Multiplex communications – Wide area network – Packet switching
Patent
1987-07-27
1990-09-04
Orsino, Joseph A.
Multiplex communications
Wide area network
Packet switching
342 15, 455607, 455600, H04B 900
Patent
active
049550136
DESCRIPTION:
BRIEF SUMMARY
A multiple-access optical network has a plurality of communication stations, the stations being physically coupled together by optical waveguides (usually optical fibres) and arranged such that ecah station can transmit signals to one or more of the other stations. Such communication networks are referred to as multiple-access (MA) networks since any station can receive signals from a number of the other stations.
Recently proposed multiple-access networks have been based on optical fibre links which offer a relatively secure, closed, transmission medium. However, one of the most attractive signal distribution schemes from a network insertion loss and reliability point of view, i.e. the transmission-star coupler, has a disadvantage of distributing information transmitted from one station to a number of the other stations. This information could be protected using data encryption techniques but this is costly.
In accordance with the present invention, a method of operating a multiple-access optical network having a plurality of communication stations, the stations being physically coupled together by optical waveguides and arranged such that each station can transmit signals to one or more of the other stations but cannot receive signals it has itself transmitted, comprises causing one station to transmit information over a selected channel to a receiving station an causing the receiving station to transmit simultaneously a signal over the same channel.
This invention finds use, for example, in the type of passive multiple-access network which is described in more detail in published GB patent application No. 2172165A, "Optical Signal Power Divider", of Faulkner and Healy, published on Sept. 10, 1986 and issuing on Mar. 1, 1989, in the name of British Telecommunications plc. The power dividing network described in that patent application sets out to reduce the number of communications channels required in a passive network by using a topology in which a transmitting station is unable to receive its own transmitted signal.
The present invention aims to provide a method of operating networks with passive network topologies in which a transmitting station cannot receive its own transmitted signal to provide a natural degree of data security.
In some cases, both stations may transmit information to each other over the same channel.
Thus, the method according to the present invention of causing one station to transmit information over a selected channel to a receiving station and causing the receiving station to transmit simultaneously a signal over the same channel, may comprise operating the network in full-duplex operation over a single transmission channel.
In this case, stations not associated with the two communication stations will receive both transmissions simultaneously and it will be very difficult for those stations to decipher the two simultaneous signals in such a busy channel, giving a degree of natural data security. The two communication stations, on the other hand, can use the same transmission channel without causing mutual interference.
In other cases, the method comprises causing the station which is to receive information to transmit an interfering signal in the same channel as the information transmitted by the other station, the interfering signal being received at each of the other stations which also receives the information.
This second arrangement provides a more secure transmission system than in the first cases mentioned above allowing each receiving station to protect its own incoming information by effectively blocking all other stations from receiving information in that channel.
Conveniently, the station transmitting information may monitor its own receiving channel to confirm that the interfering signal is present before information is transmitted.
The channels may be based on any multiple-accessing technique such as wavelength, frequency, time, or code division.
The physical connections between stations may be provided by optical fibres, typically monomode optical fibres.
The
REFERENCES:
patent: 3718765 (1973-02-01), Halaby
patent: 4317214 (1982-02-01), Attinello
patent: 4530084 (1985-06-01), Strebel et al.
"Designing with Low Cost Fibre Optic Links" by D. Knight, Electronic Engineering, vol. 55, No. 674, Feb. 1983, pp. 39-53, London, GB.
JP-A-58 204 645, Patent Abstracts of Japan, vol. 8, No. 49, (E-230) [1486], Mar. 6th, 1984, (Tokyo Shibaura Denki K.K.), 29-11, 1983.
"Optical Cascade Star Network--A New Configuration for Passive Districution System with Optical Collison Detection Capability" by Tamura et al., J. Lightwave Technology, vol. LT-2, No. 1, Feb. 1984, pp. 61-66.
"New Transmissive Star Couplers for Full Duplex Channels" by Healey et al., IOOC-ECOC, 1985, pp. 589-592.
Beek L. Van
British Telecommunications PLC
Orsino Joseph A.
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