Re: [AVT] CORRECTION W/ RFC EDITOR NOTE: Protocol Action: RTP PayloadFormat for SMPTE 292M Video to Proposed Standard

[Magnus Westerlund <magnus.westerlund@era.ericsson.se>]

Hi,

I reacted on the below in the RFC editors note that the IESG wrote.


The IESG wrote:

> **PLEASE NOTE RFC EDITOR NOTE.**
> RFC Editor: please make the following changes before publishing this ID
>
> Section 6, 1st paragraph
> OLD:
>
> RFC1889 recommends transmission of RTCP packets every 5 seconds or at a
> reduced minimum in seconds of 360 divided by the session bandwidth in
> kilobits/second. At 1.485 Gbps the reduced minimum interval computes to
> 0.2ms or 4028 packets per second.
>
> NEW:
>
> RTCP SHOULD be used as specified in RFC1889[3], which specifies two
> limits on the RTCP packet rate: RTCP bandwidth should be limited to 5%
> of the data rate, and the minimum for the average of the randomized
> intervals between RTCP packets should be 5 seconds. Considering the
> high data rate of this payload format, the minimum interval is the
> governing factor in this case.
>
> Section 13, 3rd and 4th paragraphs:
> OLD:
>
> [3] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, "RTP: A
>         Transport Protocol for Real-Time Applications", IETF, Work in
>         Progress (draft-ietf-avt-rtp-new-11.txt)
>         
> [4] H. Schulzrinee and S. Casner, "RTP Profile for Audio and Video
>         Conferences with Minimal Control", IETF, Work in progress,
>         (draft-ietf-avt-profile-new-12.txt).
>
> NEW:
>
> [3] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, "RTP: A
>         Transport Protocol for Real-Time Applications", IETF, January 1996,
>         RFC1889.
>
> [4] H. Schulzrinne and S. Casner, "RTP Profile for Audio and
>         Video Conferences with Minimal Control", IETF, January 1996,
>         RFC1890.
>  
I know that the referenced rule in the old text relies on one of the 
updates in the RTP spec about alternative minimal packet distances. So 
if it needs to be published now it can't have the old text. However I 
think that using the standard 5 seconds rule is rather useless from a 
RTCP usage point of view. In a payload format for sending 1.5 Gbit video 
data per second, a lot of packets will be sent during 5 seconds. So the 
intention of the SHOULD in the new text seems to me, to be not followed 
at all. In fact it seems that is should be actually be followed by 
recommendation to use a shorter minimal interval. But that interval 
shall not be shorter than what 360*1000/bitrate would give.

So I question if this really is a good edit. Would it not be better to 
clearly point out that another minimal interval than 5 seconds is 
recommended to be used. Either through a new text not relying on the 
updated RTP spec or actually refer to the new spec and let the 
publication hang until RTP as draft standard is published.

I guess that people actually going to use this format should give their 
opinion. From a RTP usage perspective I think this format is a case that 
really needs another minimal packet interval than 5 seconds and should 
not be published with the proposed new text.

Regards

Magnus Westerlund 
Multimedia Technologies, Ericsson Research ERA/TVA/A
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S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@era.ericsson.se



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