The following is borrowed from the Ascend homepage for your use.
Checking Your Line Quality
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So you think your noisy phone line is causing you modem problems
but how do you check? What do you look for?
Well the first thing is quite obvious if you stop and think about
it. When you pick your phone up and listen, what do you hear?
Dialtone I hear you say! No, what I meant was, what do you hear
in the background. OK, first we need to get rid of that annoying
dialtone so we can really listen to the line. Dial a number, any
number but obviously one which is valid for your area so that you
don't get the dialtone replaced by that equally annoying (for our
purposes!) busy tone. The easiest and most common across all
areas is a "1". So dial this digit. OK, dialtone gone
yes? Now listen and really concentrate while you are doing so
cause you are only going to get 30 seconds before it times out
and gets replaced by busy tone again....
This is the first major step to checking if you have a good line
for a modem or not. Is it quiet? No, I mean really quiet, like
almost silent. No pops, bangs, crackles, creaking (yes, really!
I've heard it myself!) or faint voices in the background from
other peoples conversations. All or any of these noises will
cause you a problem on a high speed modem link. Heck, they would
have caused you a problem on an old 2400 link as well some years
back but in this case even more so. Before in the days of slower
baud rates and speeds, they might have caused your transfers to
slow down. Now they just plain won't let you connect!
Just what are these noises? Well they can be caused by many
things but generally it in can be something as simple as a loose
screw on a connector block somewhere between you and the exchange
or water getting into one of Telco’s cable ducts and the
waterproofing (around the cable joints) has started to break
down. In these days of it being much easier to "build your
own extensions" at home, you could have a bad connection in
the house somewhere and not necessarily on the line extension
that's feeding your modem. Other people's conversations (called
"crosstalk" in the trade) are not so easy to pin down
and are usually more likely to be further "into the
system" before the source becomes apparent.
So, let's presume you have one of these noises to some greater or
lesser degree. Next we need to eliminate the phone instrument
itself. After all, if it's just the instrument causing the noise,
it won't affect the quality we get from the modem now, will it?
Got a spare phone? You have? OK, just take it and plug it into
the same socket and then repeat paragraphs 2 & 3 again. You
don't have a spare phone? It might be worth heading to the local
Radio Shack or other electronics store and picking up a cheap
phone. Make sure you test the phone in the shop before bringing
it home.
Let's assume now that you are happy with the perceived
"quietness" of the line and that nothing seems untoward
with it that you can tell with your own ear. Now we move to the
modem but we are still concentrating on physical things really.
How can we check if we have a dodgy plug or socket associated
with the modem? Well, surprisingly, it's reasonably simple but
you'll need to be fairly quick in carrying out the next
"test". What we are going to do is to get the modem to
go on line but not actually dial out a full number (similar to
what we did just now but using the modem instead). To do this
you'll also need to have a phone plugged in too that's fairly
near to where your PC/Modem are. Don't pick up the phone yet.
You're about to enter a command string to the modem so obviously
we'll need to have the PC powered up and talking to the modem
with whatever piece of communication software you use. In the
case of Procomm, Smartcom, SmartTerm, Zterm, etc., it's simply a
case of just firing up the software and getting to a terminal
screen with the "OK" prompt from the modem staring at
you. If you normally use 1st Reader or Robocomm (say) then you'll
need to fire up the Terminal Session for those packages and again
just get to an OK prompt. Don't dial out a number at all.
OK now type this "ATX0D1;" (without the quotes) and
what you should hear (if you have the modem's speaker on) is that
the modem will pick up the line (dialtone heard), then dial a 1
and finally drop back to command mode (OK prompt on your screen)
whilst holding the line open. The next bit is easy or more
difficult depending on the accessibility of your modems’
leads. i.e. internal or external modem. Now pick up the phone and
listen. At this point I should mention that THIS time, it's going
to be your modem that may "time out" before your phone
line does so be a bit sprightly! Check the modem's lead, plugs
and sockets by physically getting hold of them and just gently
pushing and pulling on the lead at both ends. You'll find on
these type of plugs that there is possibly a couple of
millimeters of "play" even when the plug is fully
seated in it's socket. This is enough for our purposes. Again, be
gentle. If there is a dodgy connection, it won't take a lot of
movement before it becomes apparent in the phone you are
listening to. OK, that was good? No noise? Right, if your modem
hasn't already timed out, drop the line by typing
"ATH". If you did here some crackling from that, then
you'll need to get that lead replaced. It could be just the
contacts of the plugs that have become a little tarnished. A good
ink eraser with a fairly sharp edge should clean these up nicely.
