# Modem Tricks and Hints

This section should get the fearful started on the (not so) arcane art of modem tweaking. The commands here are all Hayes AT standard, but all modems are not equal, so your mileage may vary.

## Modem Sessions

A Modem session allows you to interact with the modem directly. You type commands, and it will respond. To obtain a modem session, when no connection is active, open the Configure &kppp; dialog, select to edit a modem and then click the Terminal button on the Modem tab. This will open a window for interactive configuration of the modem. Try typing ``ATZ`` (which resets your modem) Your should get an OK response. Use File Close to end the session.

## Modem Profiles

One reason you might want to send the modem commands directly is if you have a set of modem configurations you want to keep, and not have to specify for every connection. A good way to do that is via modem profiles. Modems can have several stored profiles numbered 0,1,... `AT&V` can be used to view them all. The default profile is usually 0 (this can be changed via `AT&Y`.) The profile currently in use is called the active profile.

When you change a setting, the active profile is modified. The `ATZ` command will have the modem load the default profile, erasing any changes you have made. To save changes, Load the profile you want to change via `ATZ`n`` (where `n` is the profile number). Make the changes you want, then save it with `AT&W`n``. To have kppp use the profile you want, change the modem initialization string (Modem Commands Initialization String on the Modem tab). For example `ATZ1` will have the kppp reset the modem and use stored profile #1.

If you want reset you modem to get back to some known starting point, use `AT&F&W` to set the active profile to the factory defaults, and store those settings as the default profile.

Examples of profile changes are in the next section

## Getting the modem to hang up

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.

### DTR (`AT&Dn`) method

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 Terminal 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

#### How the DTR method works

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.

### Command method

The other way to have a modem hang up when connected (used when `AT&D`n`` where `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 so:

    ATZ
    ATS12=5
    AT&W

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.

#### How the Command Method Works

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 `S12`/50 seconds)

- 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 `S12`/50 seconds)

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.

## Make Tone dialing faster

If you can use tone dialing, the amount of time it takes to dial can be changed using the `S11` register. It gives the duration (in 100hundreds of a second) to send each tone while dialing. The default is usually 95 (almost a second.) How fast you can dial depends on the phone company's switching equipment which handles your line. The minimum duration is 50, almost twice as fast, and that speed often works.

    ATZ        # reset to default profile
    ATS11=50   # fastest possible dialing, use a higher number if it doesn't work
    AT&W   # write to default profile