Re: [MMUSIC] I-D ACTION:draft-ietf-mmusic-sdp-media-capabilities-01.txt

["Robert R. Gilman" <[e-mail]>]

Ingemar-
Thanks for your comments.  Let me try to explain the approach we took.
Our intent was to associate each cfmt attribute with a codec in a cmed
attribute, in just the same way that the fmtp attribute is associated
with a codec (via payload type) in the media line.  We didn't consider
a mix-and-match at the codec level within the pcfg attribute.  I'll
most likely mess this up, but I believe the following is equivalent to
your SDP (you didn't seem to use the cmft:5 and cfmt:6 lines in your
description; doing so would cause the following example to perhaps be
even larger):

a=creq:1
a=cmed:1 AMR AMR AMR AMR AMR AMR
a=cmft:1 mode-change-capability=1; max-red-220; mode-set=0,2,4,7
a=cfmt:2 mode-change-capability=1; max-red=220; mode-set=0,3,5,6
a=cfmt:3 mode-change-capability=1; max-red-220; octet-align=1; mode-set=0,2,4,7
a=cfmt:4 mode-change-capability=1; max-red=220; octet-align=1; mode-set=0,3,5,6
a=cfmt:5 mode-change-capability=2; octet-align=1; mode-set=0,2,4,7
a=cfmt:6 mode-change-capability=2; octet-align=1; mode-set=0,3,5,6
a=cenc:1 16000/1
a=cenc:2 8000/1
a=cenc:3 16000/1
a=cenc:4 8000/1
a=cenc:5 16000/1
a=cenc:6 8000/1
m=audio 49152 RTP/AVP 97
a=rtpmap:97 AMR/16000/1
a=fmtp:97 mode-change-capability=2; max-red=220
pcfg:1 m=1|2 pt=1:98,2:99
pcfg:2 m=3|4 pt=3:98,4:99
pcfg:3 m=5|6 pt=5:98,5:99

My version takes about half again as many characters as yours.  There might
be a third way to do this as well - suppose the cfmt and cenc attributes
were applicable to multiple codecs, and multiple lines were applicable to
one codec (equivalent to your assumption).  Then we might say something like:

a=creq:1
a=cmed:1 AMR AMR AMR AMR AMR AMR
a=cenc:1,3,5 16000/1
a=cenc:2,4,6 8000/1
a=cfmt:1,2,3,4 mode-change-capability=1
a=cfmt:5,6 mode-change-capability=2
a=cfmt:1,2,3,5 max-red=220
a=cfmt:3,4,5,6 octet-align=1
a=cfmt:???? mode-change-neighbor=1
a=cfmt:???? mode-change-period=2
a=cfmt:1,3,5 mode-set=0,2,4,7
a=cfmt:2,4,6 mode-set=0,3,5,6
m=audio 49152 RTP/AVP 97
a=rtpmap:97 AMR/16000/1
a=fmtp:97 mode-change-capability=2; max-red=220
pcfg:1 m=1|2 pt=1:98,2:99
pcfg:2 m=3|4 pt=3:98,4:99
pcfg:3 m=5|6 pt=5:98,5:99

This form takes slightly fewer characters than yours (I left in the
two format parameters you didn't seem to use), but I'm not sure which
one is more useful or readable.  Both permit the SDP generator to code
format parameters on multiple lines, rather than force one long line,
but still permit it if desired.  Codecs with lots of formatting parameters
and options are always problematic in capability announcements - unless
you can declare lot of "don't-care" values or use popular defaults.
It seems almost any method will do if there is little reuse of parameters.
What do you think?
-Bob
----------------------------------------------------
Bob Gilman       [e-mail]      [phone]

Ingemar Johansson S (LU/EAB) wrote:
> Hi
> 
> Reading the draft I have the following simple question 
> Would it be possible, based on all the possible attributes given in 
> http://tools.ietf.org/id/draft-ietf-avt-rtp-amr-bis-06.txt
> to formulate an SDP offer like the one below. 
> I am not sure that it is possible to combine several cmft's in the pcfg
> in the f=x,y,z.. way that I written below, it is possible that it is
> sematically incorrect, anyway comments welcome.
> Regards
> Ingemar
> ======================== 
> a=creq:v1
> a=cmed:1 AMR
> a=cfmt:1 mode-change-capability=1;
> a=cfmt:2 mode-change-capability=2;
> a=cfmt:3 max-red=220;
> a=cfmt:4 octet-align=1;
> a=cfmt:5 mode-change-neighbor=1; 
> a=cfmt:6 mode-change-period=2;
> a=cfmt:7 mode-set=0,2,4,7;
> a=cfmt:8 mode-set=0,3,5,6;
> a=cenc:1 16000/1
> a=cenc:2 8000/1
> m=audio 49152 RTP/AVP 97
> a=rtpmap:97 AMR/16000/1
> a=fmtp:97 mode-change-capability=2; max-red=220
> pcfg:1 m=(1 f=1,3,7 e=1 pt=98)|(1 f=1,3,8 e=2 pt=99)
> pcfg:2 m=(1 f=1,3,4,7 e=1 pt=98)|(1 f=1,3,4,8 e=2 pt=99)
> pcfg:3 m=(1 f=2,4,7 e=1 pt=98)|(1 f=2,4,8 e=2 pt=99)
> ======================== 
> 
> 
>>-----Original Message-----
>>From: [e-mail] [mailto:[e-mail]] 
>>Sent: den 21 februari 2007 16:50
>>To: [e-mail]
>>Cc: [e-mail]
>>Subject: [MMUSIC] I-D 
>>ACTION:draft-ietf-mmusic-sdp-media-capabilities-01.txt
>>
>>A New Internet-Draft is available from the on-line 
>>Internet-Drafts directories.
>>This draft is a work item of the Multiparty Multimedia 
>>Session Control Working Group of the IETF.
>>
>>	Title		: SDP media capabilities Negotiation
>>	Author(s)	: F. Andreasen, et al.
>>	Filename	: 
>>draft-ietf-mmusic-sdp-media-capabilities-01.txt
>>	Pages		: 22
>>	Date		: 2007-2-21
>>	
>>Session Description Protocol (SDP) capability negotiation provides a
>>   general framework for negotiating capabilities in SDP.  The base
>>   framework defines only capabilities for negotiating transport
>>   protocols and attributes.  In this document, we extend the 
>>framework
>>   by defining media capabilities that can be used to negotiate media
>>   types and their associated parameters.
>>
>>A URL for this Internet-Draft is:
>>http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdp-medi
>>a-capabilities-01.txt
>>
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