[Wish] Re: Zaheduzzaman Sarker's Discuss on draft-ietf-wish-whip-14: (with DISCUSS and COMMENT)

Zaheduzzaman Sarker <zahed.sarker.ietf@gmail.com> Thu, 23 May 2024 14:36 UTC

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From: Zaheduzzaman Sarker <zahed.sarker.ietf@gmail.com>
Date: Thu, 23 May 2024 16:36:26 +0200
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To: Sergio Garcia Murillo <sergio.garcia.murillo@gmail.com>
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Subject: [Wish] Re: Zaheduzzaman Sarker's Discuss on draft-ietf-wish-whip-14: (with DISCUSS and COMMENT)
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On Thu, May 23, 2024 at 1:42 PM Sergio Garcia Murillo <
sergio.garcia.murillo@gmail.com> wrote:

>
>
> On Thu, May 23, 2024 at 11:50 AM Zaheduzzaman Sarker <
> zahed.sarker.ietf@gmail.com> wrote:
>
>>
>>
>> On Mon, May 20, 2024 at 4:02 PM Sergio Garcia Murillo <
>> sergio.garcia.murillo@gmail.com> wrote:
>>
>>> Hi Zahed, thank you very much for your review and comments, please check
>>> inline
>>>
>>> On Thu, May 16, 2024 at 3:52 PM Zaheduzzaman Sarker via Datatracker <
>>> noreply@ietf.org> wrote:
>>>
>>>> ----------------------------------------------------------------------
>>>> DISCUSS:
>>>> ----------------------------------------------------------------------
>>>>
>>>> Thanks for working on this specification. Thanks to Bernard Aboba for
>>>> his
>>>> TSVART review.
>>>>
>>>> I would like to discuss two points -
>>>>
>>>> 1. Rate adaption considerations when using WebRTC for ingest: as
>>>> pointed out by
>>>> the TSVART reviewer, the existing congestion control used in the WebRTC
>>>> libraries is not suitable for streaming, hence, need special
>>>> considerations to
>>>> be used as it is. I was expecting at least some considerations or
>>>> warnings in
>>>> the section 4.2.
>>>>
>>>
>>> While Congestion Control is one of my favorite topics, WebRTC does not
>>> specify much in that regard (
>>> https://www.rfc-editor.org/rfc/rfc8834.html#section-7). So IMO, talking
>>> about existing CC and BWE algorithms in WebRTC libraries is more suited for
>>> as an implementation guideline and not part of the specification. Up to now
>>> we have avoided including that kind of implementation guidelines in the RFC.
>>>
>>
>> I don't think we need to describe existing CC or BWE algorithms in this
>> specification. There are existing CC algorithms tested and implemented for
>> WebRTC communication based on the guidance available in RFC8834. However,
>> WebRTC was not directly designed for ingest of streaming media and as
>> mentioned CC requirement (https://www.rfc-editor.org/info/rfc8836) in
>> RFC 8834 does not include streaming considerations. Hence, what we can
>> simply say one need to consider the use of existing WebRTC CC algorithms
>> and those might not be sufficient for the ingest use case covered in this
>> specification. If we have more details - we can very well add them. As this
>> document stands it does not talk about changes required in CC
>> considerations at all.
>>
>
> While I don't mind adding some non-normative text, I have been fighting
> against FUD on werbtc usage on streaming for so long that I would strongly
> oppose adding any ill-defined, negative tone description not fully backed
> by technical facts.
> In that regard, one of the WHIP goals is (as stated in the introduction):
>
> *Enables ingestion on both traditional media platforms and WebRTC
> end-to-end platforms, achieving the lowest possible latency.*
>
>
I would note the implication of "not achieving lowest possible latency" is
not clear in this specification while ingest is usually a case to highest
throughput. So, which one is the primary goal here? - my guess is - it is
about achieving lowest possible latency while achieving highest possible
throughput. None of the webrtc implementations I know of focuses on highest
throughput when it comes to congestion and rate control - if you are saying
I can take any webrtc implementation ( say libwebrtc which implements a
congestion control algorithm) and establish signaling with WHIP for ingest
case and it would simple work, then we would actually need "fully backed by
technical facts" regarding that.


> This matches perfectly with the requirements in RFC 8834:
>
> *These algorithms have also been used for transfer of media streams that
> are viewed in a non-interactive manner, such as "streaming" video, where
> having the data ready when the viewer wants it is important, but the exact
> timing of the delivery is not.*
>
> *When handling real-time interactive media, the requirements are
> different. One needs to provide the data continuously, within a very
> limited time window (no more delay than hundreds of milliseconds
> end-to-end).*
> *The congestion control algorithm MUST attempt to provide
> as-low-as-possible-delay transit for interactive real-time traffic while
> still providing a useful amount of bandwidth.*
>
>
Where is this stated?


>
> If the latency budget is higher (in the range of 1s), then different
> congestion control/bwe could be implemented, although we would be moving
> out of the original scope of WHIP.
>

So WHIP has a latency scope, beyond which this might not be usable. I
haven't noted such scope this specification. It seems to me very important
to state such latency range.

>
>
>>
>>>
>>>
>>>>
>>>> 2. As HTTP proxying is common, why should this specification not have
>>>> any
>>>> discussion on WHIP client behind a proxy. I am assuming it does not
>>>> change much
>>>> but I was at least expecting some considerations for such a scenario.
>>>
>>>
>>> We have been advised by the  HTTP directorate review to avoid
>>> re-specifying HTTP and not include text that is already covered by the HTTP
>>> RFCs. In that regard, if the WHIP client/server are not required to have
>>> any special consideration when working with proxying, I would prefer not to
>>> include any reference at all.
>>>
>>
>> Yes, I would also advice not to re-specify HTTP :-).  That also means we
>> need to consider when the WHIP client is behind a proxy then how the ICE
>> works between media server and the WHIP client. As there was no mention of
>> WHIP client behind a HTTP proxy case hence the discuss was to make sure we
>> have considered the case and decided no special considerations would
>> require for WHIP to function. I believe it would great if we actually
>> record this in the specification explicitly.
>>
>
> An HTTP proxy won't affect ICE in any means, just the HTTP POST carrying
> the SDP O/A. If there is a gateway blocking/filtering UDP traffic, then
> that's exactly what ICE is designed for and I don't feel we need to add any
> further note about it.
>

I think if this specification says, WHIP is fully compliant with
https://www.rfc-editor.org/rfc/rfc9110.html#name-terminology-and-core-concep
, then it will solve my concerns. This specification actually should say -
what is a "HTTP-based protocol" in this context?


>
>
>> .
>>
>>>
>>>
>>>>   # Figure 1 is also a bit confusing. The WHIP session is described as
>>>>   allocated http resources at WHIP endpoint, but draws WHIP session as
>>>>   something out of WHIP endpoint.
>>>>
>>>
>>> The whip sesion is an HTTP resource allocated BY the WHIP endpoint, not
>>> at the WHIP endpoint.
>>>
>>
>> OK, should we the consider the WHIP endpoint as the origin server
>> according to the section 9.3.3 of RFC 9110 ?
>>
>
> Yes, I think that would be correct. As I still have to answer the review
> of the HTTP directorate, I will add the question there so they can provide
> guidance.
>

Sounds good.


>
> Best regards
> Sergio
>
>>