GB2296159A - A communication switch - Google Patents

Abstract

A communication switch comprises a matrix of switch modules interconnected to allow switching between multiple inputs and multiple outputs, characterised in that said switch modules are distributed between multiple input/output port cards (CD) so that each card incorporates one or more switch modules (SW) with multiple outputs (T1-T4) connected to respective output ports (OUT) of the card and multiple inputs (N1-N8) connected to respective transfer terminals (TR1-TR8) of the card, the inputs (N1-N8) of the switch modules (SW) of all the cards (CD) being interconnected via a set of buses (B1-B8) connected to said transfer terminals (TR1-TR8), and a selector (SL) being incorporated in each card (CD) which is setable to connect each of one or more respective input ports (IN) of the card (CD) to a selected input (N1-N8) of said switch modules (SW) on the same card so that each input port (IN) of the switch is uniquely connected via a respective selector (SL) to a respective input (N1-N8) of a switch module (SW) and to a respective bus (B1-B8). <IMAGE>

Description

COMMUNICATION SWITCHES This invention relates to communication switches for use in communication systems to switch connections between respective input and output ports for the transfer of data therebetween.

A known type of communication switch, commonly called a "matrix switch", is used to connect any one of multiple input ports to any one of multiple output ports. Matrix switches can be used locally to interconnect local input and output ports, or centrally to inter-connect input and output ports of remotely located devices. For example, when port cards are interconnected in a communication system, a central matrix switch card is provided having the required level of connectivity for the total number of card input ports and card output ports. This creates a problem with expandable communication systems in that, even though the system may initially only incorporate a limited number of port card options, the same central matrix switch card with the maximum potential connectivity is still used. This makes the initial installation cost disproportionately high.

An object of the present invention is to provide a communication switch and system in which this problem is overcome or reduced.

This is achieved according to the invention by distributing the central matrix switch between the port cards so that the connectivity of the switch increases as additional port cards are added.

In particular, the invention consists in a communication switch comprising a set of switch input ports; a set of switch output ports; a set of switch transfer terminals; a set of matrix switch modules each having a set of inputs, a set of outputs and a set of interconnection terminals; and a selector; the switch modules of said set having their outputs connected in series by interconnections between the respective outputs and interconnection terminals of successive switch modules with the outputs of the last switch module in series being connected to the switch output ports, each of the inputs of the switch modules being connected to a respective switch transfer terminal so that a signal at any transfer terminal can be switched to any output port, and the selector being set to further connect the input ports to the inputs of one of said switch modules so that a signal at any input port can be switched to any output port.

A communication system according to the invention comprises two or more of the aforesaid communication switches, each being connected to a set of buses via said transfer terminals so that each input port is uniquely connected via its respective selector to an input of a switch module on the same card and to a corresponding bus. The total number of input ports of all the communication switches therefore equals the total number of buses employed to give a non-blocking communication system. It is preferred that each switch module comprises a square matrix switch with the same number of inputs, outputs and interconnection terminals.

A communication switch according to the invention may comprise just one set of matrix switch modules connected in series with just one set of output ports, and a corresponding set of input ports. However, the switching capacity of a communication switch can be increased by providing multiple sets of switch modules, each set being connected in series with a corresponding set of output ports, and the inputs of these multiple sets of switch modules being connected in parallel with the transfer ports so that a signal at any transfer terminal can be switched to any one of the output ports.The multiple sets of output ports are then matched by multiple sets of input ports, equal in number to the sets of output ports, with each set of input ports being connected via the selector to the corresponding transfer terminals, thereby to the inputs of the corresponding switch module in each set of switch modules. An appropriate number of buses are then provided to interconnect the multiple sets of input ports and multiple sets of output ports with other communication switches in a non-blocking communication system.

Thus each switch module may have different numbers of input ports and output ports.

The number of switch modules incorporated in each set of switch modules in a communication switch will be equal to the number of sets of switch modules used in the system.

