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From: syd@dsi.com (Syd Weinstein)
Newsgroups: comp.dcom.telecom
Subject: Re: Device Given to me With "Data Lines"
Message-ID: <16372@accuvax.nwu.edu>
Date: 24 Jan 91 05:15:51 GMT
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Organization: Datacomp Systems, Inc.  Huntingdon Valley, PA
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X-Telecom-Digest: Volume 11, Issue 63, Message 3 of 6


tel@cdsdb1.att.com writes:

>Any time we order a "Data Line" for our computers here, we are given a
>device to put inline between the modem and the phone jack.  It is a
>box about 4 X 2 X 1 inches, has one two-pair modular cord to plug into
>the phone jack, and one modular outlet that the modem plugs into.  It
>also has a switch labeled FLL and PROG.

>My question is: What is this box, what does it do, and what do FLL and
>PROG stand for?  Anytime I ask the techs what they are for, they have
>no idea.  They are just told to give them to the customer.

The box is a two wire to eight wire adapter.  Now don't panic, it
doesn't touch the two wires themselves, but adds some other signals.

It leaves tip, ring, A and A-1 alone (the center four).  It does add a
programming resistor -- more in a second -- and a pad optionally to
the loop.

In a true data circuit, you want the outgoing carrier to arrive at the
CO at -10dbm.  However, the loss in your loop varies by condition,
length, and other factors.  What the traditional modems did was output
their signal at a higher level, and have the phone company measure the
loss in the line and add a pad.

The RJ-42,3,4,5 series eight wire jacks offer this ability by coming
in flavors (values of the pad) to match possible line losses.  These
flavors have a resistor that an appropriate modem can use to adjust
its output to the correct value to get the best signal at the CO.

This is the PROG position.  No pad is placed on the line itself, and
the modem does the work via a resistor on two of the unused positions.

In the FLL, or Fixed Loss Loop, position, a pad is placed to drop the
output volume by a fixed amount, and the line is not measured.

I have Bell of PA put these on all our modem lines, and they call them
RJ45's.  Note there are other ways of wiring the boxes, and then they
have different numbers, but all the same purpose.  Other numbers
indicate if they support exclusion key wiring, automatic jumpering,
etc.

Are they worth it?  Most interactive modems don't use them, if your
modem has a four wire (six positions, four used) mod plug, it doesn't
use them.  If the modem has an eight wire modular plug, it probably
does.

However, some modems are loud on purpose, to compensate for long loops
and the loss.  These sometimes need a pad, and the FLL position
provides that.

However, what I like better, is if you have Bell of PA put this jack
in, the line is assigned a 3NDDA number (3NDDA XXX-XXXX where x's are
the phone number) Then you get Data Repair service to call instead of
the usual repair service, (Yea, no more is the line ok questions, just
a knowledgable person on a test board actually answering the phone)
and here in Phila, a two hour response time guarantee. (And I mean
that 24 hours a day. I have gotten things fixed at 3 AM).  And all of
that for no more per month that without the jack, only a one time
charge up front.  And that charge, here, used to be reasonable.  I
haven't done it in a while, but it was about twice the charge without
the special jack.  


Sydney S. Weinstein, CDP, CCP Elm Coordinator Datacomp Systems, Inc.
Voice: (215) 947-9900 syd@DSI.COM or dsinc!syd FAX: (215) 938-0235