GB2251158A

GB2251158A - Improved signal switching arrangement

Info

Publication number: GB2251158A
Application number: GB9121812A
Authority: GB
Inventors: James Campbell Kidd
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-11-24
Filing date: 1991-10-15
Publication date: 1992-06-24
Anticipated expiration: 2011-10-15
Also published as: GB9121812D0; GB9025600D0; GB2251158B

Abstract

An improved signal switching arrangement, primarily for use in a multiprocessor computer, wherein nodes of the system such as processing elements are located on separate processing modules 20 and a signal path between two or more nodes of the system is created via a network of switching elements located both on the processing modules and on separate switching modules 30. The processing and switching modules are arranged such that edges of the processing and switching modules intersect and electrical connections 11 are placed at those intersections. Additionally, management and control signals are provided to each element of the system and power supply to each element of the system is via individual power supply units located on each module. <IMAGE>

Description

Improved Signal Switching Arrangement This invention relates to large scale signal switching arrangements and, more particularly to a signal switching arrangement within a multiprocessor computer.

In any signal switching arrangement, two or more nodes of the system are connected via a signal path. The signal path may support optical signals, or analogue or digital electrical signals, and may include other features such as signal buffering, retiming, or routing based on packet headers. At present, many such arrangements are known, however, the disadvantages of the present arrangements may be seen more clearly by referring to an example, such as a multiprocessor computer system.

Compared with conventional, single processor, computers, improved performance may be achieved by distributing the processing load between two or more processing elements. In order that the processing elements may communicate with one another, a signal switching array is often employed which, normally, is capable of creating a signal path between one processing element and any other processing element.

The power of a multiprocessor computer may be increased by adding more processing elements. However, if there are N processing elements, there will be Nx(N-l) possible paths between them. Therefore, as more processing elements are added, the complexity of the signal switching arrangement is increased greatly.

Consequently, the useful power of a multiprocessor computer is often limited by the size of the signal switching arrangement.

Currently, there are available many types of integrated circuit that contain electronic switching elements. For example, the CD74HCT22106E manufactured by Harris Semiconductor includes an 8 x 8 analogue crosspoint switch and the Inmos IMSC004 includes a 32 x 32 uni-directional digital crossbar switch together with signal buffering and retiming.

An advantage of crossbar switches over other types of switch is that they allow all output ports to be connected simultaneously (and in any order) to the input ports. It may be noted also that the signal bandwidth through the switch matches the bandwidth both into and out of the switch. These crossbar switches maybe of any size. An example with 32 inputs and 32 outputs is commonly known as a 32 x 32 crossbar. In the literature on networks, 2 x 2 crossbars are often used. These are easy to draw, have only 2 states (straight-through and crossover) and can easily be physically realised with electro-mechanical relays.

Usually, there exists a one-to-one relationship between the input and output ports. It is sometimes possible to connect one input to several outputs. However, this is an extension to the basic principle and is not considered here.

Physical constraints, such as the maximum number of pins that are practical on a package, limit the size of single-chip switching elements.

Fortunately, larger switches can usually be made from arrays of smaller switching elements. There are numerous ways of connecting crossbar switch elements together to form larger crossbar arrays. However, Butterfly networks may be considered to be the best general solution. For crossbar switches with large numbers of ports, they use the smallest number of switch elements whilst still retaining the properties of simultaneous connection and bandwidth preservation as described above. One such array, commonly known as a 3-rank Butterfly network, may be constructed from forty-eight individual 32x32 crossbar switching elements, arranged into three ranks, each of sixteen elements. Using currently available integrated circuits, such as Inmos IMSC004s, in the place of each switching element provides a network capable of supporting up to 1024 nodes.Similarly, a 3-rank Butterfly network may be extended further; for example a 5-rank Butterfly network may support up to 32768 nodes.

