Importance

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Abstract

A system and method transmits digitalized voice and data over a communications channel as a combined data stream while transmitting the digitalized voice in substantially real-time. The system makes use of a redundancy in the coding used to represent at least one amplitude level in the digitalized voice by using one of the redundant codings as a signalling code in a signalling time frame to signal the presence of data and by converting a digitalized voice codeword having this redundant code to its duplicate code. In this manner, during silence periods of the voice communication on the communications channel, data may be inserted. The system and method allow digital data to be transmitted without any limitation on its bit density. As the communications channel normally has a bit density requirement requiring at least a certain density of digital ones, the system of the present invention monitors the digitalized data to determine when the number of consecutive zeros exceeds a predetermined number and inserts a one into the data stream to insure that bit density requirements are not violated. The receiver tests for the signalling code indicative of the presence of data and based on this code, transmits the data and voice to their respective proper locations at the downstream end of the communications channel. Later, the receiver removes any inserted ones from the digital data stream to recover the digital data.

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First Claim