Installing and Administering PPP

154 Appendix A
Modem Connections
Dial Up Modems
If you configure for software control, make sure both ends of the PPP
connection have the 0x000A0000 bits turned on in their asynchronous
control character map (asyncmap). This is the default for PPP. A
computer and modem using software flow control can talk to a computer
and modem using hardware flow control, but both ends must have the
asyncmap set to accommodate software flow control.
Modem Commands
Most modems are intelligent and recognize commands sent to them by
the system during DTE to DCE transmission. Commands are different
than signals exchanged by the DTE and DCE, like RTS and CTS.
Generally, signals indicate the state of the DTE or DCE. Commands tell
the modem to perform special tasks or modify dialing procedures.
Common commands cause the modem to answer an incoming call, use
touch tone dialing, terminate the current connection, or pause before
sending the next number in a string. The modem recognizes system
commands because they are preceded by the characters AT. Therefore,
the commands are referred to as the AT command set.
Common
Commands
Description
A Answer incoming call; overrides S0 register.
En Echo command; E0 disables echo to monitor; E1
enables echo.
Hn Switch hook control; H0 hangs up; H1 goes on-line.
O Switch from command mode to data mode.
Xn Select call progress code set.
&Cn Select Carrier Detect option.
&Fn Load factory setting number n.
&V List modem's stored configuration files.