[ale] Telco Terminology

Wed Jun 9 23:48:51 EDT 1999

Sender: tew2
Message-ID: <375F3336.4FC5393 at wiencko.com>
Date: Thu, 10 Jun 1999 03:38:30 +0000
 From: Tom Wiencko <tew at wiencko.com>
Organization: Wiencko & Associates, Inc.
MIME-Version: 1.0
To: Alan Bowman <aminus at mindspring.com>
Subject: Re: [ale] Telco Terminology
References: <Pine.LNX.4.05.9906092129410.564-100000 at eris>
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Alan Bowman wrote:
> 
>  So that I (and possibly others) can better follow the recent thread
> regarding xDSL lines, could someone please define the following terms:
> 
> CO

Central Office.  The telephone switch house.

> SLC

Subscriber Loop Carrier.  Registered trademark of Lucent (formerly
AT&T, formerly Western Electric).  The thing that collects up a bunch
of phone lines from houses and businesses and sends their signals and
information via a concentrated form to the switch (at the CO!).

> demarc

Short for "point of demarcation of responsibility."  The physical point
to which the phone company is responsible for delivering service.  Past
that point it is somebody else's problem.  The term "demarc" is 
generally used in commercial installations, and the term "network
interface" used for residential.  They mean essentially the same thing
unless you are a telecom attorney or an installer.

> physical copper line

One or two pieces of copper wire, creating an electrical circuit from
one spot to another.  As opposed to fiber, wireless, microwave, or 
other transmission media options.

> 
>   And could I also get a definition of, and an explination of the
> differences between:
> ADSL
> SDSL
> IDSL

xDSL means (something) Digitial Subscriber Line.  A way of moving bits 
over the copper line to your house. Very cool technology. 

ADSL = Asymmetric Digital Subscriber Line.  
The number of bits per second in one direction does not equal the number
of bits per second in the other direction (you can receive faster than
you can transmit).  Has the significant advantage that you can run
a regular telephone from the same line!  Yes, data and dial tone
from the same pair of copper wires.

SDSL = Symmetric Digital Subscriber Line.  
The number of bits per second in one direction equals the number
of bits per second in the other direction (you send and receive 
at the same rate).  Sadly, no dial tone.

IDSL = ISDN Digital Subscriber Line.
Complete black magic.  Basic Rate ISDN (two 56K digital "bearer" 
channels and one 16K "Data" channel (not really used for data, but
rather for signalling - which is data in the telco world)).  Looks
just like ISDN to the end user, but is a lot cheaper to provision
and support for the telco.  

If you want to know more than any normal human should ever know
about xDSL technology, Ascend Technology has a wonderful set of
white papers on this stuff.  Check out:
http://www.ascend.com/3593.html

> 
>   Maybe I'm the only one on the list who doesn't use these words in
> daily conversation, maybe I'm not.  But I'd still like to know what they
> mean.
> 

Not to worry.  Most people in the telco industry don't know them all
either.  Most people out of the telco industry think they know them
but get them wrong.

Act like you know what you're talking about, and nobody will ever
challenge you.

>   Thanks,
> 
> ...alan
> 
> --

Anytime.  

-Tom

-- 
------------------------------------------------------------------------
Tom Wiencko                                              tew at wiencko.com
President - Wiencko & Associates, Inc.                    (404) 255-2330
Telecom Consulting & Project Development -- Wireline, Wireless, Internet