D&C Lug - Home Page
Devon & Cornwall Linux Users' Group

[ Date Index ][ Thread Index ]
[ <= Previous by date / thread ] [ Next by date / thread => ]

Re: [LUG] ADSL in Cornwall (Again!)



Philip Dore wrote:

ADSL via Satelite is now available countrywide, it's a bit more expensive
than via the phone line - take a look at
http://www.btopenworld.com/satellite/.

It is just BT reselling an existing VSAT satellite product, it
isn't anything new. I dare say BT probably get a good bulk
discount.

It is broadband nor ADSL of course.

The problem with satellites is latency. 

The satellites are geostationary, so the signal must travel
about 45,000 miles before they are put into the usual optical
fibre network. Even at the speed of light this means you will
get half a second of latency per round trip just going to the
satellite and back twice, even a simple web pages retrieval can
easily require 3 or 4 round trips (Many require more, but web
browsers are multithreaded, so they will probably happen
concurrently after the first few) - do the maths - that is 2
seconds per web pages on top of any other delays.

Fine for watching movies, or listening to Internet radio
stations, or even downloading Linux distros, but conferencing is
going to be unpleasant, and even normal surfing may be painfully
slow.

For normal broadband requirements in rural areas you want
wireless ground to ground systems, or at worst bouncing signals
of the Ionosphere, or polar orbiting satellites. 

Better still for many sites would be if BT enabled ADSL for
those exchanges that have enough people that assuming a decent
take up rate 20% of households, would be economically viable.

If it is so fast why don't BT quote comparitive time to download
a well known web page - I'd even settle for www.microsoft.com ?

More bizarre is BT don't quote a contention ratio figure for the
service.

 Simon


-- 
"Don't get me started on intuitive. You know what's intuitive?
Fear of heights. Everything else we call intuitive, such as
walking or using a pencil took years of practice." - Don Norman

--
The Mailing List for the Devon & Cornwall LUG
Mail majordomo@xxxxxxxxxxxx with "unsubscribe list" in the
message body to unsubscribe.


Lynx friendly