Abstract: The digital tie line provides a high speed pulse code modulation (PCM) digital path between private branch exchange (PBX) systems. The invention has a capability of providing a plurality of simultaneous two-way channels. By providing for twice the number of available channels in each PBX system, PBX systems may be interconnected by using one digital tie line per system, resulting in a non-blocking traffic situation between systems. High speed digital data may be directly passed via assigned channels between systems. The digital tie line provides a connection between the internal system parallel PCM bus and an externally located serial bus. A multiple PBX network can be interconnected by multiple external buses by employing a single digital tie line in each PBX system, per external bus. A modular time slot interchanger (MTSI) is used to direct signals between the system PCM bus and the external bus.

Abstract: The disclosed digital conference circuit additively combines conference signals with a single adder, a partial sum accumulator RAM, and conversion ROMs. Internal conferencing time slots are dynamically assignable via a microprocessor controlled channel indexing memory. The signal level on lines can be selectively adjusted to compensate for loop attenuation on a per-line basis. The circuit can operate with a number of voice coding law PCM signals from CODECs by the use of conversion ROMs containing conversion tables for the selected voice coding law. Additive background noise levels may be reduced by the dynamic selection of modified sections of the conversion tables. The number of conferences available and the number of lines per conference is limited only by the number N of internal conferencing PCM time slots. The number of internal conferencing time slots used per conference equals the square of the number of lines in the conference.

Abstract: A ringing control system which receives ring inputs, detects the type of input, translates the input into digital PCM format for transmission across a digital line such as a multiple channel span line. At the remote end of the line, the PCM signals are reconverted into relay operating data for emitting output signals of types corresponding to the input ringing signals. The ringing signals may be divided ring for either the tip lead or the ring lead and also may be frequency selective, superimposed or coded ringing. The arrangement is designed for use in a digital multiplexer or subscriber loop multiplexer.