[Starlink] Starlink and bufferbloat status?

Fri Jul 16 17:40:15 EDT 2021

If we understand shell as “group of satellites at a certain altitude range”, there is not much point in linking between shells if you can link within one shell and orbital plane, and that plane has at least one satellite within range of a gateway. I could be proven wrong, but IMHO the first generation of links are meant of intra-plane, and maybe at a stretch cross-plane to the next plane East or West.

The only way to eventually go is optical links to the ground too, as RF will only get you so far. At that stage, every shell will have its own optical links to the ground, with gateways placed in areas with little average cloud cover.

Best,

Mike
On Jul 16, 2021, 23:30 +0200, David Lang <david at lang.hm>, wrote:
> at satellite distances, you need to adjust your vertical direction depending on
> how far away the satellite you are talking to is, even if it's at the same
> altitude
>
> the difference between shells that are only a few KM apart is less than the
> angles that you could need to satellites in the same shell further away.
>
> David Lang
>
> On Fri, 16 Jul 2021, Mike Puchol wrote:
>
> > Date: Fri, 16 Jul 2021 22:57:14 +0200
> > From: Mike Puchol <mike at starlink.sx>
> > To: David Lang <david at lang.hm>
> > Cc: Nathan Owens <nathan at nathan.io>,
> > "starlink at lists.bufferbloat.net" <starlink at lists.bufferbloat.net>,
> > David P. Reed <dpreed at deepplum.com>
> > Subject: Re: [Starlink] Starlink and bufferbloat status?
> >
> > Correct. A mirror tracking head that turns around the perpendicular to the satellite path allows you to track satellites in the same plane, in front or behind, when they change altitude by a few kilometers as part of orbital adjustments or collision avoidance. To have a fully gimbaled head that can track any satellite in any direction (and at any relative velocity!) is a totally different problem. I could see satellites linked to the next longitudinal plane apart from those on the same plane, but cross-plane when one is ascending and the other descending is way harder. The next shells will be at lower altitudes, around 300-350km, and they have also stated they want to go for higher shells at 1000+ km.
> >
> > Best,
> >
> > Mike
> > On Jul 16, 2021, 20:48 +0200, David Lang <david at lang.hm>, wrote:
> > > I expect the lasers to have 2d gimbles, which lets them track most things in
> > > their field of view. Remember that Starlink has compressed their orbital planes,
> > > they are going to be running almost everything in the 550km range (500-600km
> > > IIRC) and have almost entirely eliminated the ~1000km planes
> > >
> > > David Lang
> > >
> > > On Fri, 16 Jul 2021,
> > > Mike Puchol wrote:
> > >
> > > > Date: Fri, 16 Jul 2021 19:42:55 +0200
> > > > From: Mike Puchol <mike at starlink.sx>
> > > > To: David Lang <david at lang.hm>
> > > > Cc: Nathan Owens <nathan at nathan.io>,
> > > > "starlink at lists.bufferbloat.net" <starlink at lists.bufferbloat.net>,
> > > > David P. Reed <dpreed at deepplum.com>
> > > > Subject: Re: [Starlink] Starlink and bufferbloat status?
> > > >
> > > > True, but we are then assuming that the optical links are a mesh between satellites in the same plane, plus between planes. From an engineering problem point of view, keeping optical links in-plane only makes the system extremely simpler (no full FOV gimbals with the optical train in them, for example), and it solves the issue, as it is highly likely that at least one satellite in any given plane will be within reach of a gateway.
> > > >
> > > > Routing to an arbitrary gateway may involve passing via intermediate gateways, ground segments, and even using terminals as a hopping point.
> > > >
> > > > Best,
> > > >
> > > > Mike
> > > > On Jul 16, 2021, 19:38 +0200, David Lang <david at lang.hm>, wrote:
> > > > > the speed of light in a vaccum is significantly better than the speed of light
> > > > > in fiber, so if you are doing a cross country hop, terminal -> sat -> sat -> sat
> > > > > -> ground station (especially if the ground station is in the target datacenter)
> > > > > can be faster than terminal -> sat -> ground station -> cross-country fiber,
> > > > > even accounting for the longer distance at 550km altitude than at ground level.
> > > > >
> > > > > This has interesting implications for supplementing/replacing undersea cables as
> > > > > the sats over the ocean are not going to be heavily used, dedicated ground
> > > > > stations could be setup that use sats further offshore than normal (and are
> > > > > shielded from sats over land) to leverage the system without interfering
> > > > > significantly with more 'traditional' uses
> > > > >
> > > > > David Lang
> > > > >
> > > > > On Fri, 16 Jul 2021, Mike Puchol wrote:
> > > > >
> > > > > > Date: Fri, 16 Jul 2021 19:31:37 +0200
> > > > > > From: Mike Puchol <mike at starlink.sx>
> > > > > > To: David Lang <david at lang.hm>, Nathan Owens <nathan at nathan.io>
> > > > > > Cc: "starlink at lists.bufferbloat.net" <starlink at lists.bufferbloat.net>,
> > > > > > David P. Reed <dpreed at deepplum.com>
> > > > > > Subject: Re: [Starlink] Starlink and bufferbloat status?
> > > > > >
> > > > > > Satellite optical links are useful to extend coverage to areas where you don’t have gateways - thus, they will introduce additional latency compared to two space segment hops (terminal to satellite -> satellite to gateway). If you have terminal to satellite, two optical hops, then final satellite to gateway, you will have more latency, not less.
> > > > > >
> > > > > > We are being “sold” optical links for what they are not IMHO.
> > > > > >
> > > > > > Best,
> > > > > >
> > > > > > Mike
> > > > > > On Jul 16, 2021, 19:29 +0200, Nathan Owens <nathan at nathan.io>, wrote:
> > > > > > > > As there are more satellites, the up down time will get closer to 4-5ms rather then the ~7ms you list
> > > > > > >
> > > > > > > Possibly, if you do steering to always jump to the lowest latency satellite.
> > > > > > >
> > > > > > > > with laser relays in orbit, and terminal to terminal routing in orbit, there is the potential for the theoretical minimum to tend lower
> > > > > > > Maybe for certain users really in the middle of nowhere, but I did the best-case math for "bent pipe" in Seattle area, which is as good as it gets.
> > > > > > >
> > > > > > > > On Fri, Jul 16, 2021 at 10:24 AM David Lang <david at lang.hm> wrote:
> > > > > > > > > hey, it's a good attitude to have :-)
> > > > > > > > >
> > > > > > > > > Elon tends to set 'impossible' goals, miss the timeline a bit, and come very
> > > > > > > > > close to the goal, if not exceed it.
> > > > > > > > >
> > > > > > > > > As there are more staellites, the up down time will get closer to 4-5ms rather
> > > > > > > > > then the ~7ms you list, and with laser relays in orbit, and terminal to terminal
> > > > > > > > > routing in orbit, there is the potential for the theoretical minimum to tend
> > > > > > > > > lower, giving some headroom for other overhead but still being in the 20ms
> > > > > > > > > range.
> > > > > > > > >
> > > > > > > > > David Lang
> > > > > > > > >
> > > > > > > > >   On Fri, 16 Jul 2021, Nathan Owens wrote:
> > > > > > > > >
> > > > > > > > > > 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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