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You can manually configure the modem instead of having the router force a
configuration on it. On the modem side, you can use the standard
configuration commands to do the following:
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Perform hardware
flow control
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Lock DTE speed to
ensure that the modem will always communicate with the access
server at the specified speed; as an example, when you use an
async interface, you lock the speed to its theoretical maximum
of 115.2 Kbps; the router speed command sets both transmit and
receive speeds
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Hang up when you
quit a session
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Have the CD signal
truthfully reflect the carrier state
To manually configure your modem, you
most likely do a reverse Telnet to your modem and apply some AT
commands. In general, each modem vendor has its own modem command
set that differs from other vendors' command sets. However, the
following modem commands are common among most vendors:
Warning: Because the Caller ID
function activates on the second ring, hackers typically target
modems that answer on the first ring. If a modem takes more than one
ring to answer, many hackers don't pursue the matter. You are,
therefore, advised to set your modem to at least ATS0 = 2, thus
pretending that your line subscribes to Caller ID.
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Lab
Activity |
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You
are working for the Atlanta Bread Company and
would like to setup out-of-band management on
your router. You will properly configure an
asynchronous connection on your router and
dialin from a remote location. |
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AT Command Sets
AT commands stands for attention commands that are used to address
the modem and force a certain behavior from it. The following is a
listing of different command sets that exist and examples of
commands used in the modem modules of Cisco 2600 and 3600 series:
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Alphabetic
command set -- Q0 enables output of result codes.
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Caret command
set -- ^V Displays the modem current Flash memory bootstrap
revision.
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Dollar
command set -- $Bn sets the serial port rate to n bps, for example
$B 115200.
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Percent
command set -- %Bn sets the modem port data rate, for example %B
33600.
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Ampersand
command set -- &D3 sets the modem on-hook and resets when
detecting an on-to-off transition of DTR.
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Parenthesis
command set -- )M1 autoadjusts the power level for cellular
modems.
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Asterisk
command set -- * I displays the modem identifier.
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Hyphen
command set -- -DL redials the last number dialed.
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Colon command
set -- :Dn sets manual dial.
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@ Character
command set -- @E gives detailed modem call status.
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Backslash
command set -- \F displays stored phone numbers.
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# Character
command set -- #E0 enables the escape code sequence in answer
mode.
AT commands can be found at the
following web link.
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