The wiring of such large networks presents further problems. As can be seen above, there will be a multitude of connections between the many switching elements. Also, in switching arrangements such as Butterfly networks, where connections run from each element of one rank to every element of the next rank, a nest of connections is created which is difficult to implement using current printed circuit board techniques.

Often, users of such machines initially wish to purchase a sub-maximal system and then later upgrade it when they are more confident in the machine or more certain of their requirements. It is therefore desirable that any such system should support a wide range of configurations and that the manufacturing costs should be concentrated as much as possible in the elements that may be used -to upgrade the system.

A traditional method of creating a multiprocessor computer is to connect several processing elements by one high performance bus. The system is modular and every processing element may transfer data to and from the bus. However, the bus provides the only communications medium and consequently its bandwidth limits the useful size of such a machine. These machines are physically arranged with, typically, a backplane into which modules containing microprocessor units are plugged Difficulty may also be experienced in distributing electrical power to the elements of a large multiprocessor computer. One problem is created simply by the size of currents involved. A fully populated system can, for example, draw hundreds or even thousands, of Amps from the +5 volt power rail.

Handling currents this large, within an enclosure typical for such systems, requires the use of special techniques. Power supply units used to provide such heavy currents have a specified minimum load of typically 10% to 25% of the full rated load. This can create another difficulty in machines that are only partially populated as a dummy load must be provided.

Large power supply currents can also create variations in the ground potential in different parts of the system, which can cause a further difficulty since, unless special provision is made, these variations can affect detrimentally the fidelity of electrical signals that are transmitted across the system.

It is an object of the present invention to provide an economical, flexible alternative signal switching arrangement which overcomes the problems inherent in the prior art, noted above.

According to the present invention there is provided a signal switching arrangement for creating a signal path between two or more nodes of a multinodal system comprising: a plurality of node modules; a plurality of switching modules, each switching module being capable of selectively creating a signal path between two or more modules interconnected with said switching module, and; said node modules and switching modules each comprising means for enabling interconnection of a signal path between two or more modules.

Further according to the present invention there is provided a signal switching arrangement for electrically interconnecting two or more nodes of a multinodal system comprising: a plurality of substantially planar node modules each comprising at least one node of the system and one or more switching elements, the node modules being locatable such that the plane of any first node module is substantially parallel to the plane of any other node module; a plurality of substantially planar switching modules each comprising at least one switching element, the switching modules being locatable such that the plane of a first switching module is substantially parallel to the plane of any other switching module; ; the switching modules and node modules being locatable such that one edge of every switching module substantially intersects one edge of every node module, said node modules and said switching modules each comprising means for enabling electrical interconnection of two or more modules at a point of intersection.

Preferably, each node module holds several nodes of the system, which communicate with other nodes on the same node module, via a switching element located on the node module.

The switching element located on the node module is part of a larger network of switching elements. By using the switching elements located on switching modules to connect one node module with another node module, nodes located on physically separate node modules may communicate via an interconnecting switching module.

Each switching element and node of the arrangement may receive a control signal via a management link from a management module located elsewhere in the system, the control signals being distributed to each module via a management routing module.

Preferably, the management module is locatable in a similar manner to one of the node modules, and the management routing module is locatable in a similar manner to one of the switching modules, for ease of manufacture and use.

Another preferred feature of the present invention is that a separate power supply unit may be provided on each module, which has advantages for power supply distribution to the nodes and switching elements of the arrangement.

A specific embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a prior art signal switch, sometimes known as as a Butterfly network; Figure 2 shows schematically the connection of a node of the preferred embodiment of the present invention to four switching elements, each one from the outer rank of a Butterfly network as shown in Figure 1; Figure 3 is a block diagram of a complete node module of the preferred embodiment of the present invention; Figure 4 is a block diagram of a complete switching module of the preferred embodiment of the present invention; Figure 5 is a perspective drawing of a complete signal switching arrangement of the preferred embodiment of the present invention;; Figure 6 is a perspective drawing showing, in detail, an exploded view of the electrical interconnections between the node modules and switching modules shown in Figure 5.

