Subject: RE: RE : [AVT] [Fwd: I-DACTION:draft-sollaud-avt-rtp-g729-scal-wb-ext-00.txt]

From: "SOLLAUD Aurelien RD-TECH-LAN" <[email-masked]>
Date: Mon, 18 Apr 2005 18:04:21 +0200

> 
> I have a comment regarding the MBS signalling, since it's not 
> clear if this MBS signals the maximum bit rate of the 
> decoder, or of the network path. If the latter, I think the 
> draft will need to discuss more about how the MBS relates to 
> congestion control via, for example, TFRC, and how the bit 
> rate can be estimated in IP networks.

The MBS is the maximum bit rate of the decoder. Between 8 and 32 kbps.
The related network bit rate will of course be (much) higher due to the
Access/IP/UDP/RTP/PayloadHeader overhead and thus depends on the number
of frames par packet, the physical layer (Eth, ATM, PPPoE ...).

The use of the MBS is optional and is application-driven.
If you have a PC VoIP software on a LAN, you will not modify MBS and the
maximum rate of 32 kbps will be used.
If you have a 56k dial-up connection you may like to have an option to
decrease the MBS if you want to download a file faster while talking
and, after, increase back the MBS = the quality.
If the software is embedded in a residential gateway with analog phones
plugged in, with a limited network channel reserved for the VoIP
telephony, the rate must be dynamically adapted to the number of
simultaneous calls with the outside. In this example the MBS will be
modified on a call event occurrence, like, a second call is taking
place, the first one hangs up etc... The actual values of MBS and
thresholds in terms on number of calls will be written in the
residential gateway by the manufacturer, depending on the total
bandwidth reserved to telephony.
Note that you can also use the MBS reduction to indirectly decrease the
CPU cost of the decoding process, which may be useful on low-cost
hardwares to perform other long operations. 

I agree This MBS section of the draft should be reworked to add more
text and not just an example.

> 
> Otherwise, this looks to be a straight forward payload format 
> design, with no major complications.

Great.

> Colin

Thanks for your review
Aurelien 

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt