Adding modems

Problems dialing out

The most useful tool for diagnosing dial-out problems is the -x9 option to cu(C). This option causes cu to display diagnostic output when attempting to dial out. To get a debugging output, enter the command:

cu -x9 phone_number

where phone_number is the phone number of the system you wish to dial.

You may experience one of the following problems on dialing out:

Modem dials, but does not connect

If your modem dials correctly, but the call never connects:

  1. Verify that the phone number is correct and operational and that the phone line to which the modem is attached is not faulty. To do this, unplug the modem from the telephone line and plug in a regular telephone. Manually dial the number to make sure that the modem on the other end of the line is answering the call.

  2. Listen carefully to your modem while it dials the call. Some business phone systems require a pause between certain numbers. Use a dash in the cu command to indicate a pause of two seconds. For example, if you enter: 9----4581234, the modem pauses for 8 seconds after dialing the first number.

    The dialer translates the dash passed to the cu command into the appropriate code for your modem. For example, the dialer translates the dash into a comma before sending to an AT-compatible modem.


When you try to dial out on the modem, the following message is displayed:

   Connect failed: NO DEVICES AVAILABLE
To solve the problem:

  1. Verify that the modem port has an entry in the /usr/lib/uucp/Devices file. Here are example entries for an AT-compatible modem running at 9600bps on /dev/tty1A:
    ACU  tty1A  -  9600  /usr/lib/uucp/dialHA96V
    Direct  tty1A  -  9600  direct
    These lines must not being with pound signs (#) or whitespace.

  2. Verify that the modem port in Devices has the correct line speed associated with it. If you specify the line speed with the -s option to cu, verify that there is an entry in Devices that corresponds to that line speed.

Modem answers, but terminal displays garbage

If the modem answers, but the terminal displays garbage characters:

  1. Verify that the site that you are calling is set to the same data bit and parity values that you are using. By default, cu uses 8 data bits, and no parity. To change the values to 7 data bits and even parity, enter cu -e. For 7 data bits and odd parity, use cu -o, and use cu -oe for 7 data bits and no parity.

  2. Verify that the remote computer is set to the same line speed that you are using.

    If you are dialing into another UNIX system, you can force the remote site to switch to the next line speed by sending a break signal. To send the break signal during the login sequence, enter:


  3. Check for noise on your phone line. Noise problems become more acute when operating at higher speeds. Normally, when there is a problem with line noise, garbage characters appear on the screen in short bursts or continuously, as if a system on the other end of the line is trying to send valid data.


UUCP and cu create a lock file named LCK..line in the /usr/spool/uucp directory. This file is used to prevent anyone else using the modem connected to the serial device line if it is already in use. If the lock file is not removed after a connection has been closed, the modem may not be setting Carrier Detect (CD) correctly.

root must remove the lock file before anyone can use the modem again.

Modem does not hang up

If your modem does not hang up at the end of a call:

  1. Verify that you are using a serial port with modem control that is configured in the /usr/lib/uucp/Devices file and that the ``ACU'' entry for the modem port comes before the ``Direct'' entry for the direct line. If you are using a non-modem control port, change the port to the corresponding modem control port. For example, the modem control port associated with tty1a is tty1A.

    NOTE: Non-modem control ports should only be used with terminals, and when configuring the modem.

  2. If the CD (Carrier Detect) light on the modem does not go off when the call is disconnected, check the modem switches to verify that the modem is set to detect the incoming carrier. If your modem is AT-compatible, use the AT&C1 command. This forces the carrier detect line to follow the presence of a carrier on the phone line.

  3. Check the modem switches to verify that the modem is set to detect DTR (Data Terminal Ready). The modem should hang up when DTR goes from high to low. If the modem is AT-compatible, use the AT&D2 command.

  4. Some modems have a switch that can be set to ignore DTR; make sure that this switch is off.

Double echo

If you get a double echo when you dial out on your modem, check the setting for local echo. If local echo is enabled, disable it.

Next topic: Problems dialing in
Previous topic: Troubleshooting modems

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003