Sometimes you may find that KPPP has difficulties hanging up the modem. This is likely the result of a mismatch between KPPP settings and those of the modem. A standard modem uses two methods to decide to hangup: Command, and DTR. The Command method involves sending an escape sequence to the modem, which puts it in command mode, then issuing the hangup command (ATH).
Outside of KPPP, when configuring the pppd package manually, it's often helpful to use the command method, so that one can exit a terminal session, and then start pppd without having the modem hangup. In most other situations, the DTR method is preferred, as it is simpler.
The DTR method will have the modem hangup whenever KPPP stops using the modem. If you obtain a modem session, and query the state via AT&V, and you can see among the displayed settings for the active profile a &D0, then the DTR hangup method is disabled. To enable the DTR method, use the button to get a modem session, then:
ATZ# reset to default profile
AT&D2# Set to hang up on DTR drop
AT&W# Write to default profile
Whenever the Data Terminal Ready (DTR) line on the serial line between the host computer and the modem goes high, the modem hangs up. When KPPP opens the serial port, the DTR line is pulled low, on an external modem, you can see the DTR (or TR) light come on when this happens. When the TR light goes out (because KPPP has closed the serial port, or something worse!), the modem will hangup.
The other way to have a modem hang up when connected (used when
n is not 2) is to have the
modem accept the command when a session is in progress. To have it hang up
properly, get a modem session, and set the guard time to a short interval like
Then use the Guard Time slider in the Modem commands
section to match the register (
S12 to this value
5. The modem should then hangup properly.
When the local modem is connected to a remote modem, it is in the “connect” state, where it passes all characters it receives to the remote modem without interpretation. To have the modem accept the characters as commands for itself, one must put the modem into the command state. The escape code does this.
The escape code is defined as being three intervals of time whose length
is defined by
S12 in fiftieths of a second.
Quiet (must last more than
Escape character (defined by the register
S2, the default is “+”), repeated three times (less than
S12/50 seconds between each.
Quiet (must last more than
Once the modem is in the command state, you can send it commands. To have it hang up, send the command ATH. The escape codes and the hangup string used by KPPP are shown in the Modem Commands dialog. These should match your modem.