Clos-Knockout: A Large-Scale Modular Multicast ATM Switch

King-Sun CHAN  Sammy CHAN  Kwan Lawrence YEUNG  King-Tim KO  Eric W. M. WONG  

IEICE TRANSACTIONS on Communications   Vol.E81-B    No.2    pp.266-275
Publication Date: 1998/02/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on ATM Switching Systems for future B-ISDN)
Category: Multicasting in ATM switch
ATM switch architecture,  multicast,  self-routing,  

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A large-scale modular multicast ATM switch based on a three-stage Clos network architecture is proposed and its performance is studied in this paper. The complexity of our proposed switch is NN if the switch size is NN. The first stage of the proposed multicast switch consists of n sorting modules, where n=N. Each sorting module has n inputs and n outputs and is responsible for traffic distribution. The second and third stages consist of modified Knockout switches which are responsible for packet replication and switching. Although it is a multipath network, cell sequence is preserved because only output buffers are used in this architecture. The proposed multicast switch has the following advantages: 1) it is modular and suitable for large scale deployment; 2) no dedicated copy network is required since copying and switching are performed simultaneously; 3) two-stage packet replication is used which gives a maximum fan-out of n2; 4) translation tables are distributed which gives manageable table sizes; 5) high throughput performance for both uniform and nonuniform input traffic; 6) self-routing scheme is used. The performance of the switch under uniform and non-uniform input traffic is studied and numerical examples demonstrate that the cell loss probability is significantly improved when the distribution network is used. In a particular example, it is shown that for the largest cell loss probability in the second stage to be less then 10-11, the knockout expander, with the use of the distribution network, needs only be larger than 6. On the other hand, without the distribution network, the knockout expander must be larger than 13.