Optical communications network

• US 4,977,593 A
• Filed: 05/21/1990
• Issued: 12/11/1990
• Est. Priority Date: 11/27/1987
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Ballance, John W.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US07/488,048
• Time in Patent Office: 204 Days
• Field of Search: 455/612, 380/2, 380/48, 350/96.1
• US Class Current: 380/2
• CPC Class Codes: H04B 10/272 Star-type networks or tree-type networks
• CPC Class Codes: H04B 10/50 Transmitters
• CPC Class Codes: H04J 14/08 Time-division multiplex systems
• CPC Class Codes: H04J 3/0605 Special codes used as synchronising signal
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 25/03866 using scrambling

Abstract

A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g. telephones in customers'"'"' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibers at a first splitter (10) (e.g. array of passive couplers) and between further sets of fibers at a second set of splitters (12). At this stage there are 120 individual fibres to customers'"'"' premises (8). Digital speech or data is sent back to the central station by a laser in the customers'"'"' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Claims

1. A central station for a digital communications network comprising a plurality of outstations and a branch network of waveguides comprising a single waveguide from the central station, one or more passive splitters and two or more secondary waveguides for bidirectional transmission to and from the outstations:

the central station comprising transmitting means for transmitting data to outstations in the form of a stream of frames, each comprising a synchronisation signal in the form of a predetermined pattern of bits; and

characterised by scrambling means for scrambling the synchronisation signal and at least some of the data bits of each of the frames in accordance with a predetermined binary sequence; and

by means for detecting in data received from the outstations the presence of the scrambled synchronisation signal thereby obtaining information concerning reflections in the branch network.

2. A central station as claimed in claim 1 wherein each frame comprises a first portion comprising the synchronisation signal, and a second portion comprising traffic data, and wherein the scrambling means is arranged to scramble the first portion with said predetermined binary sequence, and to scramble the second portion with another predetermined binary sequence.

3. A central station as claimed in either claim 1 wherein the or each predetermined binary sequence is a pseudo random binary sequence.

4. A central station as claimed in claim 1 wherein said predetermined pattern is a sequence of zero bits.

5. A central station as claimed in claim 1 wherein the detecting means comprises an autocorrelator.

6. A digital communications network comprising a central station as claimed in claim 1, a plurality of outstations and a branch network of waveguides comprising a single waveguide from the central station, one or more passive splitters and two or more secondary waveguides for bidirectional transmission to and from the outstations.