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As described in the previous chapter, you configure modem support in line configuration mode onTTY lines. When configuring modem support, there are a set of core commands everyone typicallyshould configure. These commands perform the following tasks: • Set line speed• Enable flow control on the line• Enable the modem to initiate outgoing calls or accept incoming calls You must also configure the modem itself to function with the access server. There are two ways toconfigure your modem to function with a Cisco access server: • Use the access server to automatically discover and configure common modem initialization This chapter describes the following tasks: • Attaching Modems• Configuring the Line• Configuring Modems At the end of this chapter, there is a modem configuration example. This configuration will be usedin later chapters as part of a complete sample configuration.
Attaching Modems
Before configuring lines on a Cisco access server, you must attach your modems to the asynchronousports. To attach a modem, refer to the user guide or installation guide that accompanied your accessserver.
Note Some Cisco access servers (such as the Cisco AS5200 Universal Access Server), have
integrated modems and do not require that you attach an external modem. If you have an access
server with integrated modems, you can skip this section and proceed to the section “Configuring
the Line.”
Configuring Modems 2-1
Configuring the Line
Configuring the Line
As described in the chapter “Configuring Asynchronous Lines,” you must configure the lines to
which you attach modems and allow dial-in 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> enable
2511# configure terminal
Enter 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)
After you enter line configuration mode for the lines to which your modems are attached, configurethe lines using the commands listed in Table 2-1.
Table 2-1
Required Modem Commands
speed 115200
Sets line speed to the highest common speed for the modem and the access server port. See Table 2-2 for a listof modem transmission rates and line speeds you should speed 57600
speed 38400
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.
1. Cisco Systems assumes that your modem supports flow control. Refer to your modem documentation to learn whether your modem supports flow control, and to learn the maximum transmission speed of your modem.
Table 2-2
Matching the Access Server Line Speed to Your Modem Speed
Modem Transmission Rate
Line Speed on the Access Server
To proceed with the previous example, which illustrates how to enter line configuration mode, thefollowing example shows how to configure the commands listed in Table 2-1: 2511(config-line)# speed 115200
2511(config-line)# flowcontrol hardware
2511(config-line)# modem inout
2-2 Dial Solutions Quick Configuration Guide
Configuring Modems
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 sandal2
2511(config-line)# login local
After you configure your lines, configure modem strings on the modems attached to your accessserver.
Configuring Modems
This section describes the tasks required to configure modems that are externally attached to theaccess server. This section describes the following tasks: • Communicating with Your Modem• Automatically Configuring Your Modem• Manually Configuring Your Modem• Testing the Dial-in Connection When you configure modems to function with your access server, you must provide initializationstrings 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 informationabout attaching modems.
Before you can configure the modem, you must establish communication with it, which requiresterminal access to the modem’s command environment. The process of manually configuring amodem consists of the following tasks: • Establishing a Direct Telnet Session to the Modem• Testing the Modem Connection• Suspending and Terminating Telnet Sessions Establishing a Direct Telnet Session to the Modem You communicate with the modem by establishing a direct Telnet session from the access server’sasynchronous 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).
This section explains how to establish a direct Telnet session to access the modem.
Configuring Modems 2-3
Configuring Modems
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 linenumber 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 2001
This example enables you to communicate with the modem on line 1 using the AT (attention)
command set defined by the modem vendor.
Timesaver Use the ip host configuration command to simplify direct Telnet sessions with
modems. The ip host command maps an IP address of a port to a device name.
If you are unable to connect to the modem, check the following: Issue the show users EXEC command. It should not indicate the line is in use.
Verify that the line is configured for modem inout.
Issue the show line EXEC command. The output should contain the following two lines:
Check to see if the virtual terminal connections to lines in the access server require passwords.
See the “Access Services Security” chapter for additional information about assigning passwordsto virtual terminals.
Check to see if the speed between the modem and the access server are the same. They are likelyto be different. If they are different, switch off the modem, then switch it back on. This shouldmatch the speed of the modem with the speed of the access server.
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:
Look at the output of the show line 1 command. If it displays “no CTS” for the modem hardware
state, the modem is not connected, powered on, and waiting for data, or the modem might not be
configured for hardware flow control.
Check your cabling and the modem configuration (echo or result codes might be off). Enter the
appropriate AT modem command to view the modem configuration, or enter the command at&f
to return to factory defaults. Refer to your modem documentation to learn the appropriate AT
command to view your modem configuration.
2-4 Dial Solutions Quick Configuration Guide
Configuring Modems
Suspending and Terminating Telnet Sessions 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
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. Refer to your
terminal emulator documentation for more information about escape sequences.
To suspend and then disconnect a Telnet session, perform the following steps: Suspend the Telnet session by entering Ctrl-Shift-6 x:
Enter the where EXEC command to check for open sessions:
2511# where
* 1 0 0 After suspending a session with one modem, you can connect to another modem (thensuspend it): 2511# telnet modem2
To disconnect (completely close) a session, issue the disconnect EXEC command:
2511# disconnect line 1
Closing connection to [confirm] y
Closing connection to [confirm] y
Note Before attempting to allow inbound connections, make sure you close all open connections
to the modems attached to the access server. If you have a modem port in use, the modem will not
accept a call properly.