In the preferred embodiment of the present invention, the nodes of the system are micro-processor units, such as Inmos T9000 Transputers, which are electrically interconnected by the signal switching arrangement to form a multiprocessor computer.

The switching elements are Inmos IMSC104s, 32-way routing switches which include a 32x32 crossbar switch, together with signal buffering, retiming and packet routing based on the packet header. These switching elements are distributed between the node modules and the switching modules, and, when these modules are connected together using connectors at the edge of each module, form a suitable signal switching network. The link protocol of these devices imposes a restriction on the way that they may be connected together. Input and output ports of each device are paired together and must be connected to a corresponding pair on another device.

Figure 1 shows a schematic diagram of a 3rank Butterfly network which comprises 48 individual switching elements such as Inmos IMSC104s, arranged into three ranks, each of sixteen elements, to form a 512-way routing switch.

The elements (31) of the central rank are located in the switching modules while one element (22) from either of the outer two ranks is located in each node module. Links (27), each representing a connection pair that contains a signal path in both directions, run between the node modules and switching modules to connect the switching elements in a network such that every element (31) in the central rank is connected to every element (22) in each of the outer ranks. Each switching element (22) of the outer ranks is connected by a link (26) to a maximum of sixteen nodes (not shown).

Inmos T9000 transputers have four communication links, so four separate Butterfly networks are provided. One switching element (22) from either of the outer ranks of each of the four networks is located on each node module. This is shown more clearly in Figure 2 where a node (21) is connected by four general purpose communication links (25) to four switching elements (22), one from each of the four Butterfly networks. Fifteen further nodes are connected in a similar manner to other links (26) on each of the switching elements. The remaining sixteen links (27) of each switching element go off-board to the switching modules and form a network as shown in Figure 1. Using suitable alternative switching elements or switching network may lead to a slightly different configuration.For example, using Inmos IMSC004s as switching elements requires at least one element from each of the outer ranks to be located on each node module.

The principal parts of a complete node module (20) are shown in Figure 3. Sixteen nodes (21) are each connected by one of their four general purpose communications links to each of the four switching elements (22). The sixteen remaining links (27) of each switching element are wired to connectors (14) located at the edge of the module. Thirty-two such node modules are provided; one for each switching element in the outer ranks of the Butterfly networks.

Also provided on each node module is a power supply unit (PSU) (23) that inputs electrical power from a connector at the edge of the module and outputs a regulated supply that is galvanically isolated from the input. This output supplies power for the other components of the module. A management link (24) is provided which is used to control and monitor the nodes and switching elements of the module. It is driven from a management module located elsewhere in the system.

The principal parts of a complete switching module (30) are shown in Figure 4. The communication links of four switching elements (31) are wired to connectors (14) located at the edge of the module.

Sixteen such switching modules are provided, one for each of the switching elements of the central rank of the Butterfly networks. In alternative embodiments, the switching module may contain switching elements which are all from the same Butterfly network, or from a combination of a number of Butterfly networks.

Also provided on each switching module is a power supply unit (PSU) (32) that inputs electrical power from a connector at the edge of the module and outputs a regulated supply that is galvanically isolated from the input. This output supplies power for the other components of the module. A management link (33), driven from a control module located elsewhere in the system, is also provided on each switching module (30), and is used to control and monitor the switching elements of the module.

As shown in Figure 5, the node modules (20) are stacked parallel to one another, and the switching modules (30), also stacked parallel to one another, are located such that the plane of the switching modules intersects the plane of the node modules at 900, but the modules themselves intersect end on and are connected by edge connectors on each module at each point of intersection.

In a further possible embodiment of the present invention, connectors (14) on the switching modules (30) may be located on all four edges of the switching module (30), such that separate stacks of node modules may connect with each of the four edges of the switching modules.

