Modem Frequently Asked Questions

Q:

A:

                                           
  Cmd      
___________________________________________________________________
 ATI       
 ATI4        
 ATI9  
        

Q:
 Why won't my 28,800 bps modem connect at that speed?


A:
 
 Bandwidths of 3200 Hz and an SNR of 30 dB or more are required to
achieve a connection at the 28,800 bps rates.  This is higher than
the quality required by local phone lines although many local lines
do meet this standard.

If you consistently connect at 26400 or above, consider yourself fortunate. 
Even if you consistently connect at lower speeds (e.g., 24000 or even 21600),
there may be little you can do, but see the next question for some things to
try.

See Also 28800 Connect FAQ at Aimnet.


Q:
 I frequently have problems getting connected and having my connection dropped.


A:
  This can be caused by a lot of things.
I. Verify your setup:
 1.  Check all your settings (flow control, modem scripts, ..)
 2.  Check that you have the right modem cable.  On Mac's you 
     need a high speed modem cable with most modems 9600bps and above.
II. Trial and error:
 1.  See if you can borrow another modem and/or serial cable and try it.
    A bad modem can cause this.  We've seen both Global Village and
    Apple Express modems that resulted in dropped connections.  Replacing
    the modem fixed the problem.
 2.  Try a different communications package. e.g. a Terminal emulator
     dialing into a terminal server.
 3.  Try dialing a number at a different site.  We've seen situations
    where NJ Bell had carrier/equipment problems with inter office
    trunk routes.
 4. Try connecting to known good 28800 numbers (e.g., Hayes at 800-"US-HAYES;
    Multi-Tech at 800/392-2432; USR at 847/982-5092). 
    This will at least tell you whether the problem is at your end or the
    other end of the connection. (The USR number is particularly useful,
    because you can get an on-line reading of connection quality from a
    USR BBS command.) 
III. Check your wiring and connection to the CO:
 1. If you have call waiting, the tone indicating an incomming call
     can cause the line to drop.  You can subscribe to "tone block"
     which allows you the enter "*70W" before the number to stop the tone.
 2. A T200 TouchPhone plugged in line with your modem can cause this.
   The phone is a flat white phone with touch pad numbers on the front.
   The problem is caused by the fact that the phone recharges it's 
   batteries (for the number memory) by charging off the line.. Unfortunately
   this usually makes the modem hang up.
 3.  Loose connections on in your house wiring, either the outlet where
   your modem is connected or your network interface unit from NJ Bell,
   can cause it.
 4.  Try another phone cord.
 5.  Try disconnecting the rest of your house phone wiring at the Network
    Interface (usually in your basement) and run a line directly to your
    modem.
 6.  Try another line if you have one.
 7.  Check See if you can get NJ Bell to check your phone line.
IV. Try increasing the transmit level
    MultiTech sugested:
  The only modification you can make to your modem to overcome line conditions
  is to use the S20 register.  At the end of your init string put S20=3D11 (this
  is default).  This number would actually refer to a -11db transmit rate.
   I've usually found improved connections by setting S20=3D14 (-14db).  The
  range for this value is 8-20.  This will take some experimenting on your
  part.

----
See Tips for Connecting from overseas or other places with Noisy lines.
----
From: "sek" 
Subject: Re: ARA

When I was experiencing similar problems 
(dropped connections, slow connections, time-outs) it turned out to be the bad 
circuit/wire into our house.  I was having these problem and was trying all 
sorts of things, different modems, different software configurations, new 
cables, etc. but the problems persisted.  One day we lost phone service to our 
house completely and NJ Bell determined the problem was somewhere between our 
house and the central office.  When service was restored (I never heard exactly 
what needed to be replaced) the problems went away.  Since that time I can 
count on one hand the number of dropped connections I've had.  Before that it 
was a daily occurrence.

----------------
From: mcbride (mcbride,donald t)
Date:  4 Aug 1994   8:45 EDT
Subject: Re: Dial-in problems


  Thanks.  That's good to know; Not that you had bad wiring but that
the problems are not all caused by the software/hardware we are using.
  I had a similar problem and I suspect a lot of people do.  My original
problem was fixed by building a new house on the same property and getting
NJ Bell to run my drop from a new terminal (my old drop was 1/4 mile long and
25 years old).
  I had a problem in the new house which caused errors with the new
28.8 modems.  It turned out to be a loose connection in the Network Interface
unit where my house wiring connects to NJ Bell's drop.
  I've asked the Phone people in Dick Riegers group and our NJ Bell
account people if there is some type of device we can get that people
can borrow to test their lines at home.
  NJ Bell's official response if you report a trouble is that they
don't support high speed >2400bps modems on POTS lines.
  I suspect this kind of thing will be more frequent when we get more
work at home people.
		Don
--------------------
Subject: Re: Corrupt Frames
Date: Wed, 10 Aug 94 09:47:54 -0400
|>
|>   I can't find a definition of "Corrupt Frames" in the GatorLink
|> documentation.  A user recently had a session which showed a
|> large number of corrupt frames in the log and got dropped
|> although the log said "Client initiated disconnect"
|>
|>                   

 Now, bad crc's can occur for a few reasons:  1) bad
physical connection (i.e. cabling, phone line noise, etc.), 2) bad
software (i.e. the code that was transmitting the frame to us somehow
trashed some bits), or 3) any other outside factor that might corrupt
a bit here or there, like the modems just not liking each other  :-)

- bill

  We've also seen CRC errors caused by using the wrong modem script. (Don)


Q:
 Is there any way to test the condition of your lines.

A:
As far as local loop testing, there aren't any valid tests you can do to
determine line conditions.  You can, however, call a BBS with a terminal
program and then type "+++at" to break back into command mode.  If you then
type ATL8 you can see a breakdown of some line condition info.


Q:
 Are there any settings that will help with noisy lines.

A:
From: JBT@multitech.com (Jay Taylor)
Organization: Multi-Tech Systems, Inc.
Date: Mon, 2 Dec 1996 17:23:44 -0600

The only modification you can make to your modem to overcome line conditions
is to use the S20 register.  At the end of your init string put S20=3D11 (this
is default).  This number would actually refer to a -11db transmit rate.
 I've usually found improved connections by setting S20=3D14 (-14db).  The
range for this value is 8-20.  This will take some experimenting on your
part.