disconnect the modem, clear the line, make the telnet connection, and then attach the modem. This prevents
a misconfigured modem from denying line access.
Always issue the initialization commands to the modem starting with AT and issue them at the speed at
which you wish the modem to talk to the Cisco router. This ensures that the modem will always talk at the
expected speed regardless of the speed of any incoming modem connection (assuming that you set the
modem to lock on the DTE speed, which is required).
Caveats
If your dialup EXEC connection appears to stop responding, enter ^U (clear line) and ^Q (XON),
then press Return a few times.
●
When you are dialed in, if you type quit and the modem does not hang up, then either it is not
watching DTR, modem control was not configured properly on the Cisco router, or the cabling is
incorrect.
●
If you find yourself in someone else's session (that is, at an enable or a configure prompt) when you
dial in, either the modem is not dropping CD on disconnect or you have not configured modem
control on the Cisco router.
●
If you issue a +++ on the dialing modem followed by an ATO command and discover that your
connection does not respond, the answering modem interpreted the +++ when it was echoed to you.
This is a bug in the answering modem and has been observed on many modems. There may be a
switch to defeat that, but it varies from modem to modem.
●
If you have autoselect turned on in the line configuration, a carriage return is required to get into
EXEC.
●
If you elect to do hardware (RTS/CTS) flow control (which is strongly recommended), make sure it
is enabled on both the router/access server's line (DTE) and the modem (DCE). Having one on and
the other one off will cause data loss.
●
If you have an MDCE connector, turn it into an MMOD connector by moving pin 6 to pin 8, because
most modems use CD and not DSR to indicate the presence of a carrier. If not, some modems can be
programmed to provide carrier information via DSR.
●
Manufacturer-Specific Modem Initialization
Commands
Recommended initialization strings are provided here for some common modems, but be aware that Cisco
does not warrant that they are suitable or current. When in doubt, refer to the modem vendor's
documentation or technical support.
Modem Brand Initialization String Notes
(270 strony)
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