Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1992-05-29
1997-09-09
Chin, Wellington
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359117, H04J 1400
Patent
active
056662181
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to generalised connection networks of particular, but not exclusive, application to optical networks.
2. Related Art
Optical space switches can provide broadband switched connections in PBX and local network environments. Generalised connection networks (GCNs) offer the additional facility of broadcasting, for example, from any one of N inputs to any number up to N of outputs enabling any customer in a local network, for example to become a broadcast service provider to any combination of the other customers. The smallest GCNs published to date operate by separating the broadcast function into two parts; an initial replication network (generaliser) to generate the required number of copies, followed by a one-to-one switching network (connector) to connect the copies to the appropriate outputs. This segregated approach requires more crosspoint switches than the Nlog.sub.2 N theoretically needed to provide all of the N.sup.N possible permutations. GCNs using make/break contacts require 5.8Nlog.sub.2 N, and when using optical changeover switches they require in the order of 2Nlog.sub.2 N-N+2.
FIG. 2 of Sakata et al "Synthesis of Multiconnected Switching Networks, Electronics and Communications in Japan, vol, 58-A, no. 1, 51-58 (1975)", shows a GCN in which a branching network is positioned between a left-hand and a right-hand sub-network made up from two input, two output, 2-state branching elements whose task is either to allow both inputs through unaltered, or to copy one input, the upper input, to both outputs. In optics, where 2.times.2 changeover switches naturally perform a crossover function, their use as branching elements requires disconnection of the lower input line when copying, and this is easily provided by turning off the light source not seeking connection through the network or by adding a net of N additional on/off switches. A signal at a given input can be copied to a subset of outputs of the branching network as desired by passing sequentially through the switches in a downward direction. The right hand permutation network then interconnects the output of the branching network to the desired outputs of the GCN.
SUMMERY OF THE INVENTION
According to the present invention a generalised connection network comprises a first and a second interconnection sub-network interconnected by a branching network having N inputs and N outputs characterised in that the branching network has N, two-state branching elements interconnected so as to be able to replicate a signal coupled to any one of the N inputs to each of up to N outputs.
This is achieved by connecting N branching elements to provide a cyclic connection scheme (cylindrical symmetry) around the branching network which then permits any degree of branching, i.e. replication, of a signal on any one of the N inputs of the branching circuit because the branching elements form a complete cycle. This is in contrast to the previously mentioned Sakata et al arrangement which uses only N-1 branching elements which allows the i.sup.th input (where i=1 to N) to be replicated only (N-i) times.
The applicant has realised that the inclusion of the additional two state branching element in the branching network allows for a reduction by more than one two-state switch in the total number of two-state switches in the first and second Sub-networks thereby achieving a net gain in terms of two state switching elements needed to form a generalised connection network. In particular an 8.times.8 GCN according to the present invention requires a second sub-network having only 12 two state switches in contrast to the 17 needed for the Sakata GCN.
It will be understood that each two-state branching element may be made up one or more simultaneously operated switch elements depending, for example, on the technology and switch topology chosen.
Each branching element may have two branching element inputs and two branching element outputs and be switchable between a first state in which each br
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Bacares Rafael
British Telecommunications public limited company
Chin Wellington
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