[e2e] TCP in outer space

Courtney, Bill Bill.Courtney at trw.com
Tue Apr 10 14:01:31 PDT 2001


One of the problems with using non-GEO satellites is that
the topology of the constellation is changing. True,
it changes in a predictable way, but the changes will,
nonetheless, require network reconfiguration. With non-GEO
satellites, not only might the inter-satellite links
be breaking and making, but also the earth-space access 
links for each user will be continually changing. 

In addition, satellite coverage footprints in a 
constellation usually overlap, and for many 
constellations the overlaps are also in constant 
change. This means that uplink and downlink bandwidth 
allocations among the satellites will be subject to 
changing re-use constraints. This makes it difficult 
to ensure that users in any particular area on the 
ground will receive a constant amount of bandwidth. And
fluctuating access bandwidth leads to all sorts of
problems, as you can imagine.

These and other difficulties must be balanced against the
possibility that latency might be lowered with non-GEO
constellations. (I say "might," because some of the
non-GEO difficulties can be addressed at the cost
adding latency.) Non-GEO can be a bear!!


> -----Original Message-----
> From: David P. Reed [mailto:dpreed at reed.com]
> Sent: Tuesday, April 10, 2001 12:13 PM
> To: end2end-interest at postel.org
> Subject: RE: [e2e] TCP in outer space
> Well, I feel stupid.  The fact that we use geostationary 
> relays to get to 
> moving near earth targets was complete news to me.
> But it does indeed raise a question - since we have 12 happy 
> satellites 
> doing GPS, and an Iridium constellation essentially going to 
> waste, why not 
> use these LEO systems to build a better near-earth access 
> network?  Latency 
> and noise reduction would be significant - the only problem 
> is that those 
> satellites need more complex power systems.
> - David
> --------------------------------------------
> WWW Page: http://www.reed.com/dpr.html

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