According to another feature of the invention, the communication switches are incorporated in units that are stacked one on top of another vertically, with electrical interconnections provided between their cooperating surfaces.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic drawing of a communication system according to a first embodiment of the invention; Figure 2 is a schematic drawing of the mounting arrangement of the output cards in the system of Figure 1; Figure 3 is a schematic drawing of a communication system according to a second embodiment of the invention; and Figure 4 is a schematic drawing showing a modification to the communication system of Figures 1 or 3.

The illustrated communication system carries information in an ATM cell format and comprises two communication switch cards CD1 and CD2, each with four input ports IN1 to IN4 and IN5 to IN8, respectively, and four output ports OUT1 to OUT4 and OUT5 to OUT8, respectively. These two cards are interconnected via a backplane B having eight buses B1 to B8 to which each card is connected via eight transfer terminals TR1 to TR8.

Each card CD1 and CD2 incorporates two matrix switch modules SW1.1 and SW1.2 and SW2.1 and SW2.2, respectively, each of these modules SW being a square matrix switch having four inputs N1 to N4 or N5 to N8 and four outputs T1 to T4 or T5 to T8. The two modules SW on each cards have their outputs connected in series by interconnections between the outputs T5 to T8 of one module SW1.2 or SW2.2 and interconnection terminals R1 to R4 of the other module SW1.1 or SW2.1 so that each pair of modules forms a combined matrix switch with eight inputs N1 to N8 and four outputs T1 to T4.Input signals on any one of the inputs N1 to N8 can then be switched to any one of the outputs T1 to T4 according to routing information incorporated in the routing tags of the ATM cells as further described below.

The four outputs T1 to T4 of the second series connected module SWl.l or SW2.1 are connected via four respective line transmitters LT1 to LT4 or LT5 to LT8 to the four output ports OUT1 to OUT4 or OUT5 to OUT8 of the respective card. The eight inputs N1 to N8 of each pair of modules SWl.l, SW1.2 and SW2.1, SW2.2 are each connected to a respective one of the buses B1 to B2 via a connector P1 or P2 comprising eight transfer terminals TR1 to TR8 on the card CD1 or CD2. The four input ports IN1 to IN4 or IN5 to IN8 are connected via four respective line receivers LR1 to LR4 or LR5 to LR8 and a selector SL1 or SL2 to the four inputs N1 to N4 or N5 to N8 of one of the modules SW as determined by the setting of the selector SL1, SL2 so that the four inputs IN1 to IN4 of one card CD1 are connected to the inputs N1 to N4 of the second module SW1.1 in series on that card, and the four inputs IN5 to IN8 of the other card CD2 are connected to the inputs N5 to N8 of the first module SW2.2 in series on that card.Each set of four input ports IN1 to IN4 or IN5 to IN8 is therefore also connected via the connector P1 or P2 to a respective set of buses B1 to B4 or B5 to B8 in the backplane B.

In the operation of the system, any data received at an input port IN1 to IN8 is processed by the respective line receiver LR1 to LR8 which generates the routing tag by which this data is to be routed through the system to the corresponding output port OUT1 to OUT8. The input data is then transmitted via the selector SL1 or SL2 to that input N1 to N8 of the modules SWl.l, SW1.2 and SW2.1, SW2.2 to which that particular input port IN1 to IN8 is connected. The input data is also transmitted to the corresponding bus B1 to B8 to which this input N1 to N8 is connected.For example, a data input at input port IN1 is applied via the selector SL1 to the input N1 of the module SW1.1 and to the bus B1.

Each of the switch modules SW operates to analyze the ATM cells applied to its inputs N1 to N4 or N5 to N8 and reads the routing tag of every ATM cell to determine whether that cell is intended for one of the output ports OUT1 to OUT4 or OUT5 to OUT8 to which the module is connected. If this condition applies, then the cell is transmitted by the module SW to the appropriate output port OUT1 to OUT8 via a respective line transmitter LT1 to LT8 which removes the routing tag.Thus, if data is to be transmitted between the input ports and output ports of the same card CD1 or CD2, then the route switching occurs in a switch module SW of that same card, but if the data is to be transmitted between the input port of one card CD1 or CD2 and an output port of the other card CD2 or CD1, then the route switching occurs in a switch module SW of that other card after transmission of the data on the corresponding bus B1 to B8 connecting said input port to the switch module of said other card.