After you have established and tested the connection to the modem, you can proceed with the nextsection “Automatically Configuring Your Modem.” Configuring Modems 2-5
Configuring Modems
The Cisco IOS software can issue initialization strings automatically for most types of modems. Amodem initialization string is a series of parameter settings that are sent to your modem to configureit to interact with the access server in a specified way. The Cisco IOS software defines seveninitialization strings that have been found to properly initialize most modems so that the modemsfunction properly with Cisco access servers. These initialization strings have the following names: • Codex_3260• Usr_courier• Usr_sportster• Hayes_optima• Global_village• Viva• Telebit_t3000 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 terminal
2511(config)# line 1 16
2511(config-line)# modem autoconfigure discovery
2511(config-line)# Ctrl-Z
2511# copy running-config startup-config
The Cisco IOS software first tries the first of these strings to see if the modem initializes properly. Ifnot, the Cisco IOS software cycles to the next string and repeats the process until the appropriatestring is found. If none of the strings properly initializes the modem, you must manually configurethe 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 theDial Solutions Command Reference. If you have access to Cisco Connection Online (CCO), you canalso access the following URL for more information: Note that these URLs are subject to change without notice.
If you cannot configure your modem automatically, you must configure it manually. The followingsections describe how to configure your externally attached modem manually: • Configuring Modem Initialization Strings• Checking Other Modem Settings• Initializing the Modem 2-6 Dial Solutions Quick Configuration Guide
Configuring Modems
This section describes how to determine the correct initialization string for your modem andconfigure 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.
Note You can use AT&F as a basic modem initialization string in most cases.
Determining the Modem Initialization String 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: • Locking the Port Speed• Setting Hardware Flow Control (RTS/CTS)• Ensuring Correct DCD Operation• Ensuring Proper DTR Interpretation• Answering Calls on the First Ring Timesaver Initialization strings for other modems are listed in the appendix “Configuring Modem
Strings and Chat Scripts” in the Dial Solutions Command Reference and on Cisco Connection
Online (CCO, formerly CIO).
Lock the speed of the modem to the speed of the serial port on the access server.
Note Make sure to turn off automatic baud rate detection, because the modem speeds must be set
to a fixed value.
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
Configuring Modems 2-7
Configuring Modems
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. Errorcorrection standards include LAPM and MNP4. V.42 error correction allows either LAPM or MNP4error correction to be negotiated. Modems differ in the way they enable error correction. Refer toyour 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. Datacompression standards include V.42 bis and MNP5. Modems differ in the way they enable datacompression. Refer to your modem documentation for the data compression settings used with yourmodem.
2-8 Dial Solutions Quick Configuration Guide
Configuring Modems
Refer to this section if you could not or chose to not initialize your modems automatically, asdescribed in the “Automatically Configuring Your Modem” section.
Once the modem initialization string has been determined, perform the following steps to configurethe modem. This example configures a U.S. Robotics Courier modem on line 1(decimal number 2000 + line number 1 = 2001): Map a host name to a decimal port. The port number is 200x, plus the number of the TTYline. The following example maps port 2001 to the IP address of the Ethernet0 interfaceon the access server ( Router(config)# ip host modem1 2001
Router(config)# exit
Establish a direct Telnet session to the modem: Router# telnet modem1
Return the modem to its factory defaults (this step is optional): at&f
Configure the modem with an initialization string. The following example string is for aU.S. Robotics Courier modem: at&b1&h1&r2&c1&d3&m4&k1s0=1
Store the modem settings in NVRAM on the modem: at&w
Note Some modems need to be “strapped” so that they start up with saved settings when powered
on, rather than using defaults. You should make sure your modem is strapped accordingly.
Suspend and disconnect your Telnet session: Router# disconnect
Closing connection to modem1 [confirm] y
Timesaver The script-reset line configuration command can automate the configuration of your
modems. See the publication Dial Solutions Configuration Guide, or the “Technical Tips” section
on CCO for more information.
Configuring Modems 2-9
Sample Modem Configuration
The access server and modem are now correctly configured for dialin access. Before configuring anyadditional protocols for the line (such as SLIP, PPP, or ARA), test the dial-in connection.
Note The same configuration issues exist between the client data terminal equipment (DTE) and
client modem. Make sure you have the correct EIA/TIA-232 cabling and modem initialization string
for your client modem.
The following is an example of a successful connection from a PC using a U.S. Robotics Couriermodem to dial in to a Cisco 2500 series access server: at&f&c1&d3&h1&r2&b1&m4&k1&w
Username: janedoe
Sample Modem Configuration
The sample configuration for this chapter configures lines 1 through 16 on a Cisco 2511 accessserver for modem control. It assumes you have a US Robotics Courier modem, which supportshardware flow control.
2511(config)# line 1 16
2511(config-line)# speed 115200
! do not enter the following command if configuring the console port 2511(config-line)# flowcontrol hardware
2511(config-line)# modem inout
2511(config-line)# modem autoconfigure discovery
2511(config-line)# modem autoconfigure type usr_courier
If you do not have one of the modems listed in the section “Automatically Configuring YourModem,” you must perform the tasks described in the following sections to configure the modem: • Establishing a Direct Telnet Session to the Modem• Testing the Modem Connection• Configuring Modem Initialization Strings• Initializing the Modem After you have configured the modems automatically or manually, test the dial-in connection, asindicated in “Testing the Dial-in Connection” to ensure you have basic connectivity beforeconfiguring your dial-in protocols.
2-10 Dial Solutions Quick Configuration Guide


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