Multiplex communications – Wide area network – Packet switching
Patent
1990-10-12
1993-12-07
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 854, 370 855, 370 856, 370 859, H04Q 1104
Patent
active
052688968
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a communication switching element with buffer means associated with a plurality of signal inputs and signal outputs.
BACKGROUND ART
In such known switching elements buffer means can generally be associated with the signal inputs and/or with the signal outputs. In case they are associated with the signal inputs, when several signals arrive at a same signal input and have to be transmitted to a same signal output, the corresponding input buffer means may only be emptied at the signal transmission speed used on this signal output. This means that the following signals also arriving at this signal input and to be transmitted to another signal output have to wait for the completion of the transmission of the above preceding signals prior to being transmitted to their destination signal output even if the latter is not used.
In the switching element known from the PCT application published under No WO87/004579 and used in an Asynchronous Time Division (ATD) packet or cell switching system, buffer means associated with the signal outputs are preferred to avoid such input saturation. However, it requires at each of its signal outputs relatively large buffer means able to store signals simultaneously transmitted by all its signal inputs. Moreover, in order to be able to accept the signals from all the signal inputs, this known switching element operates at a speed or bitrate equal to the sum of the bitrates at which these signals are supplied at their respective signal input. As a result, the complexity of the element is increased.
A solution to reduce this switching speed and accordingly to decrease the complexity of the switching element is for instance proposed in the PCT/EP88/00212 application filed on Mar. 11, 1988 and consists in subdividing each of the input signals into a number of parts, particularly sub packets in an AID system. Thus, the switching speed of the element is also divided by the same number. However, additional circuits required to realise such subdivision and to combine these parts into an output signal also contribute to the complexity of the switching element.
In the article: "Packet Switching Interconnection Networks for Modular Systems" by D. M. Dias et al published in IEEE-COMPUTER of December 1981, pages 43 to 53, and more particularly on page 45 thereof, delta networks are considered wherein the links between stages of a packet switching network contain data buffers organized as first-in-first-out queues and each able to hold one or more packets. In this way the two signal inputs and the two signal outputs of a binary switching element part of an intermediate stage are each associated with such a buffer. Nevertheless, blocking can still occur for such a switching element when the buffer at one of its output terminals is full.
In the article "THE KNOCKOUT SWITCH: A SIMPLE, MODULAR ARCHITECTURE FOR HIGH-PERFORMANCE PACKET SWITCHING" by Y. S. Yeh et al published in the proceedings of ISS '87 pages 0801 to 0808 as well as in the European patent application by the same inventors published under No. 0256702, a so-called N-input, N-output "knockout" packet switch uses N output interface units, each with N packet filters associated with the N signal inputs, a concentrator which achieves an N to L concentration, with L<<N, and an output buffer in order to have a lost packet rate as small as desired. However, if more than L packets or cells for the same signal output arrive simultaneously on the signal inputs, the extra packets are lost, even at a low transmission rate. Moreover, the modularity advantage of this known system increasing with the size thereof, it will preferably be used in large switching systems.
The present invention more particularly relates to a communication switching element for transferring digital signals, grouped in cells, from a plurality of signal inputs to a plurality of signal outputs, said switching element including a plurality of buffer means each associated and permanently dedicated to a distinct connecti
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S. Nojima, E. Tsutsui, H. Fukuda, M. Hashimoto, "Integrated Services Packet Network Using Bus Matrix Switch," IEEE Journal, No. 8, Oct. 1987 (pp. 1284-1292).
Y. S. Yeh, "The Knockout Switch: A Simple, Modular . . . ", AT&T Bell Labs., IEEE Proceedings, New Jersey, Dec. 1987, pp. 801-808.
D. M. Dias, "Packet Switching Interconnection . . . ", IEEE Computer, Dec., 1981, pp. 43-52.
ALCATEL N.V.
Blum Russell W.
Olms Douglas W.
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