The routing tag employed may, for example, comprise a plurality of subfields, each corresponding to a particular card CD1 or CD2 in the system, and each comprising a code that identifies one or more of the possible four output ports OUT1 to OUT4 or OUT5 to OUT8. It will be appreciated that a cell can be transmitted to any or all of the output ports OUT1 to OUT8 by the use of appropriate output codes.

An example of a suitable matrix switch module SW for use in the illustrated embodiment of the invention is the Fujitsu MB86680B ATM Switch Element.

A conventional physical arrangement of the cards CD1, CD2 of a system would involve mounting the cards upright in a rack with the connectors P1, P2 at the rear edge between the cards and an upright motherboard that incorporates the backplane. An alternative arrangement, however, is illustrated in Figure 2 in which the cards CD1, CD2 are stacked one on top of another. The bottom card CD1 is the first, and in some systems may be the only card that is required, and thus it is supplied in a housing unit H with other system requirements, such as a power supply PSU, a management control card CDM and a fan tray FT. The other cards CD2, CD3 etc. do not include the management control card CDM or power supply unit PSU, -but each is mounted in a housing unit H and is provided with a fan tray FT.The connectors P1, P2 between cards CD1, CD2, CD3, etc, are provided as cooperating two part connectors that engage automatically as the cards are stacked.

The buses B1 to B8 may, for example, each comprise a multiconductor parallel bus having eight conductors carrying data, one carrying a synchronisation signal, and one carrying a clock signal.

The setting of the selectors SL1, SL2 to make the appropriate unique connections between the input ports IN1 to IN4 and IN5 to IN8 can be predetermined by the connectors P1, P2, the engagement of a connector when plugging in a card CD1, CD2 to a socket in the backplane B serving to set the selector SL1, SL2 in the appropriate manner. Alternatively, the system may include a control unit which identifies those connectors P1, P2 that have been made and those that have not been made, and sets the selectors SL1, SL2 accordingly.

It will be appreciated that the illustrated system can be readily expanded to incorporate three or more cards by increasing the number of buses in the backplane B so as to accommodate the extra interconnections required between cards for the extra input ports and output ports. At the same time, the number of matrix switch modules SW connected in series on each card will have to be increased so that the combined matrix switch still has a separate input for every bus. Thus, the addition of a third card in the illustrated system would require each card to have a third switch module with four inputs for the four extra buses and with the four outputs connected in series to the interconnection terminals R5 to R8 of the second modules SW1.2 and SW2.2 as shown in broken outline in Figure 1.Thus, in this example, the number of modules on each card equals the number of cards in the system, and the total number of modules equals the square of the number of cards.

An alternative embodiment of the invention is illustrated in Figure 3 comprising two communication switch cards CD1 and CD2, one of which CD1 incorporates a set of three matrix switch modules SWl.l, SW1.2, SW1.3 connected in series with a set of output ports OUT1 to OUT4 in the manner of the card CD1 illustrated in Figure 1, and the other of which CD2 incorporates two sets of three matrix switch modules SW2.2, SW2.2, SW2.3 and SW2.4, SW2.5, SW2.6 each connected in series with a set of output ports OUT5 to OUT8 and OUT9 to OUT12 in the manner of the set of switch modules SWl.l, SW1.2, SW1.3 of card CD1. As shown in Figure 3, each set of output ports OUT1 to OUT4, OUT5 to OUT8 and OUT9 to OUT12 are shown as a broad line for reasons of simplicity in the drawing, and it will be appreciated that each such broad line represents a set of four connections, ports or terminals.

