Rd: [ale] PBX

[John M. Mills]

Diving into the unattributed thick of it:
On Thu, 12 Dec 1996, *.* wrote:

> Date: Thu, 12 Dec 1996 15:54:34 GMT
> From: "*.*" <pvk at primenet.com>
> To: ale at cc.gatech.edu
> Subject: Re: [ale] PBX
> 
> 
> >The PBX (phone line) is the culprit. What make the situation worse is that the
> >phone company can do whatever they want to the line so long as it is voice
> >quality. The only guaranteed line is the "data line" from the phone company
> >(read that as $$$$). I've heard of phone companies out west (of the
> >mississippi) who place companders (COMpress/exPANDER) in their lines. And
> >these magical electronic boxes play havoc with modems. Voice sounds great, but
> >unusable with modems.

I thought that companding and echo suppression were variables which could be
turned off by the sending station through appropriate signaling, and I always
assumed it would be a pretty lame modem which did not turn these "features"
off when establishing its connection.

I have relatively little experience with telephone network signalling, so I
may well be mistaken on this.  It could also be that signalling controls
fail across some inter-carrier links,  but do remember that you are only
buying about 3.5 _K_Hz of bandwidth here, and getting 20-30 KBaud across it
must be a real hat trick.

DISCLAIMER:  I'm just a simple M.E.  Perhaps someone more knowledgeable
with regards to modem design would care to contribute.

Regards --jmm--

John M. Mills, Senior Research Engineer   --   john.m.mills at gtri.gatech.edu
   Georgia Tech Research Institute, Georgia Tech, Atlanta, GA 30332-0834
        Phone contacts: 404.894.0151 (voice), 404.894.6285 (FAX)
           "Lies, Damned Lies, Statistics, and Simulations"