[Starlink] FQ_Codel

[warren ponder]

So this is really helpful. Is it fair to say then that end users with SQM
and fq_codel on a Starlink connection should essentially not turn on
SQM.and.just leave it off?



On Wed, Jun 8, 2022, 11:47 AM David P. Reed <dpreed at deepplum.com> wrote:

> I'm just going to remind folks that fixing bufferbloat in Starlink won't
> be possible with FQ-Codel in the CPE equipment. If that were possible, it
> could be fixed entirely in a box sitting between the dishy and the user's
> "home network".
>
>
>
> Evidence exists that the bulk of the "bloat" can exist, not just in the
> dishy, but also in the central "access point" where satellites in a
> coverage region direct all the traffic from and to the public Internet.
> This connection from the region becomes bloated if the inbound link and
> outbound link become "underprovisioned" for peak rates of all the served
> dishy terminals.
>
> That public-Internet to StarLink access point (is there a more distinct,
> precise name) can develop a very long delay queue.  For the same reason
> that bufferbloat always gets designed in - memory is cheap and plentiful,
> so instead of dropping packets to minimize latency, the link just stores
> packets until multiple seconds worth of traffic build up on one or both
> ends of that link.
>
>
>
> This problem can be solved only by dropping packets (with packet drop rate
> mitigated by ECN-marking) to match the desired round-trip latency across
> the entire Internet. Typically, this queue size should max out and start
> dropping packets at about 2 * cross-Internet desired latency * bit-rate of
> this link.
>
> Cross-Internet desired latency can be selected these days by using
> light-speed in fiber between one side of the North American continent and
> the other - around 15 msec. is appropriate. (which should be the worst case
> end-to-end latency observed using Starlink, and is around the 20 msec.
> number bandied about by Musk - though he really never understood what
> end-to-end latency means).
>
>
>
>
>
> Now it may be that the dishy itself also has such bloat built in, which
> would make FQ-Codel in the dishy also important.
>
>
>
> The problem called bufferbloat occurs whenever ANY router on ANY
> end-to-end shared path allows such queueing delay to accumulate before
> shortening the queue.
>
>
>
> It really frustrates me that memory keeps being added to router outbound
> buffers anywhere. And it may be that the reason is that almost nobody who
> designs packet forwarding systems understands Queueing Theory at all! It
> certainly doesn't help that "packet drops" (even one or two per second) are
> considered a failure of the equipment.
>
>
>
> FQ-codel is great, but why it works is that it makes the choice of what
> packet to drop far better (by being fair and a little bit elastic).
> However, the lack of FQ-Codel doesn't fix system-level bufferbloat.
>
>
>
>
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