Maximum and Maximal Weight Matching Dispatching Schemes for MSM Clos-Network Packet Switches

Roberto ROJAS-CESSA  Eiji OKI  H. Jonathan CHAO  

IEICE TRANSACTIONS on Communications   Vol.E93-B   No.2   pp.297-304
Publication Date: 2010/02/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E93.B.297
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Switching for Communications
packet switch,  clos-network,  dispatching,  throughput,  maximum-weight matching,  

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The scalability of three-stage Clos-network packet switches makes them an attractive approach in implementing large-size packet switches. However, the configuration time of Clos-network switches depends on both the buffering strategy used and the adopted configuration process. To reduce configuration time, this paper focuses on the so-called Memory-Space-Memory (MSM) Clos-network packet switch, where the switch modules in the first and third stages use memory to support resolution of output port contention. The configuration of these switches is then based on a process to dispatch cells from the first-stage modules to the third-stage modules. Therefore, the throughput of an MSM Clos-network switch depends on the dispatching scheme used. This paper introduces a cell dispatching scheme, called maximum weight matching dispatching (MWMD) scheme, for MSM Clos-network switches and a request queue structure in the first-stage modules. The MWMD scheme performs maximum weight matching, similar to that used for input-queued single-stage packet switches, that in combination with the request queues can achieve 100% throughput under independent and identical admissible traffic. This high throughput can be achieved without allocating buffers in the second stage and without expanding the second stage of this three-stage packet switch. A low-complexity dispatching scheme, the maximal oldest-cell-first matching dispatching (MOMD) scheme, is also introduced as an alternative to MWMD. The performance evaluation in this paper shows that MOMD achieves high throughput under unbalanced traffic through the execution of a finite number of iterations.