Reliability Analysis of Multistage Interconnection Networks S. Rajkumar * † and Neeraj Kumar Goyal Multistage interconnection networks (MINs) are widely used for reliable data communication in tightly coupled large-scale multiprocessor systems. Reliability evaluation of interconnection networks is still a challenge owing to high complexity. Need of reliability evaluation for MINs is quite evident as these measures provide user-oriented performance. Terminal pair reliability (TPR) is the most commonly used reliability performance index of MINs. This paper provides a global view of different reliability measures and approaches for evaluation of these measures. Based on the critical literature review, shortcomings are identified and analyzed. Then the multi-variable inversion algorithm is applied to evaluate the reliability of one of the most common MINs, namely, Omega network, in a compact form. Terminal, broadcast, and network reliability for the Omega, Omega with an additional stage (Omega+), and Omega with two additional stages (Omega+2) systems are analyzed and compared. Then we extend our work to trace the minimal path sets of various MINs, and terminal pair reliabilities are evaluated and compared. Copyright © 2015 John Wiley & Sons, Ltd. Keywords: computer network reliability; path sets; multistage interconnection networks (MINs) 1. Introduction M ultiprocessor environment involves interconnecting a large number of processor or processor-memory modules. 1–14 It is a complicated task as it has to address issues such as connectivity, latency, bandwidth, cost, scalability, and reliability. Numerous approaches of network interconnection had been proposed, ranging from a single bus to fully connected architecture. According to the topology, the interconnection networks can be classified into shared medium, direct, indirect, and hybrid interconnection networks. Among indirect networks, multistage interconnection network (MIN) is an intermediate and alternative interconnection network between shared bus and crossbar for large multiprocessor systems. 3 They provide higher performance than the shared bus and lower switching cost than crossbar network. MINs having log 2 N (N is the number of input and output nodes) switching stages that are widely used in parallel and distributed systems, networks-on-chips, broadband communications, and very large-scale integration implementation. 4–8 MIN consists of layers of switching elements (SEs) connected together in a predefined topology, providing the connectivity between input and output. MIN falls within the category of indirect network. Multistage interconnection network has been extensively used in circuit switching and packet switching networks with the introduction of buffered switches. MIN is an interconnection system that consists of multiple layers of interlinked SEs arranged in a predefined topology, allowing processor and memory modules to communicate with each other. 13–17 It has been adopted in many fields, mainly in computer networking, telephone network, and multiprocessor environment. MINs are fault tolerant and cost-effective and provide low transmission delay using multistage switching fabrics routes to perform multiple communication tasks concurrently. 2 An MIN connects N inputs (sources) to N outputs (destinations) through a number of switch stages and is referred to as an N × N MIN. The parameter N is called the size of the network. Various topologies of MINs have been proposed in the last few decades. 1–42 Most of these topologies are either unique path or multipath networks. MINs attempts to reduce cost and decrease the diameter where diameter is the longest path any two nodes. The banyan network, 18 delta networks, 13 binary n-cube network, 14 Butterfly, 8 Omega network, 16 shuffle-exchange network (SEN), 21 and baseline 5–7 are some popular MIN architectures. In this research, the multistage Omega network and extra-stage Omega networks will be examined because they have been widely accepted as a practical interconnection system owing to the size of their SEs and uncomplicated configuration. Being a self-routing network, Omega network provides only one path between any source–destination node pairs using 2 × 2 switches as basic elements. Reliability Engineering Centre, IIT Kharagpur, West Bengal, India *Correspondence to: S. Rajkumar, Reliability Engineering Centre, IIT Kharagpur, West Bengal, India. † E-mail: s.rajkumar@iitkgp.ac.in Copyright © 2015 John Wiley & Sons, Ltd. Qual. Reliab. Engng. Int. 2015 Short Communication (wileyonlinelibrary.com) DOI: 10.1002/qre.1941 Published online in Wiley Online Library