Multiplex communications – Wide area network – Packet switching
Patent
1993-04-08
1996-03-05
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
3408258, H04L 1256
Patent
active
054973694
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to multicast switch circuits for use in packet switches operating to transfer data in an asynchronous transfer mode (ATM) network.
With the arrival of optical fibre communication links, broadband packet networks are required to handle and transfer packets of information such as data, voice, and video at high speed from multiple inputs to multiple outputs. Multicast packet switches can be employed in such networks and may consist of two parts--a multicast fabric wherein the number of copies of a packet are created from a single input packet, and a routing fabric wherein the required number of packets as produced by the multicast fabric are received and directed to the correct output addresses.
BACKGROUND ART
Various multicast packet switches have been proposed in the past, for example those by J. S. Turner (IEEE Transactions on Communications, 36, no. 6, June 1988, pp.734-743) and T. T. Lee (IEEE Journal on Selected Areas in Communications, 6, no. 9, December 1988, pp.1455-1467). Such switches are normally modular in design and are intended for implementation on a large scale, coupled for example in a delta network, so as to enable large numbers of inputs/outputs to be handled.
A problem with such multicast fabrics is how to handle contention at nodes within the fabric, where collisions can occur between cells (packets) contending for the same paths within the fabric. Blocking arises when a cell is unsuccessful in gaining control of a suitable path through the fabric. A means must be provided for enabling the cell to retry transmission so as to complete its passage through the switches. Lee (ibid) describes a particular form of non-blocking multicast circuit, whereas Turner (ibid) handles blocking by providing buffers for the cells at the nodes within the multicast fabric and which hold the cells until a successful retry in transmission through further nodes in the fabric can be made.
The present invention is concerned with switches for multicast fabrics which handle cell replication and blocking in a novel way. They can be produced cheaply in small gate arrays, and therefore are suitable for production in modular form to enable multi-input/output packet switches to be produced.
DISCLOSURE OF THE INVENTION
According to the invention there is provided a multicast switch element suitable for connection to a plurality of similar such elements in a matrix to form a multicast switch fabric, said element having a plurality of inputs and a plurality of outputs and a switch therebetween for passing through to the outputs cells of information received at the inputs and for replicating copies of the cell information in accordance with instructions associated with the cell information, and means associated with the switch for decoding said instructions in two sections: one section determining the number of times the cell information is to be replicated within the switch, and the other section determining whether or not the cell is to be replicated fully in any subsequent switch elements to which the element may be connected in the multicast switch fabric.
According to the invention there is also provided a multicast switch fabric having an M.times.M matrix of connected switch elements as specified in the preceding paragraph, an input port and an output port associated with each input and output respectively of the fabric, each said input port having an input buffer for storing a cell for transmission through the fabric and means for retaining any such cell in said buffer until cell transmission is successful.
Preferably the switch element is constructed as a small modular unit, e.g. as a 2.times.2 switch, which can be coupled with many similar elements to form a matrix such as a delta network.
In accordance with the invention the incoming cell is buffered at an input port of the multicast fabric where it remains until the cell can be successfully transmitted through the network of switch elements, or until a maximum number of retries at transmission is reached. A successio
REFERENCES:
patent: 4734907 (1988-03-01), Turner
patent: 4813038 (1989-03-01), Lee
patent: 4866702 (1989-09-01), Shimizu et al.
patent: 4932020 (1990-06-01), Pashan et al.
patent: 5179551 (1993-01-01), Turner
patent: 5258752 (1993-11-01), Fukaya et al.
A survey of Fast Packet Switches, by Andrew R. Jacob, Computer Communication Review, vol. 20, No. 1, pp. 54-64, Jan. 1990.
Hewlett--Packard Company
Safourek Benedict V.
Ton Dang
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