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

[Roland Bless]

Hi Jonathan.

On 11.06.20 at 18:14 Jonathan Morton wrote:
>> On 11 Jun, 2020, at 7:03 pm, David P. Reed <dpreed at deepplum.com> wrote:
>>
>> So, what do you think the latency (including bloat in the satellites) will be? My guess is > 2000 msec, based on the experience with Apple on ATT Wireless back when it was rolled out (at 10 am, in each of 5 cities I tested, repeatedly with smokeping, for 24 hour periods, the ATT Wireless access network experienced ping time grew to 2000 msec., and then to 4000 by mid day - true lag-under-load, with absolutely zero lost packets!)
>>  
>> I get that SpaceX is predicting low latency by estimating physical distance and perfect routing in their LEO constellation. Possibly it is feasible to achieve this if there is zero load over a fixed path. But networks aren't physical, though hardware designers seem to think they are.
>>  
>> Anyone know ANY reason to expect better from Musk's clown car parade?
> 
> Speaking strictly from a theoretical perspective, I don't see any reason why they shouldn't be able to offer latency that is "normally" below 100ms (to a regional PoP, not between two arbitrary points on the globe).  The satellites will be much closer to any given ground station than a GEO satellite, the latter typically adding 500ms to the path due mostly to physical distance.  All that is needed is to keep queue delays reasonably under control, and there's any number of AQMs that can help with that.  Clearly ATT Wireless did not perform any bufferbloat mitigation at all.
> 
> I have no insight or visibility into anything they're *actually* doing, though.  Can anyone dig up anything about that?

I think the claims about low latency are driven by lower _propagation_
delays. So for long enough distances it may be more efficient to route
up to a LEO-satellite, then use inter-satellite communication (there
is the saving due to faster light propagation in space than in fiber)
and eventually go down to earth again.
This was mainly described in Mark Handley's HotNets'18 paper here:
https://dl.acm.org/doi/10.1145/3286062.3286075
(see also http://nrg.cs.ucl.ac.uk/mjh/starlink/)

Another recent paper is here, discussing several deployment options:
Giacomo Giuliari, Tobias Klenze, Markus Legner, David Basin, Adrian
Perrig, and Ankit Singla. 2020. Internet backbones in space. SIGCOMM
Comput. Commun. Rev. 50, 1 (January 2020), 25–37.
https://dl.acm.org/doi/abs/10.1145/3390251.3390256
(Note, that there is an error in the results of Section 6.1 and Figure
2, the stretch factor was chosen by a factor of 1.5 too large; errata
is under submission).

However, queueing delay is not considered so far. Furthermore, one may
expect packet reordering due to changing inter-satellite routes etc.

Regards,
 Roland