Manual configuration can eliminate the negotiation process required for automatic configuration,
but it adds substantially to the configuration process. It requires router configuration
changes if the modem is changed, possibly through an upgrade or replacement to a different
vendor or model. Manual router configuration requires knowledge of the AT, or Hayes, command
The attention (AT) commands are used to configure the modem and, for most purposes, are
used to create a standard configuration methodology for modems. There are differences from vendor
to vendor in the function of each command, but for the most part they have been standardized.
AT commands enable configuration and diagnostic services to become fairly advanced,
including settings that report the modem’s status, the quality of the network (phone company)
connection, and the configuration of flow control and other modem functions. Software, including
terminal software, will frequently provide these commands upon selection of a menu-driven
function, which insulates the user from needing to learn and use the commands.
NOTE:Please consult with the modem manufacturer regarding the appropriate codes
for your modem.
Most modems have a number of commands in common, and many of these are quite useful
for the administrator. These commands are listed in Table 23.3.
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