Re: [tsvwg] Last Call: <draft-ietf-tsvwg-rtcweb-qos-15.txt> (DSCP and other packet markings for WebRTC QoS) to Proposed Standard

Cullen Jennings <> Wed, 23 March 2016 22:45 UTC

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Subject: Re: [tsvwg] Last Call: <draft-ietf-tsvwg-rtcweb-qos-15.txt> (DSCP and other packet markings for WebRTC QoS) to Proposed Standard
From: Cullen Jennings <>
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Date: Wed, 23 Mar 2016 15:46:00 -0700
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To: Magnus Westerlund <>
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> On Mar 23, 2016, at 3:07 AM, Magnus Westerlund <> wrote:
> Hi,
> Below is the first round on a question, that looks like it needs to be addressed, thus I bring it into a public discussion.
> Den 2016-03-22 kl. 19:48, skrev Paul E. Jones:
> >> The other comment I have is the following:
> >>
>>> o Flow Type: The browser provides this input as it knows if the
>>>  flow is audio, interactive video with or without audio,
>>>  non-interactive video with or without audio, or data.
>>> Yes, a browser knows if a MediaStreamTrack's source is a live
>>> source, i.e. camera or microphone or a file. Which would indicate
>>> the difference between interactive or non. However, I don't
>>> understand what the Flow Type description for video contains "with
>>> or without audio" as the flow definitions in RTCWEB transport
>>> document all indicate flows as containing a single media type. Can
>>> you please clarify?
> >
>> This relates to the table that follows. The intent is that if a
>> WebRTC application is sending audio and video (e.g., a
>> videoconference call), then the same DSCP values might be used for
>> both the audio and video flows. On the other hand, if only a video
>> flow is sent alone (perhaps the audio source is an entirely different
>> device), then the browser can still use the same packet marking.
> So, I started commenting on this because, the "Flow Types" in the table are not really defined. And my interpretation was not that the audio could be given the same markings as the Video. I only interpreted it as being valid for the video flow. Thus, I think the actual "flow type" values in Table 1 needs to be better defined. To my knowledge these types are not defined in any other RTCWeb document.

Which codec it came from make is pretty clear if it is audio or video in the browser implementation. The word “flow”  has many meanings in all the different contexts but it seems like section 4 is pretty clear on breaking flow down into media and data types then breaking media down into the various types in the table and defining them. 

Are you getting at the issue of it a audio stream that is with a synchronized video stream can use the same markings as the video stream ? This tries to leave the options open and let people read things like  Section 4 of RFC 7657. 
> I think what is needed is a definition list for what is meant. I can see that pointers for example into RFC 4594 may help making these definitions more compact.
> One thing that might be a bit tricky is actually the difference between interactive and non-interactive (streaming) usages of WebRTC RTP streams. It becomes a question if the WebRTC endpoint actually accurately can classify these differences.

We decided at some point that if the browser is using SRTP, it is assumed to be interactive and the webrtc specs point at using this. If it is streamed over HTTP with something like DASH then it is non interactive and browsers could use the non interactive markings but I don’t think any of the streaming media docs have been updated yet to point that out. 

> Yes, a live media source, like an camera or microphone can on first order be used for classification as interactive, while a file source is non-interactive. But even the first, can in the application context be non-interactive. An example would be an lecturer application. Relaxing the delay from the lecturer to the audience is likely fine, especially if one have a "raise hand" mechanism and only explicitly invites participants to ask questions. To my knowledge there are no API surface to indicate these preferences on the MediaStream or MediaStreamTrack level.
> I think this document have a potential valuable difference for the interactive vs non-interactive, but the rest of the current solution has difficulties to utilize this difference. From my perspective I am fine with retaining the difference, but the definition must be clear so that implementers select the right one. And likely the non-interactive will not be much utilized until additional API knobs are created.

Agree but I think it is the WebRTC spec that needs to be clear on that, not this draft. 

> Cheers
> Magnus Westerlund
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