Alternatively, the switching modules may be non-rectangular, for example, circular, but all of similar shape and are arranged in a co-planar fashion so that the edges of the node modules may intersect with each of the switching modules. Equally, the position of the node modules and switching modules in this alternative embodiment may be reversed.

A backplane (10) as shown in Figure 5 may be used for increased strength and rigidity, to connect the switching modules (30) and the node modules (20).

Connectors (11) which have contacts on both sides of the backplane (10) are provided such that a plurality of node modules (20) mate with one side of the connectors and switching modules (30) mate with the other side. Figure 5 shows a preferred embodiment in which one edge of the node modules (20) are connected via a backplane (10) to one edge of the switching modules (30).

Also shown in Figure 5 are a management module (40), located in a similar manner to a processing module (20), and a management routing module (41), located in a similar manner to a switching module (20); which together provide control and monitoring of the system.

An exploded view of the electrical connectors used in the preferred embodiment shown in Figure 5, are shown in detail in Figure 6. Fitted to the backplane (10) are plugs (11) with extended rear pins and shrouds (12) which protect the pins from accidental damage.

The plugs and shrouds may be provided with a suitable locking mechanism (13) so that, when assembled, both parts are held together. Fitted to the node modules (20) and switching modules (30) are right-angled sockets (14) which mate with either side of the plugs.

The arrangement of the contacts has rotational symmetry allowing the sockets to mate in more than one orientation with the plugs.

Thus, an improved signal switching arrangement is disclosed which overcomes the problems of the prior art by using separate node modules and switching modules, and by connecting these modules as described, using edge connectors on each module.

It is envisaged that the present invention may be readily applied to applications other than the preferred embodiment mentioned above, in the field of signal switching apparatus, for example, by substituting the nodes of the arrangement (Inmos T9000 Transputers) or switching elements (Inmos IMSC104s) for appropriate alternatives, to fulfil a particular application, without departing from the scope of the present invention.

Claims

1. A signal switching arrangement for creating a signal path between two or more nodes of a multinodal system comprising: a plurality of node modules; a plurality of switching modules, each switching module being capable of selectively creating a signal path between two or more modules interconnected with said switching module, and; said node modules and switching modules each comprising means for enabling interconnection of a signal path between two or more modules.

2. A signal switching arrangement as claimed in claim 1, in which said switching modules are locatable such that at least one edge of every switching module intersects one edge of every node module, and every switching module is capable of selectively creating a signal path between any first node module and any one or more other node modules.

3. A signal switching arrangement as claimed in any preceding claim, in which each node module comprises at least one node and none or more switching elements.

4. A signal switching arrangement as claimed in any preceding claim, in which each switching module comprises at least one switching element.

5. A signal switching arrangement as claimed in claim 4, in which the switching elements are connected so as to form a network which is capable of creating a signal path between any first node and any one or more other nodes of the system.

6 A signal switching arrangement, as claimed in any preceding claim, in which the means for enabling interconnection of a said path between two or more modules comprise readily separable electrical connectors.

7. A signal switching arrangement as claimed in any preceding claim, in which the means for enabling interconnection of a signal path between two or more modules are mounted on or through a rigid backplane.

8. A signal switching arrangement as claimed in any preceding claim, in which the switching modules are located in a different planar orientation to the node modules.

9. A signal switching arrangement as claimed in any preceding claim, in which; the node modules are substantially flat and are locatable such that the flat surfaces of said node modules are in substantially parallel planes to one another; the switching modules are substantially flat and locatable such that the flat surfaces of such switching modules lie in substantially parallel planes to one another; said node modules and switching modules are locatable such that at least one edge of every switching module substantially intersects at least one edge of every node module; and means for enabling the interconnection of a signal path between two or more nodes is provided at each point of intersection.

