I don't believe what you wrote is 100% true. What can happen with copper
pairs is that interference (water, squirrels chewing, corrosion, etc.)
or "noise" causes damaged and or dropped packets, and these create
requests for re-sends of those packets. So your "throughput" in terms of
packets per second goes down, which is interpreted by the measurement
applications as reduced "line speed". It should also be noted the the
other limitation of Internet access service is dependent on the "pipe"
from the service provider to the nearest DNS server - if all they have
is a link capable of say 10 Mb/sec, then no matter what facilities you
have, you will be sharing that pipe with the other subscribers, whether
that is cable, DSL, or FIOS. Small rural telephone companies can offer
DSL relatively cheaply, but if they don't have a hefty link to the
Internet, you aren't going to get blinding speed, especially after
school, weekends, and on snow days.
As far as distance from the central office, you are correct that there
is a limit on the length of the copper than will work, but that can be
extended by the use of fiber from the central office to a repeater,
extending the distance considerably. In my case, I am 8 miles from the
serving central office and still have ADSL that works about 1.8 Mb/sec
down and about half that up. Verizon placed a repeater hut about two
miles from my place, and it serves a LOT of subscribers in the area - we
don't have cable, so anything is better than dial-up. Verizon is also
putting in fiber to replace copper in a lot of New Jersey towns, but
where we live won't be done until last - we don't have enough
subscribers in this rural area to make it worth the expense.
Mike
Eric S. Sande wrote:
Most people I know with DSL find fairly constanct rates. But I know
a few
who apparently have some sort of issues with the copper wire from the
CO to
the house. Rain can really lower their data rate.
Yep. The primary limitation of "DSL" is line loss. If I am the
provider, I
can set your "cap" at 3 mbps (for example) at the point of presence (POP).
But the ultimate arbiters of your speed are going to be determined by loop
quality. If you have a crappy loop to begin with, or if you are a long
distance
from the POP, you aren't going to get 3 mbps.
When it rains, with aerial cable, some things in the system sometimes,
well,
leak. Mostly the telco has this under control. Sometimes it doesn't.
A telco won't sell DSL to a subscriber beyond 18K feet from the POP.
If they do they're behaving irresponsibly, because the physical limitations
of the network are such that it can't be supported with any reasonable
QOS at that distance, even with a perfect loop (which exists only in OZ).
I have one question for Paula. Are you in Verizon territory?
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