Re: [AVT] WGLC request for G.711.1 payload format

> 
> I had one question on this: what's the rationale for having 
> both fixed and dynamic modes? It would seem you could have 
> the same effect as the dynamic mode by signalling several RTP 
> payload types, and changing RTP payload type when you want to 
> change mode.
> 
> Colin
> 

Hi Colin,

I agree it seems equivalent and you can do everything with several fixed mode payload types. But in practice, it leads to some annoyances :
- it consumes a lot of payload types. If you want to declare the 4 current modes both in A-law and mu-law, it is 8 payload types. In the future we can expect more modes to be defined, like super-wideband quality, stereo... It will be 10, 12, ... payload types.
- it leads to a larger SDP, that could be a problem regarding the path MTU for SIP messages. Again, with more modes in the future, it will be worse.

G.711.1 is an embedded codec, all modes are supported by the standardized decoder, so there is no reason in my opinion to force separate payload type per mode. Dynamic mode currently is the default in the media type registration.
See RFC 4749 for G.729.1, it does not define a payload type per bit rate (12 would be needed). It is the same rationale.

In earlier (unpublished) version of the draft, I only defined the dynamic mode. Some reviewers have asked for a payload-header-free format, with fixed mode, so I added it. I think both have their use cases.

Do you think it is an issue to have the 2 options?

Regards,
Aurelien

> 
> 
> 
> On 9 Apr 2008, at 13:15, <aurelien.sollaud@orange-ftgroup.com> wrote:
> > Hi
> >
> > The ITU-T has approved G.711.1. Now a payload format RFC is needed.
> > I have updated the draft to update the reference and to fix some  
> > minor editorial things.
> >
> > I believe draft-ietf-avt-rtp-g711wb-01.txt is ready for WGLC.
> >
> > Thanks,
> > Aurelien
> >
> >
> >> -----Message d'origine-----
> >> De : avt-bounces@ietf.org [mailto:avt-bounces@ietf.org] De la
> >> part de Internet-Drafts@ietf.org
> >> Envoyé : mercredi 9 avril 2008 12:00
> >> À : i-d-announce@ietf.org
> >> Cc : avt@ietf.org
> >> Objet : [AVT] I-D Action:draft-ietf-avt-rtp-g711wb-01.txt
> >>
> >> A New Internet-Draft is available from the on-line
> >> Internet-Drafts directories.
> >> This draft is a work item of the Audio/Video Transport
> >> Working Group of the IETF.
> >>
> >>
> >> 	Title           : RTP Payload Format for ITU-T
> >> Recommendation G.711.1
> >> 	Author(s)       : A. Sollaud
> >> 	Filename        : draft-ietf-avt-rtp-g711wb-01.txt
> >> 	Pages           : 15
> >> 	Date            : 2008-04-09
> >>
> >> This document specifies a Real-time Transport Protocol (RTP)
> >> payload format to be used for the International
> >> Telecommunication Union
> >> (ITU-T) G.711.1 audio codec.  Two media type registrations
> >> are also included.
> >>
> >> A URL for this Internet-Draft is:
> >> 
> http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-g711wb-01.txt
> 
> 
> -- 
> Colin Perkins
> http://csperkins.org/
> 
> 
> 
_______________________________________________
Audio/Video Transport Working Group
avt@ietf.org
https://www.ietf.org/mailman/listinfo/avt