Re: [Mops] Reminder: Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC

["Holland, Jake" <[e-mail]>]

Hi Anna,

(And replacing Nathalie’s email with the correct one, hopefully)

That was not quite my understanding, no.  Sorry if I opened this discussion poorly.  In Nathalie’s initial response, she clarified that it’s configurable, including the option to disable the reordering buffer.

However, I understood this as an option available to the service provider operating the MP-DCCP split path proxies that tunnel the carried traffic, not necessarily to the endpoints or the applications having their traffic split.

Depending on how it’s deployed, this may or may not be a problem for particular endpoints, but I couldn’t tell if there was an obvious or easy way for an application to select the use case (particularly one that is just trying to use QUIC and transparently getting traffic-splitting delivery) in a way that the operator will understand, so I thought it best to raise the point for discussion.

Best,
Jake

From: Anna Brunström <[e-mail]>
Date: Wed,2021-07-28 at 5:31 PM
To: Matt Joras <[e-mail]>, "Holland, Jake" <[e-mail]>
Cc: David Schinazi <[e-mail]>, Roberto Peon <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, Ian Swett <[e-mail]>, "[e-mail]" <[e-mail]>, "Das, Dibakar" <[e-mail]>, Alan Frindell <[e-mail]>, "[e-mail]" <[e-mail]>, Kirill Pugin <[e-mail]>
Subject: RE: [Mops] Reminder: Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC

I think multipath and L2 are a bit different as multipath may lead to large amounts of reordering and delay variations. Not all applications/implementations may handle this well. But you should of course also have the possibility to just pass the packets on, and I agree that in many cases this will be the best.

In the context of MP-DCCP, both scheduling and reordering are modular components so you can certainly choose to pass the packets on without delay. The need for supporting this is also stated in the draft. But for the multipath case, I think it is useful to also have the ability to reduce reordering if needed. For ATSSS I guess weather that is desirable or not may be controlled by the selected mode.

@Jake: if you understood our conversation in ANRW as suggesting that MP-DCCP should always reorder, that was a misunderstanding.

Best,
Anna


From: Matt Joras <[e-mail]>
Sent: den 29 juli 2021 01:58
To: Holland, Jake <jholland=[e-mail]>
Cc: David Schinazi <[e-mail]>; Roberto Peon <[e-mail]>; Anna Brunström <[e-mail]>; [e-mail]; [e-mail]; Ian Swett <[e-mail]>; [e-mail]; Das, Dibakar <[e-mail]>; Alan Frindell <[e-mail]>; [e-mail]; Kirill Pugin <[e-mail]>
Subject: Re: [Mops] Reminder: Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC

Speaking as an individual, a couple comments inline adding to what Jake is saying.

On Wed, Jul 28, 2021 at 3:58 PM Holland, Jake <jholland=[e-mail]<mailto:[e-mail]>> wrote:
And yet, we still can see network buffering to maintain packet ordering in new work today, including work specifically targeted at QUIC.

In the “CCID5” ANRW talk from Monday’s 2nd session, a reordering buffer was mentioned in the transparent proxy for the MP-DCCP tunnel they’re wrapping QUIC packets in to get multipath traffic-splitting during transport within wireless carriers (a proposal coming soon to tsvwg):
https://irtf.org/anrw/2021/program.html#:~:text=nathalie%20romo%20moreno<https://urldefense.com/v3/__https:/irtf.org/anrw/2021/program.html*:*:text=nathalie*20romo*20moreno__;I34lJQ!!GjvTz_vk!AVpyqSAj3HYNjnpUTryB_6DdElZmzNy4D78JApMaTuSanBUHBhhvFtmh1HJdILQ$>

I asked specifically about the reordering buffer at the mic, since this kind of thing has made me sad before. (There was also a side discussion in the chat.)  I got the impression they believe they’re seeing some benefits to apps by including this reordering buffer in the network, citing the wider range of reordering that you get for split-path transport (as compared to the L2 forwarding case).

I would question whether any application-level benefits could be measured by the network intermediaries. We (i.e., endpoint owners) have a hard enough time surmising application-level improvements from _endpoint_ transport metrics, let alone trying to intuit those as a network intermediary without any application context whatsoever. Making network-level decisions based on limited information is a recipe for "optimizations" that seem good on paper and for a limited set of metrics but are worse in reality. This is exactly the kind of thing that has led to the proliferation of TCP session terminating PEPs, which have overall been a real impedance to making improvements with TCP on the Internet.


If there’s endpoint implementations that aren’t doing a good enough job here and therefore we’re seeing new network deployments that introduce buffering because their measurements indicate it’s helpful on common use cases, it could be worthwhile to get this straightened out before it gets too normalized and we start having networks reintroduce hol-blocking in a way that hurts some QUIC use cases in the name of helping others.

