MODIFIED BULLY ELECTION ALGORITHM IN DISTRIBUTED SYSTEMS M. S. Kordafshari, M. Gholipour, M.Jahanshahi, A.T. Haghighat, Department of Electrical, Computer & IT, Islamic Azad University, Qazvin Branch, Qazvin, Iran Atomic Energy Organization of Iran (AEOI), NPPD, Tehran, Iran Abstract: Leader election is an important problem in distributed computing, and it is applied in many scientific fields such as communication network [1,2,3,4,5], centralized mutual exclusion algorithm [6,7], centralized control IPC, Berkeley algorithm, etc. Synchronization between processes often requires one process acting as a coordinator. The coordinator might not remain the same, because might get crashed. Bully election algorithm is one of the classic methods which is used to determine the process with highest priority number as the coordinator. In this paper, we will discuss the drawbacks of Garcia_Molina’s Bully algorithm and then we will present an optimized method for the Bully algorithm called modified bully algorithm. Our analytical simulation shows that, our algorithm is more efficient rather than the Bully algorithm with fewer message passing and fewer stages. Key-word: Bully algorithm, modified Bully algorithm, election, distributed systems, Message passing, coordinator 1. Introduction Election of a leader is a fundamental problem in distributed computing. It has been the subject of intensive research since its importance was first articulated by Gerard Le Lann [8] in 1977. The practical importance of elections in a distributed computing is further emphasized by Garcia_Molina’s Bully algorithm [9] in 1982. Based on a network topology, to elect a high- priority leader, many kinds of leader election algorithm have been presented. There are some algorithms about the election such as Fredrickson and Lynch [10], Singh and Kurose [11], etc. Other algorithms such as B.Awerbuch algorithm [12], Gallage & Humblet algorithm [13], Gafini algorithm [14], Chin & Ting Algorithm [15], Chow & Luo Algorithm [16] are based on spanning tree. Also some related papers proposed based on Ring Algorithm for b