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back to article EU sets out mobile satellite services

The European Parliament has approved a proposal that demands mobile satellite services reach at least 60 per cent of every country in Europe, and 50 per cent of their populations, in order to get operating spectrum. The ruling relates to a couple of chunks of spectrum which have been handed to the EU by member countries, for …

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Several-second latency

Huh? I'm no physicist, but given c=3x10^9m/s then round-trip time is around 23ms. Presumably there will be switching delays, but several *seconds*? Are they writing out the packets by hand?

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Coat

Bugger.

OK, so I was off by a factor of 10, and it's 230ms rtt. But still, hardly several seconds.

Mine's the one with the F in physics.

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A little knowledge

It's the RTT: up and down then up and down back. 22,500 miles / 45,000 km approx x 4.

More the further north or south of equator you are and more the further east or west of due south to yourself the oribital slot is.

Closer to 860ms

even then, a web page involves ARP, DNS, TCP handshakes etc, making delays upto 4000ms. So VSAT modems cheat. TCP/IP packets are acknowleged at both end and resent between the hub & terminal if a problem. Also ARP and DNS tables etc cached.

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RTT

on web browsing nothing at all happens for about 900ms when you click a link. Then "Bang" the whole page appears.

VOIP is a bit easier if you take turns like two way radio. GSM to GSM or 3G can

actually have nearly as big delays.

real life 3G/HSDPA is 120ms MINIMUM and up to 1000ms + with none of the tricks of VSAT. So around 200ms to 400ms page load times can be 4x worse than satellite even though the raw download speed is the same.

It's also easier to get a better speed down & up more consistent on Satellite than HSDPA (70kbps when 24 users in a sector).

VOIP is generally worse on EDGE/EVDO/3G/HSDPA than Satellite!

Don't even think of online gaming FPS etc on 3G!

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Ever tried it?

I used an Inmarsat BGAN geostationary on a trip across the Sahara earlier this year. You might not want to do FPS shooters or streaming full-screen video on it (bandwidth is limited unles you buy dedicated streaming services) but for regular browsing, email and the other run-of-the-mill internet stuff practised by non-Reg folks, it was pretty sweet. And VOIP quality was not only very high but surprisingly low-latency.

A little real world experience is worth a lot more than calculating theoretical delay times.

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