Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1997-11-20
2000-04-11
Pascal, Leslie
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359125, 359110, 359161, H04B 1020
Patent
active
060494050
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL BACKGROUND
The present invention concerns an optical node in an optical bus network. The node comprises transmitters and receivers which are adapted to particular wavelength channels and are arranged to communicate via the optical bus network with receivers and transmitters for corresponding wavelength channels in other nodes.
The invention also concerns a process carried out in an optical bus network.
PRIOR ART
Within the field of telecommunications, there is frequently a need for high transmission capacity. Large amounts of data can be transmitted very rapidly by using optical transmission via modulated light signals.
Wavelength multiplexing (WDM) is used to transmit a plurality of light signals via a common optical medium. The signals are sent via independent wavelength channels which can be present simultaneously in an optical fibre.
Optical transmission can be brought about in an optical bus network which comprises a plurality of optically connected nodes adapted for mutual communication. In the case of an optical bus network having N nodes connected in series with one another via two optical fibres, communication in both directions between the nodes can be brought about as a result of the first fibre being used for transmission in one direction and the second fibre being used for transmission in the other direction. Each node communicates with each other node via a single wavelength channel. This means that at least N-1 wavelength channels are present at the same time on each optical fibre.
Each node comprises at least N-1 receivers and N-1 transmitters which communicate via wavelength channels with transmitters and receivers corresponding to these channels in the other nodes. Each transmitter transmits information which is input on one of the two optical fibres; each receiver receives information which is tapped from one of the two optical fibres.
The optical bus network is preferably arranged so that, in the event of an interruption in the network, communication between all of the nodes can be maintained by a pair of reserve fibres intended for interruption situations. However this type of interruption actuates the communication between the different nodes and involves one or more receivers and transmitters in each node having to change such that it receives or sends, respectively, a wavelength channel via some of these reserve fibres. In order to restrict the number of wavelength channels used, it is possible to re-use channels. Re-using channels means that one or more wavelength channels received in a node are used for transmission from the same node on the same fibre when this is possible. The smallest number of channels which can be used is restricted by the number of nodes to N.sup.2 /4 if N is even or (N.sup.2 -1)/4 if N is odd. Since the same channel is consequently used many times for transmitting on the same fibre, problems can arise when communication between two nodes is also to be maintained when there has been an interruption in the network.
U.S. Pat. No. 5,159,595 has already disclosed a network comprising a number of nodes which are connected to one another in an annular configuration. Each node can communicate with each other node via the network. In the case of a conventional network configuration, each message is transmitted between two nodes via both fibres from a dispatching node to a destination node; in the same way a message from both oppositely directed fibres is received in a node. This means that communication in the case of an interruption in the bus network can be maintained without switching being necessary. A disadvantage with this system is that the network normally has an unnecessarily large amount of wavelength channels and is therefore over-dimensioned.
DESCRIPTION OF THE INVENTION
The invention concerns an optical node which is adapted for communicating, via transmitters and receivers connected to two optical fibres, with at least two other optical nodes in an optical bus network. This bus network comprises extra communication paths for ensuring t
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Pascal Leslie
Phan Hanh
Telefonaktiebolaget LM Ericsson
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