OK, now we're down to the nitty gritty. You've carried out all
the above and you are still getting poor high speed connects with
your modem? Now it's going to matter exactly what type of modem
you have. Whether it has a Rockwell chipset in it or not. How do
you find out? Well possibly the easiest way (and most standard)
is either AT&V or ATI4. If you have a Rockwell chipset, from
the former you'll see a complete configuration dump starting with
"Active Profile" then "Stored Profile 0"
followed by "Stored Profile 1" and finally
"Telephone Number Stores". The latter should return a
couple of rows of checksum digits (up to 4 rows) which are the
capabilities of the modem in "hex” speak!
We'll consider that you have a Rockwell chipset in this first
instance. Now follow this procedure as you have two very useful
commands at your disposal...
1. Dial into another modem [a BBS or other service provider] from
a terminal screen (not automatic with a script - manually)
2. Do whatever you need to get your Login prompt [if your service
does immediate PPP or immediate TELNET, use a different service].
3. Pause (do nothing) for at least 1 second.
4. Type "+++" (without the quote marks - just the
pluses)
5. The modem should now have dropped back into command mode and
you
should be looking at an "OK" prompt *but* you will
still be online...
(You'll need to be fairly sprightly at this point as you may lose
the
connection if you aren't quick enough...)
6. NOW you can type AT%L%Q[return]. The modem should return 2
figures on successive lines like 20 8 or something.
These are the Line Level (%L) in -dbm and the Eye Quality Monitor
(%Q) index. In the above example that would be -20dbm
(reasonable) and 8 (also reasonable). Higher figures mean worse
connections. Anything worse than about -24 with the first and
you'll be seeing bad connects or possibly none at all. Worse than
15 on the second and you've got real line problems on your
circuit that your Telco should be able to sort out...
Oh, and when you've finished, you might like to go back online
with ATO (not zero) and then log off normally. You *may* find you
get logged off anyway after you've got the response to %L%Q...
If you do get bad figures from these tests, you'll need to
contact your Telco to try and get your line improved. We'll go
over "What to ask for" in a minute...
So, what do those who don't have Rockwell chipsets do? Well there
are a number of options. If you have a USR based modem (and there
are some "badge engineered" models about) then chances
are you will be able to use ATI6 for your checking. This can be
done either online (see above for how to stay online but get back
to command mode...) or offline as the USR chipset
"remembers" the figures it got from the last connect
you made. I won't go into the full detail of what all the figures
mean (ATI6 produ ces nearly a whole screen full on a USR!) but
the bits you are interested in are BLERS. These are "Bit
Link Error RateS". Ideally, this figure should be 0. If it 1
or 2 after you have been online for a while, then you probably
have nothing to worry about. If it climbs much higher over say a
3-4 minute connect then you are probably suffering from noise or
low level or both; as in the Rockwell situation above. If you
want to know what the rest of the figures mean, consult your
modem manual. Unfortunatel y, the USRs do not give an indication
of the actual received carrier level in decibels/milliwatt (dbm).
If you have neither of these types of modem, then I'm afraid you
are going to have to consult your manual. At least now you should
have a fair idea of what you are looking for though...
So, we've got noise and a low line level. What do we do? Your
Telco provider is the next port of call. Explain to them that you
are using a modem on your line and that you are getting poor cct
quality figures from your modem and that the line level is low.
Try and be polite and they will usually be helpful. You are
entitled to have this problem sorted. Make sure that you say
there is nothing wrong with your normal voice communications (if
that is the case...) else they will just do a normal line check.
If you are on a digital exchange, ask them if you can have the
AGC (automatic gain control) turned OFF and your line setting at
the exchange, set to position "5". In most cases this
should give you a good cct and level and cure your connect
problems at a stroke.
If you are experiencing these funny little noises I described
earlier, be warned that it may take several visits and tests by
the telephone company before the cause of the problem gets rooted
out.
Happy modeming and I hope this has been of help to you...
The above is borrowed from the Ascend homepage for your use.