Thus, the card CD1 has four input ports IN1 to IN4 connected via the selector SL1 to four inputs of the third switch module SWl.l, and each switch module SWl.l, SW1.2, SW1.3 has a set of four inputs connected via respective sets of transfer terminals TR1 to TR4, TR5 to TR8, TR9 to TR12 to respective sets of buses B1 to B4, B5 to B8, B9 to B12.

The card CD2 has two sets of four input ports IN5 to IN8 and IN9 to IN12, each connected via a selector SL2 to the inputs IN5 to IN8 of the second switch module SW2.2 and inputs IN9 to IN12 of the first switch module SW2.3, respectively.Also, each set of four inputs of each switch module SW2.1, SW2.2, SW2.3 is connected via respective sets of transfer terminals TR1 to TR4, TR5 to TR8, TR9 to TR12 to respective buses B1 to B4, B5 to B8, B9 to B12. Furthermore, each set of four inputs of the second set of switch modules SW2.4, SW2.5, SW2.6 is connected in parallel with the corresponding inputs of the respective switch modules SW2.1, SW2.2, SW2.3 of the first set, this being achieved using a set of four regeneration outputs RG1 to RG4, RG5 to RG8, RG9 to RG12 of the switch modules of the first set.Thus, card CD2 has eight input ports IN5 to IN12 and eight output ports OUT5 to OUT12 compared with the four input ports IN1 to IN4 and output ports OUT1 to OUT4 of the card CD1.

The communication switch cards CD1, CD2 of either Figure 1 or Figure 3 can be modified as shown in Figure 4 so that two or more input signals are multiplexed at each input port and demultiplexed into separate output signals at each output port, thereby effectively increasing the number of input and output ports within the maximum bit rate limit of each input port and output port. As shown in Figure 4, each input port IN1 to IN4 and output port OUT1 to OUT4 is divided into a pair of ports, which are combined with a multiplexer MX1 to MX4 at the inputs or demultiplexed by DX1 to DX4 at the outputs.

Claims (8)

CLAIMS:

1. A communication switch comprising a matrix of switch modules interconnected to allow switching between multiple inputs and multiple outputs, characterised in that said switch modules are distributed between multiple input/output port cards so that each card incorporates one or more switch modules with multiple outputs connected to respective output ports of the card and multiple inputs connected to respective transfer terminals of the card, the inputs of the switch modules of all the cards being interconnected via a set of buses connected to said transfer terminals, and a selector being incorporated in each card which is setable to connect each of one or more respective input ports of the card to a selected input of said switch modules on the same card so that each input port of the switch is uniquely connected via a respective selector to a respective input of a switch module and to a respective bus.

2. A communication switch according to claim 1 further characterised in that one or more cards each incorporate a set of two or more switch modules with the outputs of respective modules connected in series with the output ports.

3. A communication switch as claimed in claim 2 further characterised in that one or more cards each incorporate multiple sets of two or more switch modules associated with them, each set being connected in series with a corresponding set of output ports, and the inputs of these multiple sets of switch modules being connected in parallel with the transfer terminals so that a signal at any transfer terminal can be switched to any one of the output ports.

4. A communication switch as claimed in claim 2 or 3 further characterised in that each switch module of each set comprises a square matrix switch with the same number of inputs and outputs.

5. A communication switch as claimed in any one of claims 2 or 4 further characterised in that the number of switch modules incorporated in each set of switch modules is equal to the number of sets of switch modules used in the switch.

6. A communication switch as claimed in any one of the preceding claims further characterised in that the total number of input ports of the switch equals the total number of buses to give a non-blocking communication switch.

7. A communication switch as claimed in any one of the preceding claims further characterised in that the input/output port cards are incorporated in units that are stacked one on top of another vertically, with electrical interconnections provided between the cooperating surfaces of the units.

8. A communication switch as claimed in any one of the preceding claims further characterised in that one or more of the cards each has one or more multiplexers connected to the input ports to multiplex input signals before supplying them to the selector, and one or more de-multiplexers connected to the output ports to de-multiplex output signals from the switch modules before supplying them to the output ports.