# Interpreting line interface signaling

This section describes how to interpret signaling to and from the following AG 2000 line interfaces:

- Loop start

- Subscriber loop

- DID

The telephony protocol, embodied by a TCP running on the AG 2000 board, automatically controls and monitors the line signaling bits. This information is provided for reference only. Controlling the signaling bits manually may violate local telecommunications regulations.

The following table describes the two signaling directions:

Signaling type | Description
--- | ---
Transmit | The signaling that the board sends out onto the phone line through the line interface. The transmit signal is used to control the line or phone.
Receive | This signaling comes from the phone line through the line interface to the board. An application can monitor this signal to detect loop current or ringing.

The line interfaces on the board convert the signaling into the line condition appropriate for the line type (for example, loop start). They also convert incoming information into digital signals recognizable by AG 2000-based applications.