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82 Chapter 4: Configuring Asynchronous Connections with Modems
Example 4-6 provides the basic configuration for an asynchronous line. Once the DTE device
has been configured, you must set the DCE device to communicate with the modem by using
the AT commands.
Configuration of the Attached Modem
In the early modem days, the Hayes command set was the de facto standard; however, there
was never a ratified industry command set. Today, rather than converging to a general standard,
the modem industry has actually diverged. Nonetheless, the AT commands documented in
Table 4-4 are considered "standard" and should work on most modems.
A CCNP or CCDP should be familiar with these commands. For many modems on the market
today, commands not in this table are used to configure the modem fall into the category of not
standard.
The correct initialization string must be sent to the modem for proper operation. You can do this
by using a chat script or the modem autoconfigure command. The former method is the most
common.
Modem Autoconfiguration and the Modem Capabilities Database
Modem autoconfiguration is a Cisco IOS software feature that enables the router to issue the
modem configuration commands, which frees the administrator from creating and maintaining
scripts for each modem. The general syntax for modem autoconfiguration is as follows:
modem autoconfigure [discovery
| type modemcap-entry-name]
The two command options for the modem autoconfigure command are as follows:
·
type--This option configures modems without using modem commands, or so it is
implied. The type argument declares the modem type that is defined in the modem
capabilities database so that that the administrator does not have to create the modem
commands.
Table 4-4
Standard AT Commands
COMMAND
Result
AT&F
Loads factory default settings
ATS0=n
Auto answers
AT&C1
CD reflects the line state
AT&D2
Hangs up on low DTR
ATE0
Turns off local echo
ATM0
Turns off the speaker