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modem(7)
NAME
modem - Describes guidelines for using modems
DESCRIPTION
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.
Note
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.
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Cable Number Description
_____________________________________________________________________________
BC22E-xx 16-wire modem cable (Male DB25 pin to female DB25 pin cable)
BC22F-xx 25-wire modem cable (Male DB25 pin to female DB25 pin cable)
BC29P-xx Male DB25 pin to female DB9 pin cable
PC modem cable Male 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:
1. 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
Note
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.
2. 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.
3. 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.
4. 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.
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Command Description
_________________________________________________________________________
at&c1 Normal Carrier Detect (CD) operation. Tells the modem to not
raise Carrier Detect until it see Carrier Detect from the other
modem.
at&d2 Normal 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.
atq1 Sets the modem into quiet mode. Result codes are not sent to
the system.
ate0 Echo off. This prevents the modem from echoing the login
prompt issued by the getty process.
ats0=n Specifies the number of rings to wait before answering. If
n = 0 (zero), the modem will not answer.
at&w0 Saves 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).
5. 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.
Note
If you want to use the uugetty utility, you must install the UNIX-to-
UNIX Copy Facility subset.
6. 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:
1. 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:
a.
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):\
:cr:hu:ls:re:ss=AT\rATE1Q0&C0X0&A0\r:sr=OK:\
:sd#250000:di=ATD:dt=\r:\
:dd#50000:fd#50:os=CONNECT:ds=\d+++\dATZ\r\dATS0=2\r:\
:ab=\d+++\dATZ\r\dATS0=2:
Be sure the entry includes at least the AT commands in the following
table. The other modem settings can remain as they are.
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Command Description
____________________________________
ate1 Turns on echoing.
atq0 Displays the result codes.
b.
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.
2. 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:\
:el=^U^C^R^O^D^S^Q@:ie=#%$:oe=^D:\
:dv=/dev/tty00:br#38400:ps=none:at=us:du:
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.
3. If you use getty to provide access to the system from a modem and a
getty process is already running, do the following:
a.
Edit the /etc/inittab file and put a comment character (#) at the
beginning of the modem entry.
b.
Issue the init q command to terminate the getty process.
4. 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.
RELATED INFORMATION
Commands: cu(1), tip(1), getty(8), uugetty(8).
Files: acucap(4), inittab(4), remote(4).
Devices: port(7).
Network Administration