Communication system for converting ISDN signaling protocol between local and public network having first group of mandatory elements and second group of non-mandatory elements

摘要

A communication system operates compatibly with a public or private switching network using a Q.931 protocol for basic rate ISDN communications. Communications between a control unit and station terminals of the system use a local protocol which is a modification of the Q.931 protocol. This local protocol includes one segment including the mandatory elements of the Q.931 protocol and a second segment derived by converting the optional elements of the Q.931 protocol into a local codeset which controls the user interface circuits at each station terminal. The local protocol enables call control between the control unit and each station terminal to be managed on a bearer channel basis while call control between the system and the network is managed on a call appearance basis using the standard Q.931 protocol. The local protocol provides for communicating line selection and feature activation commands from the terminal to the control unit, using simple button commands.