Content-type: text/html Man page of modem


Section: Environments, Tables, and Troff Macros (7)
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modem - Describes guidelines for using modems  


The Digital UNIX system enables you to use a variety of modems for point-to-point connections to systems that are not in close proximity to each other. These connections can be Serial Line Internet Protocol (SLIP), Point-to-Point Protocol (PPP), and UNIX-to-UNIX Copy Program (UUCP) connections. In addition, these connections can be basic dial-out/dial-in connections (for example, to log in to a remote system to perform remote system administration).

This section presents general guidelines for using modems on Digital UNIX systems for all types of connections. See Network Administration for specific information on SLIP, PPP, and UUCP connections.  

Using the Correct Modem Cables

In order to connect a modem to the serial port of your system, you must use the correct cable. If you do not, your software may not function properly. The following table lists the cables you should use. The cable connector is either 25-pin or 9-pin, depending on the type of serial port on your system. See the hardware documentation for your system if you are unsure about the type of serial port.


OPEN DECconnect cables do not provide a sufficient number of wires for full modem control. Digital recommends that you do not use them for connecting modems to the system.

Cable NumberDescription

BC22E-xx16-wire modem cable (Male DB25 pin to female DB25 pin cable)
BC22F-xx25-wire modem cable (Male DB25 pin to female DB25 pin cable)
BC29P-xxMale DB25 pin to female DB9 pin cable
PC modem cableMale DB25 pin to female DB9 pin cable

In the previous table, xx denotes the cable length. For example, BC22E-10 is a ten-foot cable.  

Configuring a System for Dial-In Access

After you have obtained the correct cable and connected your modem to it and the telephone network, do the following: Edit the /etc/remote file and create an entry similar to the kdebug entry. For example, if your modem is connected to tty00 and you are going to use a baud rate of 38,400 to access the modem, create an entry similar to the following: b38400:dv=/dev/tty00:br#38400:pa=none


Some modems set their baud rate to the serial port rate. Be sure to access the modem using the same baud rate that you are going to specify to getty or uugetty. Otherwise, you might not be able to log in because of a mismatch in baud rates.

See modem(7) if you are unsure which port your modem is connected to. Use the tip command to access the modem as follows: tip b38400
The tip utility responds with a connected message. You can now communicate with the modem. If your modem is using the AT command language, enter the following command: at<Return>
If the modem is not in quiet mode, it responds with an OK message. Set the modem up for dial-in access. The following table lists the AT commands required. Most of these command settings are the default settings.


at&c1Normal Carrier Detect (CD) operation. Tells the modem to not
raise Carrier Detect until it see Carrier Detect from the other
at&d2Normal Data Terminal Ready (DTR) operation. This is
important in that it tells the modem to hang up the line when
DTR drops. For example, when the user logs off the system.
atq1Sets the modem into quiet mode. Result codes are not sent to
the system.
ate0Echo off. This prevents the modem from echoing the login
prompt issued by the getty process.
ats0=nSpecifies the number of rings to wait before answering. If
n = 0 (zero), the modem will not answer.
at&w0Saves the current modem settings in NVRAM.
Digital UNIX supports both hardware and software flow control. If the system supports hardware flow control, set the modem and the serial line up to use hardware flow control by using the appropriate commands. If hardware flow control is not supported, you should use software flow control. Hardware flow control is recommended for speeds greater than 19,200 bits per second (bps). Edit the /etc/inittab file and create an entry for the modem. If you want to use the modem line in non-shared mode, create an entry similar to the following: modem:23:respawn:/usr/sbin/getty /dev/tty00 M38400 vt100
If you want to use the modem line in shared mode (for dial-out and dial-in connections), use uugetty instead of getty and create an entry similar to the following: modem:23:respawn:/usr/lib/uucp/uugetty -r -t 60 tty00 38400
With uugetty, you will be able to use the tip and cu utilities, but might not be able to use third-party utilities because of differences in file locking.

If you want to use the uugetty utility, you must install the UNIX-to-UNIX Copy Facility subset.

As root, start the getty or uugetty process by entering the following command: init q

The getty or uugetty process starts, then goes to sleep, waiting for someone to dial into the system.

Configuring Your System for Dial-Out Access

After you have obtained the correct cable and connected your modem to it and the telephone network, do the following: Verify that there is an entry for the modem name specified with the modemtype subcommand in the /etc/acucap file. If your modem does not have an entry in the /etc/acucap file, do the following: Copy an entry similar to that of your modem. The following entry is for a US Robotics modem for use in shared mode with tip: us|US|US Robotics (28.8 fax/data modem):\

Be sure the entry includes at least the AT commands in the following table. The other modem settings can remain as they are.


ate1Turns on echoing.
atq0Displays the result codes.
Modify the modem attributes to match your modem's attributes and include the debug option (db). With debugging turned on, the modem will provide you with additional information with which to tune the modem attributes in the file. See acucap(4) for more information. Create an entry in the /etc/remote for the system you want to call. Among the information you can supply is the Digital UNIX device, baud rate, and /etc/acucap that defines your modem. The following two entries are for the modem specified in step 1a. tip38400:tc=us38400 us38400|38400 Baud dial out via US Robotics modem:\
In the previous example, the first line is an entry that points to the us38400 entry specifying shared capabilities for modems. The second line is the first line of the us38400 entry. The third line defines end-of-line characters, and input and output end-of-file marks. The fourth line defines the UNIX device to open for the connection, the baud rate, the parity, the name of the /etc/acucap file entry, and the dial-up line.
See remote(4) for more information. If you use getty to provide access to the system from a modem and a getty process is already running, do the following: Edit the /etc/inittab file and put a comment character (#) at the beginning of the modem entry. Issue the init q command to terminate the getty process. Use the tip command, specifying the -baud_rate flag and the telephone number to dial out as follows: tip -38400 8881234
In this example, tip strips off the minus sign (-) from the baud rate and concatenates the tip command name and the baud rate to create the string tip38400. Then, tip searches the /etc/remote file for the entry matching the string. The entry in the /etc/remotes file, points the capability information in the us38400 entry to initialize the modem.
By specifying the telephone number on the command line, you can share the same modem attributes for outgoing connections that have different telephone numbers.
When you log off the remote system and exit tip, the modems saved settings are restored, readying the modem for the next user. If used in shared mode, the modem is available for dial-in access.


Commands: cu(1), tip(1), getty(8), uugetty(8).

Files: acucap(4), inittab(4), remote(4).

Devices: ports(7).

Network Administration delim off



Using the Correct Modem Cables
Configuring a System for Dial-In Access
Configuring Your System for Dial-Out Access

This document was created by man2html, using the manual pages.
Time: 02:40:24 GMT, October 02, 2010