Browse Prior Art Database

Station Line Interface Card

IP.com Disclosure Number: IPCOM000042942D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Kimberly, DW: AUTHOR [+4]

Abstract

This modular unit, attachable to a computer system, provides an interface between multiple conventional voice telephone subscriber sets and a switching (e.g., PABX) network controlled by the computer system. Each such "subscriber line interface card" (SLIC) unit serves up to eight telephone sets, and provides a transformerless hybrid-type voice circuit linkage, with regulated gain, from each set to the switching network. Via its attachment to the computer system each SLIC unit receives control and supervision, and is also accessible for diagnostic communications enabling the computer system to check continuity of any voice path extending through the switching network between two (or more) linkage circuits in one or more SLICs. A SLIC unit (Fig.

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Station Line Interface Card

This modular unit, attachable to a computer system, provides an interface between multiple conventional voice telephone subscriber sets and a switching (e.g., PABX) network controlled by the computer system. Each such "subscriber line interface card" (SLIC) unit serves up to eight telephone sets, and provides a transformerless hybrid-type voice circuit linkage, with regulated gain, from each set to the switching network. Via its attachment to the computer system each SLIC unit receives control and supervision, and is also accessible for diagnostic communications enabling the computer system to check continuity of any voice path extending through the switching network between two (or more) linkage circuits in one or more SLICs. A SLIC unit (Fig. 1) contains a multiplexing and control section 1 interfacing with the computer system I/O attachment bus, a ringing section 2 for supplying ringing current to attached subscriber sets, a loop current feed network 3 for supplying power to attached subscriber sets, a section 4 for providing transformerless hybrid linkages from subscriber sets (2-wire) to the switching network (4-wire) and a network of operational amplifiers 5 for providing transmission gain and signalling/testing capability. The ringing section, which has the function of selectively operating the electromechanical bell equipment on attached subscriber sets when instructed to do so by control section 1, is activated by a 100 VAC signal at a frequency of at least 20 Hz. Its circuits can be adapted to provide such "enhancement" functions as: zero voltage switching, staggered ring cycles, ring cycle timing, and ring tripping. The current feed network 3 contains suitable current sink and source components. It is designed to maintain a DC impedance of approximately 400 ohms and an AC impedance of approximately 900 ohms.

This circuit also monitors the on/off hook status of attached sets and can be instructed to remove power from any set. The hybrid linkage section 4 contains circuits for monitoring and controlling current devices in section 3, as well as circuits for providing the above-mentioned hybrid linkage paths. The operational amplifiers of amplification section 5 are inserted into the 4-wire transmission paths to provide gain for transmission and reception of voice signals. Biasing networks associated with these amplifiers limit transmission output levels and permit transmission of signals representative of binary (logical 1 and 0) information between SLICs.

This feature is useful for the continuity testing operation described below. These signals are detectable via high input impedance gates tied to the reception circuits. Fig. 2 illustrates schematically how two "local" subscribers A and B are interconnected (the procedure for local-remote connection is similar). Assume that subscriber A, whose set is attached to SLIC 20, calls subscriber B, associated with...