Re: [dispatch] Draft on Discarding Priority of RTP Video Packets

[Magnus Westerlund <[e-mail]>]

Hi Lijun,

I am trying to understand what is the actual problem you are trying to solve here?

I would like to point out that you haven’t take to hard the recommendations in the DART RFC: https://datatracker.ietf.org/doc/rfc7657/ into account as you are mixing AF traffic classes for a stream. That can result in reordering, if that is to large to make the RTP receiver buffer unhappy is hard to be certain of, but likely a particular RTP stream should stay within one AF class and only modulate drop precedences.

Neither does it look like you have looked at the specification that do exist in this space, namely the one on QoS for WebRTC where https://datatracker.ietf.org/doc/rfc8837/ is most relevant but you likely should look at https://datatracker.ietf.org/doc/rfc8835/ also. This do create priority based usage of DSCP based on the common classes.

I think the real problems in this space are primarily. First knowing which DSCP you can actually use, i.e. are you knowing and allowed to use the DSCP values you want to use in this local domain and will they survive and be meaningful into the relevant domains?

The other issue that Roni Even’s draft goes more into is how to you figure out what you can actually drop in a reasonable way to have minimal long term effects. Trying to do this efficiently without maintaining state like a MANE can do, is actually hard. And in most cases when one packet have been dropped as part of a structure, it would be best to drop all. But that can’t really be communicated in DSCP.

Also, you appear to not have made AVTCORE WG aware of this work. I would think that this is would be highly relevant to that WG.

Cheers

Magnus

From: dispatch <[e-mail]> on behalf of Lijun Dong <[e-mail]>
Date: Wednesday, 13 July 2022 at 02:00
To: [e-mail] <[e-mail]>
Cc: Stuart Clayman <[e-mail]>, Muge Sayit <[e-mail]>
Subject: [dispatch] Draft on Discarding Priority of RTP Video Packets
Hi dispatch:

I want to share my recently submitted draft on “Discarding Priority of RTP Video Packets”.

https://datatracker.ietf.org/doc/draft-dong-priority-rtp-packet/<https://protect2.fireeye.com/v1/url?k=31323334-501d5122-313273af-454445555731-a41c44a64e6e38d4&q=1&e=c47fec5d-9c95-49a5-b2d2-0151f0c0a813&u=https%3A%2F%2Fnam11.safelinks.protection.outlook.com%2F%3Furl%3Dhttps%253A%252F%252Fdatatracker.ietf.org%252Fdoc%252Fdraft-dong-priority-rtp-packet%252F%26data%3D05%257C01%257Clijun.dong%2540futurewei.com%257Cf4f099e6e73948d8ec8b08da645f3cd2%257C0fee8ff2a3b240189c753a1d5591fedc%257C1%257C0%257C637932657449689304%257CUnknown%257CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%253D%257C3000%257C%257C%257C%26sdata%3DZ1%252BLmuaJWeZHd6TIDI%252F0o3ukSdRXRNi8oZb1hKaxYro%253D%26reserved%3D0>

It is observed that significance difference or discarding priority might exist among RTP packets which encapsulate video streaming data with the existing modern video codecs. So selectively dropping RTP packets according to their significances could be a complementary mechanism when dealing with network congestion and improve end user’s QoE. The draft proposes that the video source or edge node with media-awareness could perform mapping of RTP packet discarding priority carried in RTP NALU header to a DSCP value, such that the priority-based dropping could happen at the packet level when network congestion happens.

I look forward to your generous comments and suggestions.

Lijun