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As described in the previous chapter, you configure modem support in line configuration mode on TTY lines. When configuring modem support, there are a set of core commands everyone typically should configure. These commands perform the following tasks:
You must also configure the modem itself to function with the access server. There are two ways to configure your modem to function with a Cisco access server:
This chapter describes the following tasks:
At the end of this chapter, there is a modem configuration example. This configuration will be used in later chapters as part of a complete sample configuration.
Before configuring lines on a Cisco access server, you must attach your modems to the asynchronous ports. To attach a modem, refer to the user guide or installation guide that accompanied your access server.
As described in the chapter "Configuring Asynchronous Lines," you must configure the lines to which you attach modems and allow dialin access. To configure lines, enter line configuration mode for the specific lines you need to configure. The following example shows lines 1 through 16 being configured on a Cisco 2511 access server (remember, bold screen font indicates what you type):
2511>enablePassword: 2511#configure terminalEnter configuration commands, one per line. End with CNTL/Z. 2511(config)#line 1 X (X = the highest number of lines the router has; 8 or 16)2511(config-line)#
After you enter line configuration mode for the lines to which your modems are attached, configure the lines using the commands listed in Table 2-1:
| Command | Purpose |
|---|---|
| speed 115200
or speed 57600 or speed 38400 | Sets line speed to the highest common speed for the modem and the access server port. See Table 2-2 for a list of modem transmission rates and line speeds you should set on the access server. 1 |
| flowcontrol hardware | Sets RTS/CTS flow control on the line. |
| modem inout | Configures the line to drop the connection when the carrier detect (CD) signal is lost (cycle DTR to close the connection). The modem dialin command can be used instead of the modem inout command to enhance security because the modem dialin command restricts outgoing connections from the access server to the modem. Use the modem inout command during setup so that you can configure the modem from the access server, and change to the modem dialin command when testing is completed. |
| Modem Transmission Rate | Line Speed on the Access Server |
|---|---|
| 9600 | 38400 |
| 14400 | 57600 |
| 28800 | 115200 |
To proceed with the previous example, which illustrates how to enter line configuration mode, the following example shows how to configure the commands listed in Table 2-1:
2511(config-line)#speed 1152002511(config-line)#flowcontrol hardware2511(config-line)#modem inout
The preceding examples configure your lines (1 to 8 or 16) to support modems.
For testing purposes, enter a password and login local command, though you remove these later:
2511(config-line)#password sandal22511(config-line)#login local
After you configure your lines, configure modem strings on the modems attached to your access server.
This section describes the tasks required to configure modems that are externally attached to the access server. This section describes the following tasks:
When you configure modems to function with your access server, you must provide initialization strings and other settings on the modem to tell it how to function with the access server.
This section assumes you have already physically attached the modem to the access server. If not, refer to the user guide or installation and configuration guide for your access server for information about attaching modems.
Before you can configure the modem, you must establish communication with it, which requires terminal access to the modem's command environment. The process of manually configuring a modem consists of the following tasks:
You communicate with the modem by establishing a direct Telnet session from the access server's asynchronous lines to the modem.
This section explains how to establish a direct Telnet session to access the modem.
To establish a direct Telnet session to a modem, determine the IP address of your LAN (Ethernet) interface, then enter a Telnet command to port 2000 + n on the access server, where n is the line number to which the modem is connected. For example, to connect to the modem attached to line 1, enter the following command from an EXEC session on the access server:
Router# telnet 172.16.1.10 2001
Trying 172.16.1.10, 2001 ... Open
This example enables you to communicate with the modem on line 1 using the AT (attention) command set defined by the modem vendor.
If you are unable to connect to the modem, check the following:
Modem state: Idle Modem hardware state: CTS noDSR DTR RTS
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:
at
OK
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.
To suspend and then disconnect a Telnet session, perform the following steps:
Step 1 Suspend the Telnet session by entering Ctrl-Shift-6 x:
- suspend keystroke -
Step 2 Enter the where EXEC command to check for open sessions:
where
Step 3 After suspending a session with one modem, you can connect to another modem (then suspend it):
telnet modem2
- suspend keystroke -
Step 4 To disconnect (completely close) a session, issue the disconnect EXEC command:
disconnect line 1
y
y
After you have established and tested the connection to the modem, you can proceed with the next section "Automatically Configuring Your Modem."
