Application module interface for a control channel in a private branch exchange (pbx) environment

Abstract

An application module interface (AMI) allows one or more modules to access voice or data channels in a private branch exchange (PBX) environment. The AMI provides a control channel that allows a module to obtain and vary the status and configuration of a telephone terminal and permits communications with the application module(s) connected to a telephone terminal. A frame format includes, for example, a start bit (logic “1”), three control channel bits, C, and eight stop bits (logic “0”). The control channel field, C, bits include one flag bit and two data bits. A complete control channel data word is split, for example, over five consecutive AMI frames and contains, for example, a total of nine data bits and a parity bit, transmitted least significant data bit first. The parity bit creates “even parity” for the ten total bits. The flag bit is set to one to indicate the start of a new control channel word, or zero otherwise. An “invalid data” error is detected by a control channel receiver when the flag bit contains a one in two or more out of five consecutive frames. Messages may be of two types, namely, an application message or a protocol control message. The protocol control messages are single word messages used for acknowledgement and link activity. The application messages come in various lengths and convey information, events and requests. An RS-232 (passageway) or a Universal Serial Bus module allows a personal computer or other enabled device to interact with and control the operation of a telephone terminal for computer telephony integration (CTI) applications.