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Because asynchronous
modems are not standard, you must write custom chat-scripts to
perform certain tasks. Chat-scripts are used for the following
tasks:
A chat-script
is
a string of text that defines the handshaking that occurs between
two DTE devices, or between a DTE and its directly attached DCE
device. It
consists of expect-send pairs that define both the string that the
local system expects to see from the remote device and the reply
that the local system should send:
(config)#chat-script
script-name expect-string send-string
For example, you can
configure chat-scripts for the following tasks:
-
Initializing the
directly attached modem
-
Instructing the
modem to dial out
-
Logging in to a
remote system
The following is a
sample chat-script
command and the Table that describes it:
(config)#chat-script
Reno ABORT ERROR ABORT BUSY "" "ATZ" OK "ATDT
\T" TIMEOUT 30 CONNECT \c
Modem-script versus System-script
Chat-scripts are used as
modem-scripts or system-scripts. Modem-scripts are used from DTE to
DCE, whereas system-scripts are sent DTE to DTE.
In the following example, the
script called Niagara is used between the router and the modem to
successfully handshake with the destination. The Gambling script is
used for logging between the router and an end-system at the
destination; the script called Niagara is used for dialing a modem:
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chat-script Niagara ABORT ERROR
"" "AT Z" OK "ATDT \T" TIMEOUT 30
CONNECT \c
!
! Script for logging into a system called Gambling and starting up
slip session:
chat-script Gambling ABORT invalid TIMEOUT 15 name: billw word:
wewpass ">" "slip default"
!
Interface async 5
dialer map ip 172.16.12.17 modem-script Niagara system-script
Gambling 918005551212
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You can manually start a
chat-script on any asynchronous line that is not currently active by
using the start-chat command, or you can configure chat-scripts so
they are executed for specific events, such as the following:
-
Line
activation-Triggered by incoming traffic (Carrier Detect signal
going up)
-
Connection-Triggered
by outgoing traffic (for example, reverse Telnet)
-
Line reset-Triggered
by async line reset
-
Startup-Triggered by
access server startup
-
Dialer-Triggered by
dial-on-demand routing (DDR)
Start-chat: Manual Start of
Chat-script
If you wish to manually start a chat-script on a line, you
can use the start-chat
privileged EXEC command.
Router#start-chat regexp
[line-number [dialer-string]]
This command provides modem-dialing
commands for a chat-script that you want to apply immediately to a
line. If you do not specify a line, the script runs on the current
line. If the specified line is already in use, the script is not
activated, and an error message appears.
The argument regexp is used to
specify the name of the modem script that is to be executed. The
first script that matches the argument in this command and the dialer
map command will be used.
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