# Line interface signaling modules

Line interface signaling modules are available for the AG 2000 board. A line interface signaling module is a circuit that connects a bidirectional transmission channel to separate receive and transmit channels. Each line interface signaling module has four ports. Two line interface signaling modules can fit on an AG 2000 board. This allows you to monitor and control at least eight channels of signaling information. The following illustration shows where the line interface signaling modules attach to an AG 2000 board:

Do not change the settings on the line interface signaling modules or attempt to remove the modules. They are factory installed and tested.

The following AG 2000 line interfaces are available:

- Loop start

- Subscriber loop

- Direct Inward Dialing (DID)

## Loop start interface

The loop start interface replaces a telephone, modem, or fax machine at the end of a standard telephone line or PBX extension.

The loop start interface can also be a trunk interface to the telephone network. With loop start trunks, you can segregate incoming calls from outgoing calls to avoid collisions between the two.

There are two loop start interface models:

Loop start interface model | Conforms to...
AG 2000 L | North American, most Asian, and most Latin American regulations.
AG 2000 LE | The European CTR-21 regulation.

Changing the interface model has no impact on applications you have already written.

The loop start interface:

- Is certified in North America and in EU countries.

- Has very high tolerance to common mode power line interfaces.

- Detects loop current reversals and interruptions in the off-hook mode.

- Receives Called Parity Identification in some countries.

- Records calls in on-hook mode where permitted by regulations.

## Subscriber loop interface

The subscriber loop interface connects to telephones, modems, or fax machines.

Unlike other station interfaces that can be limited to 2,000 or 3,000 feet (600 or 900 m) of cable, the subscriber loop interface can support a single telephone up to 18,000 cable feet (15 km) away as long as the loop resistance is less than 1500 Ohms.

The subscriber loop interface provides the loop current and ring voltage for signaling and powering the telephone. Therefore, it requires a ringing power supply. Refer to Subscriber loop power supply for more information.

## Direct Inward Dialing (DID)

The DID interface attaches to the telephone network for incoming calls and supports receiving dialed digits with each call. These digits can be used by a PBX to route calls to the desired extension and to route received faxes. The DID interface requires special service from the telephone network and a block of received telephone numbers. The DID interface requires a power supply. Refer to DID power supply for more information.

The other end of the DID trunk can be an AG 2000 loop start interface. However, a TCP for that is not offered.

DID is not available in EU countries.