Modem-Specific Troubleshooting

If you are confident that a modem is installed and configured correctly, but it's still not working properly, you can test and configure it by using special commands from the AT command set. Table 12 lists some of the most commonly used AT commands.

Table 12 Commonly Used AT Commands

AT Command



Sets the modem to auto-answer


Hangs up an active connection


Dials a number


Resets the modem


Displays the name and model of the modem

In general, getting the modem to respond to an ATZ command is a good enough indicator that the modem is functioning.

Troubleshooting Authentication Failure

All forms of remote connectivity should require some form of authentication to confirm that those trying to access the remote resources have permission to do so. As a network administrator, you can expect to become very familiar with authentication troubleshooting. Quite often, authentication errors result from users incorrectly entering usernames and/or passwords.

Authentication issues can also arise as a result of permissions changes in users' accounts. If you're troubleshooting remote connectivity and you have confirmed that the correct username and password are used, you should confirm that the user has the appropriate permissions to access the network.

The third and perhaps least likely cause for authentication failure is a downed authentication server. In such a circumstance, you are likely to receive numerous calls regarding authentication difficultynot just one or two.