Re: [iccrg] Will Fair Queuing change Congestion Control?

Hello Max,

Few things to note, FQ expands to Flow Queue (not fair queueing) which means every flow (4 tuple) has a different queue. Priorities are implemented based on service classes, for example. Also, Apple devices are not the most common bottleneck on an end to end path.

Even if we assume there is enough deployment of flow queueing in the network, flows can hurt themselves by not responding to growing latency. This problem has been addressed in L4S drafts and I highly recommend reading them. ECN combined with an immediate AQM combined with Prague congestion control is basically the idea of L4S.

Vidhi

> On Jan 3, 2023, at 9:20 AM, Maximilian Bachl <maximilian.bachl@gmail.com> wrote:
> 
> Apple introduced fair queuing (FQ) on more than a billion of devices in the last years (https://blog.cerowrt.org/post/state_of_fq_codel/). I wonder if this could have an impact on congestion control. When there’s fair queuing at the bottleneck link of a path, the endpoints can use delay-minimizing congestion control and don’t have to worry about more aggressive senders. 
> 
> However, currently, there’s no established mechanism for endpoints to know of the existence of fair queuing on a path. There are some possibilities, though, how endpoints can be made aware of the existence of fair queuing: 
> A dedicated bit in some packet header. For example, some ECN or DSCP bits could be repurposed to indicate the existence of fair queuing at the bottleneck. Drawback: It’s hard to convince people to repurpose/introduce new bits and switches/routers have to support it. 
> An end-host-based mechanism to detect fair queuing without the involvement of switches/routers. I created a proof-of-concept implementation of such a mechanism, which can detect the presence/absence of fair queuing with an accuracy of > 95% (https://arxiv.org/abs/2206.10561).
> Closed ecosystems in which all components are aware that there is fair queuing: As a hypothetical example, let’s assume a user plays a game on nvidia’s cloud-gaming platform on an iPhone. The phone is connected to T-Mobile’s 5G network. Both the client on the iPhone as well as the server in nvidia’s network know that there’s fair queuing on the path between the client and the server, since they have an agreement with T-Mobile, which controls the entire path. No extra bits in packet headers are needed, just mutual agreement between the user’s device, the cellular network provider as well as the server on the internet. 
> 
> If you have some opinions on whether fair queuing is going to change how we do congestion control, I’d be curious. 
> 
> Regards,
> Max
> _______________________________________________
> iccrg mailing list
> iccrg@irtf.org
> https://www.irtf.org/mailman/listinfo/iccrg