The Cisco IOS software can issue initialization strings automatically for most types of modems. A modem initialization string is a series of parameter settings that are sent to your modem to configure it to interact with the access server in a specified way. The Cisco IOS software defines seven initialization strings that have been found to properly initialize most modems so that the modems function properly with Cisco access servers. These initialization strings have the following names:
If you do not know which of these modem strings is appropriate for your modems, issue the modem autoconfigure discovery line configuration command, as shown in the following example:
2511#configure terminal2511(config)#line 1 162511(config-line)#modem autoconfigure discovery2511(config-line)#Ctrl-Z2511#copy running-config startup-config
The Cisco IOS software first tries the first of these strings to see if the modem initializes properly. If not, the Cisco IOS software cycles to the next string and repeats the process until the appropriate string is found. If none of the strings properly initializes the modem, you must manually configure the modem (refer to "Manually Configuring Your Modem" later in this chapter).
If you know that your modem can be configured using an initialization string from one of these scripts, you can issue the modem autoconfigure type type command, where type is one of the strings in the preceding list. If you list a specific modem type, initialization proceeds more quickly.
The following example shows how to enter line configuration mode and issue the modem autoconfigure type type command for a US Robotics Sportster modem.
2511(config-line)# modem autoconfigure type usr_sportster
For more information about the recommended strings for any type of modem, refer to the section "Sample Modem Strings" in the appendix "Configuring Modem Support and Chat Scripts" in the Access Services Command Reference. If you have access to Cisco Connection Online (CCO), you can also access the following URL for more information: http://www.cisco.com/warp/customer/76/4.html
Note that these URLs are subject to change without notice.
If you cannot configure your modem automatically, you must configure it manually. The following sections describe how to configure your externally attached modem manually:
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.
Refer to 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 US Robotics Courier modem is as follows:
&b1&h1&r2&c1&d3&m4&k1s0=1
The modem initialization strings enable the functions defined in the following sections:
 | Time Saver 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, formerly CIO) 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 serial port on the access server.
The port speed must not change when a session is negotiated with a remote modem. If the speed of the port on the access server is changed, you must establish a direct Telnet session to the modem and send an AT command so that the modem can learn the new speed.
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. Refer to 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 access server 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. Refer to 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 indicate to the access server when a session has been negotiated and is established with a remote modem. Most modems use the setting &c1. Refer to 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. Refer to 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. Refer to 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. Refer to 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. Refer to your modem documentation for the data compression settings used with your modem.
Refer to this section if you could not or chose to not initialize your modems automatically, as described in the "Automatically Configuring Your Modem" section.
Once the modem initialization string has been determined, perform the following steps to configure the modem. This example configures a U.S. Robotics Courier modem on line 1 (decimal number 2000 + line number 1 = 2001):
Step 1 Map a host name to a decimal port. The port number is 200x, plus the number of the TTY line. The following example maps port 2001 to the IP address of the Ethernet0 interface on the access server (172.16.1.10):
ip host modem1 2001 172.16.1.10
exit
Step 2 Establish a direct Telnet session to the modem:
telnet modem1
Step 3 Return the modem to its factory defaults (this step is optional):
at&f
Step 4 Configure the modem with an initialization string. The following example string is for a U.S. Robotics Courier modem:
at&b1&h1&r2&c1&d3&m4&k1s0=1
Step 5 Store the modem settings in NVRAM on the modem:
at&w
Step 6 Suspend and disconnect your Telnet session:
The access server and modem are now correctly configured for dialin access. Before configuring any additional protocols for the line (such as SLIP, PPP, or ARA), test the dialin connection.
The following is an example of a successful connection from a PC using a U.S. Robotics Courier modem to dial in to a Cisco 2500 series access server:
at&f&c1&d3&h1&r2&b1&m4&k1&w
OKatdt9,5551234CONNECT 14400/ARQ/V32/LAPM/V42BIS User Access Verification Username:janedoePassword: Router>
The sample configuration for this chapter configures lines 1 through 16 on a Cisco 2511 access server for modem control. It assumes you have a US Robotics Courier modem, which supports hardware flow control.
2511(config)#line 1 162511(config-line)#speed 115200! do not enter the following command if configuring the console port 2511(config-line)#flowcontrol hardware2511(config-line)#modem inout2511(config-line)#modem autoconfigure discovery2511(config-line)#modem autoconfigure type usr_courier
If you do not have one of the modems listed in the section "Automatically Configuring Your Modem" on page 2-6, you must perform the tasks described in the following sections to configure the modem:
After you have configured the modems automatically or manually, test the dial-in connection, as indicated in "Testing the Dialin Connection" on page 2-9 to ensure you have basic connectivity before configuring your dialin protocols.
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