Modem Help

Correcting Modem Hang-Ups

When our modems detect a change in phone line quality, they will automatically send a command to your modem to "retrain" to a higher or lower speed. If your modem does not retrain, the connection will be lost and your modem will hang-up.

Dropped Carriers, & Abnormal modem hang-ups

One of our biggest battle is dropped carriers. There are many different variables that we need to take into consideration while addressing this issue. Here are a few things that are Extremely Important

1. Do you have call waiting?
   
   
2. Check by dialing from the telephone line your modem uses and dial a *70 from a dial tone. If you get anything other than a dial tone after you push these numbers, you do not have call waiting. Contact your phone company for more information on the services you receive. Now verify that you deactivate call waiting by looking at the phone number you dial in the software configuration.
   
   
3. Look for patterns. Usually if you get cut off at a certain time of the day, perhaps someone is doing construction in your area, or something of that nature. If it happens on a regular basis, there usually is something wrong locally.
   
   
4. Windows Users verify the UART chip.
   
   
5. The UART, or the Universal Asynchronous Receiver/Transmitter controls the Input/Output of the serial port. The CPU communicates with the serial device by writing in the UARTs registers. Not every computer is equipped with the newer 16550 UART, so it is important you know which UART you are using. The older 8250 UART is physically incapable of handling modem speeds greater than 9600 bits per second (BPS) because of possible input data overruns that can occur if a character is left in the input register when the next byte is received. The newer 16550 UART allows reliable data transfer at high speeds with its 16-byte first in, first out (FIFO) input register. The FIFO feature in the 16550 can buffer up to 16 bytes at a time whereas the older 8250 only has a 1 byte FIFO. Check for the UART you are using by entering into MSD (Microsoft Diagnostics) from a DOS prompt. Select [C] for Com Ports. Look at the UART used for the communications port you use. If you have a 16550 UART ensure the following settings are in your SYSTEM.INI file under the [386 Enh] section. (For windows 3.1 only)

   MinTimeslice=20
   WinTimeslice=100,50
   COMnFIFO=1
   COMnBuffer=1024

   n is equal to the communications port you are using.
   

6. While you are there editing your SYSTEM.INI it is a good idea to see if you are using the proper Communications Driver. Look for comm.drv=comm.drv under the [Boot] Section. If it is anything different, change it.
   
   
7. Macintosh Users verify a Hardware Handshaking Cable
   
   
8. Are there any additional devices attached to the internal telephone circuit that might exceed the LN (Load Number) limit? This might exhibit itself as weak (lower speed) and/or dropped connections.
   
   
9. Each modem's documentation states the LN number for that modem. Remove all additional devices (other telephones, fax machines, etc.) from the circuit and see if things change.
   
   
10. Are there any local sources of noise and/or interference? Noise related problems can cause excessive retrains or failure to negotiate a connection. Look for local sources of noise or interference. This may include faulty local connections or connections near strong sources of EMI. Try a different phone outlet if available. Move devices that might cause interference to a different location. Try insulating the phone line with devices available at most electronic stores.
    
    
11. Are there any non-local sources of noise and/or interference? This would cause the same effects as above; excessive retrains or failure to negotiate a connection.
    
    
12. Try relocating your modem to a different phone line or different location if possible. This may mean trying a test from the office instead of home or vice-versa. It may help shed more light on the problem if the connection can be tried from a location with a different three digit phone number prefix than the original location. (555-1212 instead of 554-1212). If the call is long distance, you can try using a different long distance company (AT&T vs MCI or Sprint) for instances using prefix numbers. As another test, try lower protocols and speeds if possible (V.32bis instead of V.34).
    
    
13. When was the last time you replaced your I/O card? Taken from a Newsgroup:
    
    

14. Subject: random disconnects
    
    I would like you to know that for several weeks 
    I experienced many random disconnects as described 
    by many others.  I finally figured out that the 
    problem was on my end.  I previously had been using 
    an internal modem and had few if any problems.  I 
    bought a 28.8 external (Boca) and started having 
    problems, though I did not realize the change had 
    anything to do with the problem.  It did, I had a 
    very old I/O card.  Replacing the I/O card with a high 
    speed card definitely did the trick.  I don't believe
    I have had a single random disconnect since.  I have 
    a 486/40 which is almost 4 years old, I just did not 
    think about the outdated I/O card until I had a conversation 
    with a friend and we discussed my problem.
     

15. Ensure you have the latest firmware for your modem. You can usually find this on the home page of your modem.
    
    
16. It is also a good idea to get the phone company involved. Ask them to check the quality of your line because you have a fax machine. Phone companies hate modems and they will probably give you a standard lecture informing you that they don't guarantee more than 3 bits per hour. Curiously though, you may find more sympathy and responsiveness if you tell them that you have a Fax problem.