Re: [Bloat] FW: [Dewayne-Net] Ajit Pai caves to SpaceX but is still skeptical of Musk's latency claims

[David Lang <david@lang.hm>]

On Fri, 12 Jun 2020, Michael Richardson wrote:

> David Lang <david@lang.hm> wrote:
>    > my point is that the if the satellite links are not the bottleneck, no
>    > queuing will happen there.
>
> It's a mesh of satellites.
>
> If you build it into a DODAG (RFC6550 would work well), then you will either
> a bottleneck at the top of tree (where the downlink to the DC is), or you
> will have significant under utilitization at the edges, which might encourage
> them to buffer.
>
> Now, the satellites are always moving, so which satellite is next to the DC
> will change, and this quite possibly could be exploited such that it's
> always a different buffer that you bloat, so the accumulated backlog that
> David P spoke about in his message might get to drain.
>
> But, the right way to use this mesh is, in my opinion, to have a lot of
> downlinks, and ideally, to do as much e2e connection as possible.
> Don't connect *to* the Internet, *become* an Internet.
> That is, routing in the satellite mesh, not just creation of circuits to DCs.

realistically, the vast majority of the people who have the mobile endpoints are 
going to be talking to standard websites and services, and those are going to be 
on the Internet, not on starlink nodes.

'normal' traffic is highly asymmetric, but the radio links do not seem to be, so 
you can have a lot of mobile units talking to the Internet on a smallish number 
of downlinks without having a bottleneck in the 'upstream' direction from the 
mobile units.

it's the replies that are far more likely to be a problem (the 'downlink' 
direction as far as the user is concerned), but they don't have to do anything 
super special there, if they just turn on fq_codel on the uplink routers between 
the Internet and the satellites, it will do a good job of managing that link.

Is it possible to saturate that and run into grief? sure. It's possible to 
oversubscribe any service. But it's also possible to run a service without 
oversubscribing it.

> Anything less, and it's just a faster Iridium.
>
>    > I expect the queuing to happen at the internet-satellite gateways, which is
>    > much more conventional software and if they do something sane at the gateways
>    > it will address the problem for pretty much everyone. They don't have to
>    > implement anything special on the satellites.
>
>    > and if he is promising good latency, but there isn't good latency, it isn't
>    > going to be swept under the rug the way incumbant ISPs were able to.
>
> I would expect to use SDN to create virtual satellites which appear to be
> "stationary", and then do routing on top of that.

I expect that it will be more dynamic than that. given that there could be 
mobile stations anywhere, creating virtual satellites is going to be a poor 
choice for many locations. I expect it will be something along the lines of each 
satellite has a ongoing broadcast of how busy it is and the ground stations send 
based on this.

do I expect them to get it right immediately? no.

but SpaceX has a need for good communication in odd areas (like their recovery 
ships and their spacecraft), so when they do run into grief, I expect them to 
fix the problem fairly quickly, not pretend it isn't there.

Remember, Musk already sacked the starlink leadership once for being to stuck in 
'the way satellites are always built' so if it doesn't work well under load and 
they can't fix it, he will find people who can.

David Lang