Two designs of 4-disjoint gamma interconnection networks for reliable data communication in a tightly coupled, large-scale, multiprocessor system are described in this paper. These two designs provide four disjoint paths for each source-destination pair and can tolerate three switches/link failures in intermediate interconnection layers. A higher number of alternate and disjoint paths for every source to its destination serves to provide better fault tolerance and reliability in a network.

This paper thoroughly describes the multistage interconnection networks, ranging from 2-disjoint path gamma interconnection networks (2DGIN), to 3-disjoint gamma interconnection networks (3DGIN), to 4-disjoint gamma interconnection networks (4DGIN). Except for a few obvious errors, the description is generally easy to follow. However, these errors hinder understanding of the paper. These errors are as follows.

In section 3.2, “Routing,” the sentence, “The binary redundant forms for the tag value of 2 are (0, 1, 0), (0, -1, 1) and (0, -1, -1)” contradicts the standard definition of binary redundant forms. I believe this sentence should read, “The binary redundant forms for the tag value of 2 are (0, 1, 0) and (1, -1, 0).” In table 3, the sizes of crossbar switches for 3DGIN are incorrect. This error is obvious if we refer to figure 7.

It seems that the authors have only focused on creating multiple disjoint paths between a pair of source-destination points while constraining the size of the entire interconnection network. The key issue that has been missed is the relationship between the redundancy in the interconnection network and the number of concurrent paths for multiple pairs of source-destination points. An appropriate degree of redundancy makes it possible to support concurrent paths despite crossbar failure.

Overall, this paper has not made a significant contribution to the issue of reliable data communication in a tightly coupled, large-scale, multiprocessor system.