Performance Enhancement in Recursive Copy Networks for Multicast ATM Switching: A Simple Flow Control Scheme

Wen De ZHONG  Yoshikuni ONOZATO  Jaidev KANIYIL  

IEICE TRANSACTIONS on Communications   Vol.E77-B   No.1   pp.28-34
Publication Date: 1994/01/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Switching and Communication Processing
multicast ATM switching,  recursive copy network,  flow control,  back-pressure,  buffer overflow,  

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As promising copy networks of very large multicast switching networks for Broadband ISDN, multi-stage Recursive Copy Networks (RCN) have been proposed recently. In the multicast switch structure, the RCN precedes a point-to-point switch. At an RCN, all the copies of a master cell are generated recursively, i.e., a few copies of the master cell are made initially, and by considering each of these copies to be master cells, more copies are made which, in turn, are again considered to be master cells to make still more copies, the process thus progressing recursively till all the required copies are made. By this principle of recursive generation of copies, the number of copies that can be generated is independent of the hardware size of the RCN. A limitation of RCNs is that buffer sizes at all stages except the first stage have to be large so as to keep the cell loss due to buffer overflow within desired limits. This paper inspects a flow control scheme by which the probability of buffer overflow can be kept low, even though the buffer sizes at later stages are not large. Under this flow control procedure, a cell is not transmitted from a stage to the succeeding stage, if the occupancy level of the buffer of the succeeding stage exceeds a threshold. We study by simulation the performance aspects of such a flow control scheme in RCNs under cut-through switching scheme and under store-and-forward switching scheme. At high load intensities, the overflow probability can be reduced by an order of magnitude in 2-stage RCNs and by two orders of magnitude in 3-stage RCNs. To restrict the overflow probability within a given limit, the required buffer size is less under flow control than under no flow control. The implementation of the flow control is simple and the control overhead is small, thereby making the scheme attractive for implementation in high speed switching environments. Further, the proposed flow control scheme does not disturb the cell sequence.