Rolm Corporation

John D Edwards

Martin H Graham

Charles Matthew Corbalis

Charles H Jolissaint

James M Kasson

Howard W Johnson

Michael G Duncan

David Lieberman

Rod G Sinks

Michael D Jabara

An improved architecture for a computerized branch exchange particularly for a time division multiplexed bus used in the exchange. An intershelf bus includes a unidirectional source bus which receives signals from expanders and a unidirectional destination bus which transmits signals to the expanders. The expanders, through another bus, communicate with line cards which interface with telephone station sets, commercial lines, etc. A time division multiplexed controller updates distributed connection tables contained in each of the expanders and controls the flow of data onto and from the unidirectional buses. The distributed connection tables eliminate the need to broadcast addresses during each time slot. The arrangement is particularly useful in reducing blocking associated with prior art bidirectional buses.

Time division multiplexed computerized branch exchange

A distributed CBX system which provides a virtual network between remotely located CBXs is disclosed. The CBXs are connected to both a voice network and a packet network. A first CBX may interrogate a second CBX to determine, by way of example, the status of a called station at the second CBX over the packet network. The second CBX not only provides the status of the called station but also provides, if the called station is clear, the number of a free incoming line at the second CBX. In this manner, the first CBX can place a call to both an available line and station at the second CBX. Alternatively, because of facility availability or tariff structures, the call may be originated over common carrier facilities in the reverse direction originating over common carrier facilities from the called party end.

Distributed CBX system employing packet network

A dual tone multiple frequency digital tone generator for a PCM/TDM electronic telephone system. A digital representation of a dual tone signal is generated from a multi-bit command character by determining the phase angle of two frequencies specified by the command character relative to an independent time reference signal, converting paired phase angles to amplitude signals representative of the amplitude of a sine wave having each calculated phase angle, and summing the amplitude representations to generate a value corresponding to the digital representation of the frequency pair at that particular instant. Individual phase angles are calculated by generating a multi-bit digital character corresponding to the phase angle of a sinusoidal reference signal of the particular frequency. This character is preferably generated by multiplying a multi-bit digital character having n-bits representing the fractional part of the number of seconds elapsed from some reference time by a multi-bit digital character having m bits representing the frequency of the sinusoidal signal, m and n both integers. The resulting m + n bit product consisting of an m-bit integral part and an n-bit fractional part is examined and the p most significant bits to the right of the decimal point are selected, p being an integer. The value of n determines the accuracy of the product relative to the absolute value of the phase angle, while the value of p determines the resolution of the phase angle representation. Both n and p are preselected in accordance with the required accuracy of the frequency representation.

Method and apparatus for generating digital dual frequency signals

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Campbell, CA, United States of America

John D Edwards