 m=1 c=1 pt=1:*

3.
a=tcap:1 PSTN
a=ccap:1 PSTN E164 +12125556666
a=pcfg:1 t=1 m=1 c=1 pt=1:*

4.
a=tcap:1 PSTN
a=ccap:1 PSTN E164 +12125556666
a=pcfg:1 t=1 c=1 pt=1:*

Perhaps it might even be worth to add some clarifying words to the
quoted sentence above within the draft?

Many thanks in advance, Thomas

----------------------------------
Dr. Thomas Belling 
3GPP Standardisation 
Nokia Siemens Networks