Text 10127, 55 rader
Skriven 2005-08-03 00:46:07 av Gordon Huff (1:106/2000.0)
  Kommentar till text 10113 av JEAN PARROT (1:123/140)
Ärende: Re: DSL ?
=================
-=> JEAN PARROT wrote to JEFF GUERDAT <=-

On the off chance this isn't a troll .....



 JG> The speed of light (well, copper wire) remains but the quality of the
 JG> signal over relatively uncontrolled impedance wires is a problem.  The
 JG> original wires were useful for only voice frequencies while now we're
 JG> trying to pass many MB of data that can't afford to lose a bit here and
 JG> there.  As they upgrade the infrastructure things would get better (I
 JG> suspect) but that can take a long time...

True enough but doesn't speak to the problem. The speed at which an
electric wave propagates in a given medium is fairly constant. 
Signaling speed is something different - one is measured in 
meters per second and the other is measured in bits per second.

Suppose you and I were signaling each other with flags. At a great distance
we'd have to use large flags that we couldn't wave very fast. The speed of 
light remains constant. (If you're far enough away I can't see
you.)


 JP>   explanation of this DSL rate vs cable. When I get back to my library,

The physical plant for cable TV is superior - often a cable system can deal
with 1400 MHz signals. A twisted pair like the phone company uses might be
only capable of 2-3 MHz. (The twisted pair stuff in LANs is different.)

That said, the broadband companies are in competition. Recent DSL specs
top out at 6-7 MHz ; cable modems have long had a spec limit of 31 MHz.
For now, they compete.

 JP> I will turn up a few pages seeking why. I was never quite pushed into
 JP> this but it baffles me now. Is this also the reason why when more users
 JP> are on-line on cable, the rate goes down,  collisions ???

Yes. More collisions means more retries ; throughput suffers.
Interestingly, in a G-3 cell phone data setup (a CDMA system 
like Verizon or Sprint) more users within reason increase throughput 
because of the increased "randomness" of channel to channel interference!


 JP>         On DSL, would you happen to know what frequency these traps are
 JP>   letting through ? Rather I think, they are blocking it and letting
 JP>   audio through as the traps are on the handsets.

Systems vary ... but DSLs can share both analog and ISDN lines 
(I think) so the traps have to be about 150 KHz.

Regards, Gordon
... MultiMail, the new multi-platform, multi-format offline reader!
--- MultiMail/Win32 v0.46
 * Origin: COMM Port OS/2 juge.com 204.89.247.1 (281) 980-9671 (1:106/2000)