2.3 Modem Configuration
2.3.7 Modem autodiscovery 

If no modem is specified for a particular line and you have provided the modem autoconfigure discovery command, the access server attempts to autodiscover the type of modem to which it is attached. The access server determines the type of modem by sending AT commands to the modem and evaluating the response. The Cisco IOS software initially tries the first of the modemcap strings to see if the modem initializes properly. If not, the Cisco IOS software cycles to the next string and repeats the process until the appropriate string is found. Usually, if none of the strings properly initialize the modem, you must manually configure the modem.

Sometimes, the router fails to recognize a modem, even though it might be part of the modemcap list. If you have verified that your modem can be configured by using an initialization string from one of the existing scripts, you can issue the modem autoconfigure type command, as explained in the next section.

The following is an example of the modem autoconfigure discovery command:

Router(config)#line 1 16

Router(config-line)#modem autoconfigure discovery

This command instructs the access server to do the following on lines 1 though 16:

  • Send the AT string at various baud rates until it receives an OK.

  • Send a variety of AT commands that attempt to receive a complete identification of the modem from the access server modem capabilities database.

The specific modemcap entries found on a particular system are determined by the hardware and Cisco IOS software version that are installed. Whenever possible, specify a modem type to eliminate the router overhead when modem autodiscovery is used. If you list a specific modem type, initialization proceeds more quickly.

If the access server cannot determine the modem type, the default modem entry is used. Any modems that are not currently supported in the list can be manually added to the list to be autodiscovered in future communication, as you will see later in the section "Fine-Tuning Modem Autoconfiguration."