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d.fm:090019e98070645b:37211:Suspending and Terminating Telnet Sessions
You communicate with the modem by establishing a direct Telnet session from AccessPath-TS3 system asynchronous lines to the modem.
Note This process is also referred to as reverse Telnet. The term reverse Telnet means that you are initiating a Telnet session out the asynchronous line, instead of accepting a connection into the line (which is a forward connection).
To establish a direct Telnet session to a modem, determine the IP address of your LAN (Ethernet) interface, and then enter a Telnet command to port 2000 + n on the System Controller, where n is the line number to which the modem is connected. For example, to connect to the modem attached to line 129, enter the following command from an EXEC session on the System Controller:
This example enables you to communicate with the modem on line 129 using the AT (attention) command set defined by the modem vendor.
If you are unable to connect to the modem, check the following:
After you make a direct Telnet connection to the modem, you need to test the connection. Send the modem the AT command to request its attention. It should respond with OK. For example:
If the modem does not reply to the AT command, check the following:
The direct Telnet session must be terminated before the line can accept incoming calls. If you do not terminate the session, it will be indicated in the output of the show users command when it returns a modem state of ready if the line is still in use. If the line is no longer in use, the output of the show line value command will return a state of idle.
Terminating the Telnet session requires first suspending it, then disconnecting it. To suspend a Telnet session, enter the escape sequence Ctrl-Shift-6 x (press Control-Shift-6, let go, then press x). Enter the disconnect EXEC command to terminate the Telnet session.
Note Ensure that you can reliably issue the escape sequence to suspend a Telnet session. Some terminal emulator packages have difficulty sending the Ctrl-Shift-6 x sequence. See your terminal emulator documentation for more information about escape sequences.
To suspend and then disconnect a Telnet session, perform the following steps:
Step 2 Enter the where EXEC command to check for open sessions:
Step 3 After suspending a session with one modem, you can connect to another modem (then suspend it):
Step 4 To disconnect (completely close) a session, issue the disconnect EXEC command:
Note Before attempting to allow inbound connections, make sure you close all open connections to the modems attached to the AccessPath-TS3 system. If you have a modem port in use, the modem will not accept a call properly.
The following sections describe how to configure an externally attached modem:
This section describes how to determine the correct initialization string for your modem and configure your modem with it.
Modem command sets vary widely. Although most modems use the Hayes command set (prefixing commands with AT), Hayes-compatible modems do not use identical AT command sets.
See your modem manufacturer's documentation to learn how to examine the current and stored configuration of the modem you are using. Generally, you enter AT commands such as &v, i4, or *o to view, inspect, or observe the settings.
A sample modem initialization string for a Microcom modem is as follows:
The modem initialization strings enable the functions defined in the following sections:
Timesaver Initialization strings for other modems are listed in the appendix "Configuring Modem Strings and Chat Scripts" in the Access Services Command Reference and on Cisco Connection Online (CCO) in Tech Tips (http://www.cisco.com/kobayashi/Tech_root.shtm). Note that these URLs are subject to change without notice. |
Lock the speed of the modem to the speed of the auxiliary port on the System Controller.
Note Make sure to turn off automatic baud rate detection because the modem speeds must be set to a fixed value.
Modems differ in the method they use to lock the EIA/TIA-232 (serial) port speed. In the modem documentation, vendors use terms such as, port-rate adjust, speed conversion, or buffered mode. Enabling error correction often puts the modem in the buffered mode. See your modem documentation to see how your modem locks speed (check the settings &b, \j, &q, \n, or s-register settings).
Ready To Send (RTS) and Clear To Send (CTS) signals must be used between the modem and the System Controller to control the flow of data. Misconfiguring flow control for software or setting no flow control can result in hung sessions and loss of data. Modems differ in the method they use to enable hardware flow control. See your modem documentation to see how to enable hardware flow control (check the settings ', &e, &k, &h, &r, or s-register).
The modem must use the data carrier detect (DCD) wire to notify the System Controller when a session has been negotiated and is established with a remote modem. Most modems use the setting &c1. See your modem documentation for the DCD settings used with your modem.
The modem must interpret a toggle of the data terminal ready (DTR) signal as a command to drop any active call and return to the stored settings. Most modems use the settings &d2 or &d3. See your modem documentation for the DTR settings used with your modem.
If a modem is used to service incoming calls, it must be configured to answer a call after a specific number of rings. Most modems use the setting s0=1 to answer the call after one ring. See your modem documentation for the settings used with your modem.
This section defines other settings that might be needed or desirable depending on your modem.
Error correction can be negotiated between two modems to ensure a reliable data link. Error correction standards include LAPM and MNP4. V.42 error correction allows either LAPM or MNP4 error correction to be negotiated. Modems differ in the way they enable error correction. See your modem documentation for the error correction methods used with your modem.
Data compression can be negotiated between two modems to allow for greater data throughput. Data compression standards include V.42 bis and MNP5. Modems differ in the way they enable data compression. See your modem documentation for the data compression settings used with your modem.
After the modem initialization string has been determined, perform the following steps to configure the modem. This example configures a Microcom modem on line 129 (decimal number 2000 + line number 129 = 2129):
Step 2 Establish a direct Telnet session to the modem:
Step 3 Optionally, return the modem to its factory defaults:
Step 4 Configure the modem with an initialization string. The following example string is for a Microcom modem:
Step 5 Store the modem settings in NVRAM on the modem:
Note Some modems need to be "strapped" so that they start up with saved settings when powered on, rather than using defaults. Make sure your modem is strapped accordingly.
Step 6 Suspend and disconnect your Telnet session:
Posted: Tue Jan 21 04:28:10 PST 2003
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