Subject: Re: [AVT] WGLC on draft-ietf-avt-rtp-ipmr-04

From: Colin Perkins <[email-masked]>
Date: Mon, 8 Jun 2009 16:53:21 +0100

On 26 May 2009, at 08:35, Roni Even wrote:
> I would like to start a WGLC on http://tools.ietf.org/html/draft-ietf-avt-rtp-ipmr-04 
>  .
>
> This is the RTP Payload Format for IP-MR Speech Codec.
>
> There was some comments on the mailing list about this work and they  
> were addressed in the 04 draft.
>
> We will start a 3 weeks working group last call.
> Please review the draft and send comments till June 16th

I have several comments on this draft:

The payload header includes flags (the "D" and "A" bits) to signal if  
DTX is allowed, and if the payload format is byte aligned. This is  
unusual. Previous payload formats generally signal such parameters out- 
of-band, for example using an SDP offer/answer exchange. What's the  
rationale for this design, and is there a reason why out-of-band  
parameters cannot be used?

The A bit in the payload header signals whether a byte-aligned mode is  
to be used. There doesn't seem to be any specification of how this  
differs from the non-byte-aligned mode.

Section 3.5 indicates that the decoder "can calculate the frame size  
by its content" and notes that "there is a special service function  
that returns frame size without total decoding which may be used for  
this purpose". A function tied to a particular codec implementation is  
appropriate for a vendor codec, but not for a payload format that is  
to be registered in the standards tree. The draft needs to document  
how to determine the payload length. (this information might be added  
to the table on page 6).

Page 8 includes a table listing the amount of redundancy that might be  
added. This is listed as being class A, B, C, D, E, or F, but no  
details are provided on what each means. If this is to be a standard  
media type, more details must be provided, to allow independent  
implementation of the payload format.

-- 
Colin Perkins
http://csperkins.org/

---

From: "Elena Berlizova" <[email-masked]>
Date: Tue, 16 Jun 2009 18:27:34 +0400

-----Original Message-----
From: Elena Berlizova 
Sent: Monday, June 15, 2009 3:33 PM
To: [email-masked]'
Cc: 'Tom Taylor'; 'Roni Even'; Sergey Ikonin
Subject: RE: [AVT] WGLC on draft-ietf-avt-rtp-ipmr-04

Hi all,

Addressing Colin's comments: 

	[SI]-> When we developed payload format we tend to maximize
flexibility of codec usage in real-time to allow rapid channel
adaptation. Because of that we put all codec setting in-band to allow
quick changing of it without re-negotiation. Now we think these two
can be placed out-of-band. But some our customers already deployed
this format and we need to keep interoperability with them.

	[SI]-> In sec 4.2 we have example of payload format in which the
A=1. 	In this example all speech frames are padded with zero bits for
byte 	alignment. This is the difference from non-byte-aligned mode.

how to determine the payload length. (This information might be added  
to the table on page 6).

	[SI]-> We can add some table to indicate frame size depending of
first 	bits and codec settings. But we afraid that table will be big
enough 	and not clear for usage. Another option which we can do - to add
some 	function in c-code or pseudo-code that return frame size
depending of 	frame content and codec settings.

Yours sincerely
Elena Berlizova

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Colin Perkins
Sent: Monday, June 08, 2009 7:53 PM
To: Roni Even
Cc: [email-masked]; 'Tom Taylor'
Subject: Re: [AVT] WGLC on draft-ietf-avt-rtp-ipmr-04

On 26 May 2009, at 08:35, Roni Even wrote:
> I would like to start a WGLC on
http://tools.ietf.org/html/draft-ietf-avt-rtp-ipmr-04 

-- 
Colin Perkins
http://csperkins.org/

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Audio/Video Transport Working Group
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