Although I expect this can and should be solved at the endpoints, if there is data showing that the ordering solves a real problem with current implementations, reasonable people can reasonably conclude that network buffering to maintain packet order is a good idea.

(Note: UDP client-side port might be an option for a network-visible signal that might “just work” for many (hopefully most?) ordering schemes to avoid buffering for ordering, but it might need some API support and it might lead to some other kinds of ugly nat problems if there’s too many flows doing it...)

+Anna, Nathalie and Markus.  Hopefully they can comment on this also.

Best,
Jake

From: David Schinazi <[e-mail]<mailto:[e-mail]>>
Date: Wed,2021-07-28 at 2:16 PM
To: Roberto Peon <[e-mail]<mailto:[e-mail]>>
Cc: Ian Swett <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "Das, Dibakar" <[e-mail]<mailto:[e-mail]>>, Alan Frindell <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, Kirill Pugin <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Mops] Reminder: Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC

Why would we need a signal here? This applies to all traffic, be it TCP QUIC or anything else. Firmwares introducing latency to reorder packets was a reaction to bad implementations of TCP from a long time ago that have been fixed in systems that care about performance. In today's world, L2 is better off delivering any and all packets in the order they arrive instead of introducing buffer bloat.

David

On Wed, Jul 28, 2021 at 1:24 PM Roberto Peon <fenix=[e-mail]<mailto:[e-mail]>> wrote:
The ideal would be to have public bits that were intended to be interpreted by (as you say, visible to) those layers so any L2 could adapted appropriately without reinventing the wheel.
It isn’t just the local radio firmware that one needs to worry about—it is also the basestation(s) that may be “helping”.

Separately, but also important, is being able to get signals from the application about what tradeoffs should be at the network. I believe that this dovetails into many of the multipath issues, btw.

A couple potentially interesting params are:
  A bit to say please don’t HoL block
  Some kind of mechanism(s) to bound retries (e.g. “don’t retry bit”, but that is obviously not as expressive as throw out packet older than X microseconds)

-=R

From: QUIC <[e-mail]<mailto:[e-mail]>> on behalf of Ian Swett <ianswett=[e-mail]<mailto:[e-mail]>>
Date: Wednesday, July 28, 2021 at 12:42 PM
To: "Das, Dibakar" <[e-mail]<mailto:[e-mail]>>
Cc: Alan Frindell <afrind=[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, Kirill Pugin <[e-mail]<mailto:[e-mail]>>
Subject: Re: Reminder: Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC

Hi,

I can't answer for Alan, but my belief is yes.  Client wifi stacks sometimes also do some reordering(and introduce the corresponding latency), so if we could design an indication that in-order delivery has no value, it could be fairly widely applicable.

That being said, I don't know what the right mechanism is?  Would we need something visible to a network or can we get away with a socket option that propagates to the local 5G network or Wifi firmware when possible?

Ian

On Wed, Jul 28, 2021 at 3:15 PM Das, Dibakar <[e-mail]<mailto:[e-mail]>> wrote:
Hi Kirill, Alan,

I could not attend the call this week and wont be able to attend this side meeting either.

But I had a general question about the performance of all such QUIC based protocols over wireless. Typically, the 5G and WiFI MAC layers deliver frames in-order which sort of recreates the HOL blocking problem at lower layers. I would expect this to in turn prevent the QUIC protocol to achieve its full performance gains at least in some congested network scenarios. Considering that in-order delivery is made optional in 5G PDCP, I was wondering if there could be a value to have some signaling defined in the QUIC (or RUSH ?) protocol that would allow lower layers to make better decision about whether to enable/disable in-order delivery for certain streams.

I apologize in advance if this is not the right venue to ask questions.

Regards,
Dibakar



From: QUIC <[e-mail]<mailto:[e-mail]>> On Behalf Of Alan Frindell
Sent: Wednesday, July 28, 2021 8:42 AM
To: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; QUIC WG <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: Kirill Pugin <[e-mail]<mailto:[e-mail]>>
Subject: Reminder: Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC

Video Ingest over QUIC Side Meeting Friday 7/30 18:00 UTC / 11 Pacific

Link to draft agenda and video conference details: https://github.com/afrind/draft-rush/blob/main/meeting-materials/agenda.2021.07.03.md<https://urldefense.com/v3/__https:/github.com/afrind/draft-rush/blob/main/meeting-materials/agenda.2021.07.03.md__;!!GjvTz_vk!E0SzSsjcIQqc-TDdIf5-y7XjoWfnEA-7r9fdRAjEKZXc1GYhGomlKIXMwmDZ0Ls$>

-Alan

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