Latency, TCP ACKs and upload needs

Jean-Francois Mezei jfmezei_nanog at
Wed Apr 20 15:26:03 UTC 2016

Thanks to all for the sanity check.

Always depressing when you think you may have a good argument but after
much reading, you find out you don't :-(

BTW, in case someone knows. With the recent "beam" satellites having a
lot of different focused antennas, how does the uplink work ?

Does all traffic pass through a central "switch" which then directs
packets to the approperiate antenna ?

Would a each beam directed at a served area be paired with its own
dedicated beam directed at ground station ? Or does the uplink from
ground station carry traffic for multiple beams and thus becomes the
bottleneck ?

(Xplornet bragged about its next satellite having 20gbps capacity, but
IF the uplink from ground station is also at 20gps and serves 5 beams
aimed at Canada, then on average each beam only gets 4gbps ?)

With regards to the "dream" of having 350 low orbit satellites covering
the globe for Internet, does anyone know how the uplink will be done?
Won't there be a bottleneck if in serving Canada's north, satellites
currently speeding over the region have to use satellite-to-satellite
links to carry information until it reaches a satellite that is over a
ground station in the south ?

or is it expected that ground stations will be built "near" each area to
be served ?

(Am trying to justify that satellite should be reserved for people truly
isolated and that Nunavut communities should get undersea fibre and work
need to start now because of long construction times during which
satellites will fall further back in terms of capacity needs).

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