Subject: [MMUSIC] [mmusic-t140-usage-data-channel]: "a=dcsa" for T.140 cps parameter

From: "Schwarz, Albrecht (Albrecht)" <[email-masked]>
Date: Tue, 6 Oct 2015 08:15:13 +0000

Dear All,

the discussion about "SDP limitations" at SLIM (see
https://mailarchive.ietf.org/arch/msg/slim/C-82-NRgfR50mVTkM_wklrKw0SY )
spotted an issue in draft-schwarz-mmusic-t140-usage-data-channel-02.txt
related dcsa usage:

We've used (in clause 5.1.1.3. Example SDP Negotiation)
	a=dcsa:1 cps=30
which misses the fmtp parameter (see RFC 4103).

It was proposed to use instead e.g.
	a=dcsa:1 fmtp:- cps=30

The reason why we omitted the fmtp parameter is the fact that the binding is already provided by the dcsa stream-id value, hence fmtp is not required, just introduces redundancy.

However, we will update the example as suggested by Christian due to consistency reasons with draft-ietf-mmusic-data-channel-sdpneg:
   Syntax:
   dcsa-value      = stream-id SP attribute
   attribute       = <from-RFC4566>

Any further comments?
Albrecht

---

From: Gunnar Hellström <[email-masked]>
Date: Tue, 6 Oct 2015 18:59:49 +0200

>     attribute       = <from-RFC4566>
Is this really a sufficient way to describe the attribute?
When used directly in sdp, fmtp: is supposed to have a format number as 
parameter, then followed by format specific parameters specified in RFC 
4102 and RFC 4103.
The format specific parameters can be the redundancy format list and the 
cps= parameter.

Questions:
1. Is it specified somewhere that the dash - can be used to represent 
one or more parameter(s) that can be ignored?
2. Is it sufficient to describe as above that the attribute has its 
syntax from RFC 4566? Or would RFC 4102 and RFC 4103 also need to be 
mentioned to explain the structure of the fmtp: parameters for this codec?
3. If it is problems to specify a direct mapping of this fmtp 
attribute,  can instead an attribute native to the subprotocol be 
specified and its mapping to the fmtp parameter be specified in the 
gatewaying specification?

/Gunnar

>
> Any further comments?
> Albrecht
>
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