GB2189104A

GB2189104A - Optical switching network

Info

Publication number: GB2189104A
Application number: GB08608174A
Authority: GB
Inventors: Martin Philip Owen; Terence Paul Young
Original assignee: General Electric Company PLC
Current assignee: General Electric Company PLC
Priority date: 1986-04-03
Filing date: 1986-04-03
Publication date: 1987-10-14
Anticipated expiration: 2006-04-03
Also published as: GB2189104B; GB8608174D0

Abstract

An optical communications switching network comprises a plurality of two-by-two switching elements 1-8, provided in a configuration in which every path from an input to the system at some point crosses every other path whereby to render the system "intelligently non-blocking", whilst not necessarily strictly non-blocking. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Switching Networks This invention relates to switching networks and in particular to switching networks for use in optical communications systems.

With the increasing use of optical communications, the need has arisen for relatively large optical switching networks based upon a "two-into-two" element. In this, a pair of incoming signals or calls either go straight through (the "through" state) or cross over in the switching element, as illustrated in Figure 1 of the accompanying drawings.

In any communications switching network it is obviously desirable to reduce the number of switching elements involved and the desire for a minimum number of elements in the network has recently been further stimulated by the inherent limitations of optical switches in terms of fabrication, cross-talk and loss.

In conventional switching networks the conventional approach is to link small networks (nxm using n.m elements) into larger networks.

This results in overall switching element savings for numerically large n and m networks. However, the penalties associated with using n2 elements for nx n optical switches (even for low numerical values of n, i.e. < 32) means that there are real advantages to be gained in providing networks which fall below then2 limit.

In any design which falls below the n2 limit, the question of "blocking" is of paramount importance and "non-blocking" networks are generally required. A non-blocking switching network is one in which a newly incoming signal or call can be routed through the network without interfering with the established remainder of the network. For networks in which every input is connected to one of the outputs at all times (i.e. the n2 case), the nonblocking criterion reduces to the statement that any call route through the network may be swapped with any other without disturbing the remainder of the network.

As at present common, a non-blocking network may be considered to fall into one of two categories, i.e. strict non-blocking and rearrangeable nonblocking. With the strict non-blocking case, nonblocking is guaranteed by the network structure provided, of course, this remains good.

Rearrangeable non-blocking networks on the other hand take into account the possibility of breakages within the network and aliow for rearrangement of the network in the face of blockages to provide a non-blocking configuration. The strict non-blocking case referred to above is not economical in terms of switching elements since for n signals, n2 elements are required when n is equal to or less than 32 and a number proportional to n3/2 is required above that numerical value for n. The last-mentioned may be acceptable for telephone exchanges, but not necessarily if the network is to be suitable for use with a computer data communications system.

The present invention seeks to provide an improved communications switching network, and in particular an improved optical communications switching network using a number of switching elements which is less than the number conventionaliy required for strict non-blocking.

According to this invention a switching network and in particular an optical communications switching network is provided which, whilst not strictly non-blocking, is prevented from blocking by intelligent use of switching. Normally said intelligent use will be under control of a computer or microprocessor.

According to a feature of this invention a switching network comprising a plurality of switching elements, and in particular so-called twoby-two switching elements are provided in a configuration in which every path from an input to the system at some point crosses every other path.

In essence the system provided by the present invention may be regarded as "intelligently nonblocking".

One example of an optical switching network in accordance with the present invention will now be described with reference to Figure 2 of the accompanying drawings.

Referring to Figure 2 in which the switching network is represented schematically, four optical signal inputs are considered (i.e. n=4). In Figure 2 the inputs are referenced A, B, C and D. An array of eight individual optical switching elements are arranged in a matrix. Each individual switching element is a "two-by-two" switching element.

Element 1 receives as input optical signals A and B whilst optical element 2 receives as input optical signals C and D. The two outputs of optical element 1 are connected one to one input of switching element 3 and the other to one input of switching element 4. Similarly one output of switching element 2 is connected to the other input of switching element 3 and the other output of switching element 2 is connected to the other input of switching element 4.

In turn, one output of switching element 3 is connected to one input of switching element 5 whilst the other output of switching element 3 is connected to one input of switching element 5.

Similarly one output of switching element 4 is connected to the other input of switching element 5 whilst the other output of switching element 4 is connected to the other input of switching element 6.

In turn, one output of switching element 5 is connected to one input of switching element 7 whilst the other output of switching element 5 is connected to one input of switching element 8.

Similarly one output of switching element 6 is connected to the other input of switching element 7 whilst the other output of switching element 6 is connected to the other input of switching element 8.

The four outputs provided by the switching elements 7 and 8 are referenced E, F, G and H but it will be appreciated that appearing at E, F, G and H may be any of input signals A, B, C and D depending upon the manner in which the individual switching elements 1 to 8 are set to a "through state" or a "cross state" as already described with reference to Figure 1.

As will be appreciated, with the network illustrated in Figure 2, for n=4, the saving in individual switching elements compared to a n2 strict non-blocking system is 50%.

Claims

1. A communications switching network which, whilst not strictly non-blocking, is prevented from blocking by intelligent use of switching.

2. A communications switching network comprising a plurality of switching elements provided in a configuration in which every path from an input to the system at some point crosses every other path.

3. A network as claimed in claim 2 and wherein said switching elements are so-called two-by-two switching elements.

4. An optical communications switching network as claimed in any of the above claims.

5. A communications switching network as claimed in any of the above claims and wherein said intelligent use is under the control of a computer or microprocessor.

6. A communications switching network substantially as herein described with reference to Figure 2 of the accompanying drawings.

6. An optical communications switching network substantially as herein described with reference to Figure 2 ofthe accompanying drawings.

Amendments to the claims have been filed, and have the following effect: (a) Claims 2 to 6 above have been deleted or textually amended.

2. A communications switching network as claimed in claim 1 comprising a plurality of switching elements provided in a configuration in which every path from an input to the system at some point crosses every other path.

3. A communications switching network as claimed in claim 2 and wherein said switching elements are so-called two-by-two switching elements.

4. A communications switching network as claimed in any of the above claims wherein said network is an optical communications switching network.

5. A communications switching network as claimed in any of the above claims and wherein said intelligent use is underthe control of a computer or microprocessor.