Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1997-09-16
1999-10-05
Chan, Jason
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359114, 359124, 359118, H04B 1024, H04B 1020, H04J 1402
Patent
active
059633484
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the assignment of wavelength channels to nodes in an optical bus network
BACKGROUND
In the sphere of telecommunications there is, in many cases, a need for a very high transmission capacity. Very fast data transmission can be achieved by using optical transmission by way of modulated light signals.
In order to send a plurality of light signals over a common optical medium, wavelength division multiplexing (WDM) is used. The signals are sent by way of independent wavelength channels, which can exist simultaneously in one optical fibre.
The optical transmission can be achieved in optical bus networks which comprise a number of optically connected nodes adapted for reciprocal communication. In an optical bus network comprising N nodes connected in series to one another, communication between nodes can be achieved in both directions by using at least two fibres for this communication, at least one fibre of which is used for each signal distribution direction. Each node communicates with each other node by way of a unique wavelength channel. This means that at least N-1 wavelength channels will exist simultaneously on each optical fibre.
A network which facilitates continuous communication between all nodes even following a fibre fracture between two nodes is already known from U.S. Pat. No. 5,159,595. The network comprises a number of nodes which are connected to one another in an circular configuration. This configuration is suited, for example, to wavelength division multiplexing.
When interruption occurs between two nodes, the wavelength channels which are used for communication to or from the said two nodes must change direction. The number of channels on the signal path used after interruption must then be increased In the known network additional channel assignment is facilitated in that each node comprises one transmitter port and one receiver port respectively, by means of which arbitrary wavelength channels can be added to or removed from the bus network. This solution, however, is both technically and economically disadvantageous.
SUMMARY
The method according to the invention relates to channel assignment in an optical bus network comprising N nodes connected in series to one another by way of two fibres. Each node communicates with each other node by way of a trasmitter and a receiver, so that each node comprises N-1 transmitters and N-1 receivers. Each transmitter in the network transmits a certain wavelength channel. Each receiver in the network receives a certain wavelength channel and allows other wavelength channels to pass on to the next node. The channel which is received by a receiver in a node is removed entirely from the network, whereafter the channel can be reused for transmission of information between two other nodes. In this way a minimum number of channels can be used for this communication between the nodes.
In order to avoid a fibre fracture in the bus network preventing all communication between certain nodes, an additional, geographically separated, pair of fibres is provided, which connect the first and last node of the bus network. This pair of fibres is activated if any of the ordinary fibres is damaged, the arrangement being designed to completely prevent communication past the point of interruption by way of the ordinary fibres. The network then acquires another configuration in such a way that the arrangement between the nodes must be changed and transmitter and receiver switched over.
One problem with previously known methods of channel assignment in optical bus networks is that an interruption of the above-mentioned type in the network generally leads to channels having to be re-assigned to each node, since channel collisions otherwise occur when the network configuration is changed.
The invention is intended to solve the above-mentioned problem in that it provides a new method for channel assignment in an optical bus network, by means of which a minimum number of channels is assigned to a node, in such a way tat the cha
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Forghieri, Fabrizio et al., "Reduction of Four-Wave Mixing Crosstalk in WDM Systems Using Unequally Spaced Channels," IEEE Photonics Technology Letters, vol. 6, No. 6, pp. 754-756, Jun. 1994.
Ghose, Kanad, "Performance Potentials of an Optical Fiber Bus Using Wavelength Division Multiplexing," SPIE, vol. 1849, Optical Interconnects, pp. 172-183, 1993.
Chan Jason
Sedighian Mohammad
Telefonaktiebolaget LM Ericsson
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