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From: johnl@iecc.cambridge.ma.us (John R. Levine)
Newsgroups: comp.dcom.telecom
Subject: Re: Device Given to me With "Data Lines"
Message-ID: <16374@accuvax.nwu.edu>
Date: 24 Jan 91 17:54:50 GMT
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In article <16347@accuvax.nwu.edu> you write:

>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.

>I am told that NJ Bell charges an arm and a leg for these boxes.  Is
>that just a ploy to make money or are they useful?

They are useful in some circumstances.  The signal loss from the CO to
the customer premises varies a lot depending on the distance,
condition of the wire and such.  Some data communication equipment,
particularly older stuff, depends on knowing the amount of the signal
loss.

There are two ways to handle this: Fixed Loss Loop (FLL) puts a PAD
circuit in the connector block to make the total loss between 8 and 9
DB.  The installer measures the loss from the CO (by calling a test
number that produces a known signal) which is usually less than 8 dB
and puts in a block with an appropriate PAD to bring the total loss up
to spec.  Programmable (P or PROG) puts a resistor into the connector
block whose value depends on the measured loss.  The resistor is not
directly connected to the phone line but is connected to pins PR and
PC (7 and 8) of the jack for the use of a PAD in the equipment plugged
into it.  The FLL/PROG switch unhooks the connector block PAD in PROG
mode, since equipment that uses the programming resistor doesn't want
its signal pre-attenuated.

When the jack has both FLL and PROG with a switch, it's called an
RJ41S.  With the programming resistor only, it's a RJ45S.  With
various obsolescent arrangements that involve a telephone with a DATA
button, its an RJ42S, RJ43S, RJ46S, or RJ47S.  These are all the same
physical data jack, but wired in different ways.

If you are using something like a V.32 or Telebit modem, the data line
is overkill since these modems have their own compensating circuits.
Also, be sure that the installers are measuring the loss and setting
the PAD and programming resistor appropriately.  If they aren't, the
jack is no better than a regular voice RJ-11 and, in all likelihood,
the signal quality on the line isn't any better than a POTS line,
either.


Regards,

John Levine, johnl@iecc.cambridge.ma.us, {spdcc|ima|world}!iecc!johnl