PPP Server Configuration

Configuring a server to callback a client is desirable for companies who want the phone bill charged to their account versus the client (employee) who may be in a hotel room where long-distance rates are high.

You must first configure mgetty to work as a regular dialin server and a regular dialin PPP server before you configure the callback procedures. After the PPP server is running well, you are ready to procede with the callback configuration.

Server Configuration

To enable callback on a server, you have to edit only two files. First create a file /etc/mgetty+sendfax/callback.conf and we leave it empty. Next we edit /etc/mgetty+sendfax/login.conf and add line:

	call - - /usr/sbin/callback - S 123456

Where call is a pseudo-user needed to initiate the connection. The line in the login.conf puts in motion the program calling the given number (in this case it's 123456). The same procedures can be applied to other users. When we call a server, it asks us to give verification. We login as pseudo-user, in this case it calls the script in our computer hangs up the modem. We wait and the connection is cut off. The program call-back starts working and recalls us. We verify ourselves again as pppuser with password. We combine the connection and interface ppp.

Workstation (client) Configuration

The configuration of workstations is very simple. When you have MS Windows, you have to install dial-up for your number. In the modem properties we add into the extra options field:

	&c0s0=1

For a Microsoft Windows client to authenticate the call, you must understand how dialup scripting works (and how to add the script option to the dialup networking connection). Add the following code to the dialup networking connection's script:

	proc main
		delay 1
		waitfor "ogin:"
		transmit "call^M"
		waitfor "RING"
		transmit "ATA^M"
		waitfor "CONNECT"
		waitfor "ogin:"
		transmit "pppuser^M"
		waitfor "word:"
		transmit "ppp^M"
	endproc

Notice that after the login prompt in the script above, we use the word "call" and then wait for the modem to return the "RING" command. The word call corresponds to word call in the login.conf file. Had we used any other word in the login.conf file, we would have used it in the script above. Since the terminal waits for the modem to return the "RING" command, the server must have hung-up on us. The script is waiting for the serve to call back so that it can continue the script and authenticate.

For a linux client to authenticate the callback, add the following lines to the option file (you may use a modem specific options file such as options.ttyS1):

	lock
	defaultroute
	noipdefault
	modem
	33600
	crtscts
	debug
	passive
	asyncmap 0

The dialing script:

	#!/bin/bash
	killall -INT pppd 2>/dev/null
	rm -f /var/lock/LCK* /var/run/ppp*.pid
	(/usr/sbin/pppd -detach call ppp_call &) || exit 1
	exit 0

Use the following chatscript to initiate the first call:

	TIMEOUT 5
	ABORT 'ERROR'
	ABORT 'BUSY'
	ABORT 'NO ANSWER'
	ABORT 'NO DIALTONE'
	ABORT '\nVOICE\r'
	ABORT '\nRINGING\r\n\r\nRINGING\r'
	'' AT&FH0 'OK-+++\c-OK' 'AT&C0S0=1'
	TIMEOUT 40
	OK ATDT5376443 CONNECT ''
	ogin:-ogin: ppp-pseudo-user
	'\nNO CARRIER\r' ''
	TIMEOUT 180
	'\nRING\r' AT&C1A
	CONNECT ''
	TIMEOUT 20
	ogin:-ogin: pppuser
	sword:-sword password_for_ppuser