[Starlink] Starlink and bufferbloat status?

Fri Jul 16 13:13:42 EDT 2021

Elon said "foolish packet routing" for things over 20ms! Which seems crazy
if you do some basic math:

   - Sat to User Terminal distance: 550-950km air/vacuum: 1.9 - 3.3ms
   - Sat to GW distance: 550-950km air/vacuum: 1.9 - 3.3ms
   - GW to PoP Distance: 50-800km fiber: 0.25 - 4ms
   - PoP to Internet Distance: 50km fiber: 0.25 - 0.5ms
   - Total one-way delay: 4.3 - 11.1ms
   - Theoretical minimum RTT: 8.6ms - 22.2ms, call it 15.4ms

This includes no transmission delay, queuing delay,
processing/fragmentation/reassembly/etc, and no time-division multiplexing.

On Fri, Jul 16, 2021 at 10:09 AM David Lang <david at lang.hm> wrote:

> I think it depends on if you are looking at datacenter-to-datacenter
> latency of
> home to remote datacenter latency :-)
>
> my rule of thumb for cross US ping time has been 80-100ms latency (but
> it's been
> a few years since I tested it).
>
> I note that an article I saw today said that Elon is saying that latency
> will
> improve significantly in the near future, that up/down latency is ~20ms
> and the
> additional delays pushing it to the 80ms range are 'stupid packet routing'
> problems that they are working on.
>
> If they are still in that level of optimization, it doesn't surprise me
> that
> they haven't really focused on the bufferbloat issue, they have more
> obvious
> stuff to fix first.
>
> David Lang
>
>
>   On Fri, 16 Jul 2021, Wheelock, Ian wrote:
>
> > Date: Fri, 16 Jul 2021 10:21:52 +0000
> > From: "Wheelock, Ian" <ian.wheelock at commscope.com>
> > To: David Lang <david at lang.hm>, David P. Reed <dpreed at deepplum.com>
> > Cc: "starlink at lists.bufferbloat.net" <starlink at lists.bufferbloat.net>
> > Subject: Re: [Starlink] Starlink and bufferbloat status?
> >
> > Hi David
> > In terms of the Latency that David (Reed) mentioned for California to
> Massachusetts of about 17ms over the public internet, it seems a bit faster
> than what I would expect. My own traceroute via my VDSL link shows 14ms
> just to get out of the operator network.
> >
> > https://www.wondernetwork.com  is a handy tool for checking geographic
> ping perf between cities, and it shows a min of about 66ms for pings
> between Boston and San Diego
> https://wondernetwork.com/pings/boston/San%20Diego (so about 33ms for
> 1-way transfer).
> >
> > Distance wise this is about 4,100 KM (2,500 M), and @2/3 speed of light
> (through a pure fibre link of that distance) the propagation time is just
> over 20ms. If the network equipment between the Boston and San Diego is
> factored in, with some buffering along the way, 33ms does seem quite
> reasonable over the 20ms for speed of light in fibre for that 1-way transfer
> >
> > -Ian Wheelock
> >
> > From: Starlink <starlink-bounces at lists.bufferbloat.net> on behalf of
> David Lang <david at lang.hm>
> > Date: Friday 9 July 2021 at 23:59
> > To: "David P. Reed" <dpreed at deepplum.com>
> > Cc: "starlink at lists.bufferbloat.net" <starlink at lists.bufferbloat.net>
> > Subject: Re: [Starlink] Starlink and bufferbloat status?
> >
> > IIRC, the definition of 'low latency' for the FCC was something like
> 100ms, and Musk was predicting <40ms. roughly competitive with landlines,
> and worlds better than geostationary satellite (and many
> > External (mailto:david at lang.hm)
> >
> https://shared.outlook.inky.com/report?id=Y29tbXNjb3BlL2lhbi53aGVlbG9ja0Bjb21tc2NvcGUuY29tL2I1MzFjZDA4OTZmMWI0Yzc5NzdiOTIzNmY3MTAzM2MxLzE2MjU4NzE1NDkuNjU=#key=19e8545676e28e577c813de83a4cf1dc
>  https://www.inky.com/banner-faq/  https://www.inky.com
> >
> > IIRC, the definition of 'low latency' for the FCC was something like
> 100ms, and
> > Musk was predicting <40ms.
> >
> > roughly competitive with landlines, and worlds better than geostationary
> > satellite (and many wireless ISPs)
> >
> > but when doing any serious testing of latency, you need to be wired to
> the
> > router, wifi introduces so much variability that it swamps the signal.
> >
> > David Lang
> >
> > On Fri, 9 Jul 2021, David P. Reed wrote:
> >
> >> Date: Fri, 9 Jul 2021 14:40:01 -0400 (EDT)
> >> From: David P. Reed <dpreed at deepplum.com>
> >> To: starlink at lists.bufferbloat.net
> >> Subject: [Starlink] Starlink and bufferbloat status?
> >>
> >>
> >> Early measurements of performance of Starlink have shown significant
> bufferbloat, as Dave Taht has shown.
> >>
> >> But...  Starlink is a moving target. The bufferbloat isn't a hardware
> issue, it should be completely manageable, starting by simple firmware
> changes inside the Starlink system itself. For example, implementing
> fq_codel so that bottleneck links just drop packets according to the Best
> Practices RFC,
> >>
> >> So I'm hoping this has improved since Dave's measurements. How much has
> it improved? What's the current maximum packet latency under full
> load,  Ive heard anecdotally that a friend of a friend gets 84 msec. *ping
> times under full load*, but he wasn't using flent or some other measurement
> tool of good quality that gives a true number.
> >>
> >> 84 msec is not great - it's marginal for Zoom quality experience (you
> want latencies significantly less than 100 msec. as a rule of thumb for
> teleconferencing quality). But it is better than Dave's measurements showed.
> >>
> >> Now Musk bragged that his network was "low latency" unlike other high
> speed services, which means low end-to-end latency.  That got him
> permission from the FCC to operate Starlink at all. His number was, I
> think, < 5 msec. 84 is a lot more than 5. (I didn't believe 5, because he
> probably meant just the time from the ground station to the terminal
> through the satellite. But I regularly get 17 msec. between California and
> Massachusetts over the public Internet)
> >>
> >> So 84 might be the current status. That would mean that someone at
> Srarlink might be paying some attention, but it is a long way from what
> Musk implied.
> >>
> >>
> >> PS: I forget the number of the RFC, but the number of packets queued on
> an egress link should be chosen by taking the hardware bottleneck
> throughput of any path, combined with an end-to-end Internet underlying
> delay of about 10 msec. to account for hops between source and destination.
> Lets say Starlink allocates 50 Mb/sec to each customer, packets are limited
> to 10,000 bits (1500 * 8), so the outbound queues should be limited to
> about 0.01 * 50,000,000 / 10,000, which comes out to about 250 packets from
> each terminal of buffering, total, in the path from terminal to public
> Internet, assuming the connection to the public Internet is not a problem.
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