# US 4,397,030 A · Digital communication system

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- Number: US 4,397,030 A
- Document ID: US4397030A
- Status: Granted
- Kind: A
- Application number: 06/244,368
- Filed: 1981-03-16
- Granted: 1983-08-02
- Earliest claimed: 1980-03-20
- Assignees: International Standard Electric Corporation
- Inventors: Dietrich Becker; Firoz Kaderali; Roland Liebscher
- Web page: https://patentgrep.com/patent/US4397030A

## CPC

- H04Q 11/0428: {Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals}
- H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W)

## Abstract

A digital subscriber terminal equipment is connected to the line circuit at a local exchange via a conventional subscriber line but permits simultaneous transmission of speech and data (e.g., viewdata). The terminal equipment and the line circuit each contain a central unit, a direction-separating unit, and a 10-bit data bus; the terminal equipment also includes a codec with a filter. The central units control the writing and reading of the digital signals into and out of the data bus and form on the subscriber line a main channel for data or speech, an additional channel for control, and an additional data channel.

## Claims

### Claim 1

A digital communications system comprising an exchange interconnecting a plurality of subscriber terminals, said exchange including a plurality of line circuits with each line circuit being connected to a separate one of said terminals over a bidirectional digital subscriber line, each line circuit and each terminal including a central unit, each terminal including a main source of digital data and certain of said terminals including an auxiliary source of data; a multiplex data bus in each terminal interconnecting said central unit, said main digital data source, the auxiliary data source with said bidirectional subscriber line; and means in said central unit of a terminal for directing digital data from each data word received from the line to said main source of digital data within the terminal for directing further data from each word to the auxiliary source within the terminal and for utilizing still further digital data from each word for signalling and for synchronizing said data bus.

### Claim 2 (depends on 1)

A digital communications system as claimed in claim 1, in which there is means in the central unit in each terminal for combining digital data from the main source with digital data from the auxiliary source and with signal data generated internally in said central unit into a data word for transmission over said data bus to said line.

### Claim 3 (depends on 2)

A digital communications system as claimed in claim 2, in which the central unit of each terminal includes digital transmitting means and digital receiving means, each including memory, encoding means and synchronizing means.

### Claim 4 (depends on 1)

A digital communications system as claimed in claim 1, in which each line circuit includes a bidirectional data bus for the transmission of digital data from a subscriber line to the central unit for further transmission and for the transmission of digital data from said central unit to a subscriber line.

### Claim 5 (depends on 4)

A digital communications system as claimed in claim 4, in which said line circuit central unit includes transmit means and receive means both for digital data and in which both said transmit and receive means comprise data memory, decoding means and a synchronizing circuit.