10. A signal switching arrangement as claimed in claim 9, in which the plane of said parallel switching modules is at 900 to the plane of said node modules, such that one edge of every switching module substantially intersects one edge of every node module at 900.

11. A signal switching arrangement as claimed in claim 10 in which said switching modules are substantially flat and rectangular, and four sets of substantially parallel node modules are provided, each intersecting one side of said parallel plane switching modules.

12. A signal switching arrangement for electrically interconnecting two or more nodes of a multinodal system comprising: a plurality of substantially planar node modules each comprising at least one node of the system and one or more switching elements, the node modules being locatable such that the plane of any first node module is substantially parallel to the plane of any other node module; a plurality of substantially planar switching modules each comprising at least one switching element, the switching modules being locatable such that the plane of a first switching module is substantially parallel to the plane of any other switching module;; the switching modules and node modules being locatable such that one edge of every switching module substantially intersects one edge of every node module, said node modules and said switching modules each comprising means for enabling electrical interconnection of two or more modules at a point of intersection.

13. A signal switching arrangement as claimed in any of claims 4 to 12 in which the switching elements are interconnected so as to form a multi-rank Butterfly network

14. A signal switching arrangement as claimed in claim 13, in which said Butterfly network has three ranks.

15. A signal switching arrangement as claimed in claim 13 or claim 14, in which the switching elements of the Butterfly network are distributed between the node modules and the switching modules, such that each node module contains one or more switching elements from the outermost ranks of the Butterfly network and each switching module contains one or more switching elements from the central ranks of the Butterfly network.

16. A signal switching arrangement as claimed in claim 15 in which each node module comprises one switching element from the outer rank of said Butterfly network, such that one node module is provided for each switching element of the outer rank of the Butterfly network.

17. A signal switching arrangement as claimed in claim 16, in which the number of node modules is 32.

18. A signal switching arrangement as claimed in claim 15, in which each switching module comprises one switching element from the central rank of said Butterfly network, such that one node module is provided for each switching element of the central rank of the Butterfly network.

19. A signal switching arrangement as claimed in claim 18 in which the number of switching modules is 16.

20. A signal switching arrangement as claimed in any preceding claim, in which each node module has a plurality of nodes, each connected to a single switching element on that module, such that local communication may be effected using said switching element, said switching element also being a member of the outer rank of a Butterfly network, through which communication to any other node located on any other node module may be effected.

21. A signal switching arrangement as claimed in any preceding claim, in which a plurality of switching networks are provided, such that each node is connected to each of said plurality of switching networks, by one or more switching elements from each of said switching networks.

22. A signal switching arrangement as claimed in claim 20, in which each node comprises a plurality of communications links and a separate 3-rank Butterfly network is provided for each link.

23. A signal switching arrangement as claimed in claim 22 in which each node has four communication links and four separate 3- rank Butterfly networks are provided, each node module comprising four switching elements, one from the outer rank of each 3-rank Butterfly network, and each switching module comprising four switching elements, one from the central rank of each 3-rank Butterfly network.

24. A signal switching arrangement as claimed in any preceding claim wherein said arrangement comprises management means for the control and monitoring of the nodes and switching elements of the arrangement, the management means incorporating a management module, and management routing means for the distribution of management control signals to the nodes and switching elements of the arrangement.

25. A signal switching arrangement as claimed in claim 24 in which the management module is locatable in a similar manner to one of said node modules.

26. A signal switching arrangement as claimed in claim 24 or claim 25 in which said management routing means is locatable in a similar manner to one of said switching modules.

27. A signal switching arrangement as claimed in any preceding claim, said arrangement providing individual power supply units for the local distribution of power to said nodes and switching elements, the power supply units being locatable on the node modules and the switching modules.

28. A signal switching arrangement as claimed in any preceding claim in which each node is an electronic processing unit and the switching elements are arranged to form a multiprocessor computer.

29. A signal switching arrangement substantially as hereinbefore described with reference to the accompanying drawings.