Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!sun-barr!rutgers!cmcl2!phri!roy
From: roy@phri.UUCP (Roy Smith)
Newsgroups: comp.dcom.modems
Subject: Why are dial-up modems improving faster than direct-wire ones?
Message-ID: <3971@phri.UUCP>
Date: 1 Sep 89 01:20:26 GMT
Organization: Public Health Research Institute, NYC, NY
Lines: 23


	Right now I'm talking to you via a Trailblazer which can do
19.2kbps over plain old dialup lines with something like 3 kHz bandwidth
(and, in fact, can manage a respectable fraction of that over horrible
dialup lines).  On the other hand, I've got a 4-wire leased line (LADC)
circuit at work which I can barely get 128 kbps out of.  It's about a mile
of 26 gauge wire with a measured loop resistance of something like 700 ohms
and useable bandwidth from DC to over 100 kHz.  30 times the analog
bandwidth of a dialup connection, yet I can only coax about 6 times the bit
rate through it.  Not to mention the additional factor of two improvement I
should be able to get because I've got 4 wires.  I've seen a modem which
claims to be able to do 230 kbps over our line, but it doesn't work.  On
the other hand, I've heard of V.32 modems which can do 38.4 kbps over
dialup lines.

	So, my question is why do modern dialup modems get so much better
performance (compared to the channel they have to work with) than leased
line modems?
-- 
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
{att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu
"The connector is the network"