Checking Your Line Quality

If you think your noisy phone line is causing problems with your modem, check the following:

Check the Line for Noise

First you need to get rid of the dialtone so you 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 a busy signal. The easiest and most common across all areas is a "1". Is your dialtone gone? Now listen and really concentrate while you are doing so because you are only going to get 30 seconds before it times out and gets replaced by a busy signal again.

This is the first major step to checking if you have a good line for a modem or not. Is it quiet? No pops, bangs, crackles, creaking, or faint voices in the background from other people's conversations. All or any of these noises will cause you a problem on a high speed modem link.

Just what are these noises? Well, it 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. 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.

Check the Phone

Let's presume you have one of these noises to some greater or lesser degree. Next you need to check the phone itself. After all, if it's just the phone causing the noise, it won't affect the quality you get from the modem now. If you have a spare phone, take it and plug it into the same socket and then check for noise again. If you don't have a spare phone, it might be worth heading to the local electronics store to pick up an inexpensive phone.

Check the Modem

Let's assume now that you are happy with the perceived "quietness" of the line. Now you move to the modem. How can you check if you 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 you are going to do is to get the modem to go on line, but not actually dial out a full number (similar to what you 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 you'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. If you normally use 1st Reader or Robocomm, 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.

Now type this:


(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) while 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.

THIS time, it's going to be your modem that may "time out" before your phone line does. 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. No noise? If your modem hasn't already timed out, drop the line by typing "ATH". If you did hear 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.

Modems With a Rockwell Chipset

OK, 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, and whether it has a Rockwell chipset in it or not. How do you find out? The easiest way (and most standard) is to type 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."

If you have a Rockwell chipset, follow this procedure:

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, 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 example above, that would be -20dbm (reasonable) and 8 (also reasonable). Higher figures mean worse connections. Anything higher than about -24 with the first, and you'll be seeing bad connects or possibly none at all. Higher than 15 on the second, and you've got real line problems on your circuit that your Telco should be able to sort out.

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.

Other Modems

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. 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. Unfortunately, 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 you are going to have to consult your manual.

If you've got noise and a low line level, you need to contact your Telco provider. Explain to them that you are using a modem on your line, you are getting poor cct quality figures from your modem, and that the line level is low. You are entitled to have this problem corrected. Make sure that you say there is nothing wrong with your normal voice communications (if that is the case...) otherwise 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 the noises 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.

© 1997 Ascend Communications, Inc.