Co-Leader Based Leader Election Algorithm in Distributed Environment

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1 Co-Leader Based Leader Election Algorithm in Distributed Environment Gajendra Tyagi, Ankit Mundra, Jitendra Kr. Tyagi and Nitin Rakesh Department of Computer Science and Engineering, Jaypee University of Information Technology, Waknaghat, P.O. Waknaghat, Tehkandaghat, Distt. Solan. Abstract. In a distributed environment, several independent nodes work together by exchanging messages to each other. To achieve synchronization and co-ordination among the nodes, there is a need to elect one leader node. Previously several algorithms have been proposed,one of the classical and well-known algorithms to elect the leader node is bully algorithm. Ring algorithm is another modified version of bully algorithm. But these algorithms are having a large number of messages during election process. Till now several amendments are done over the bully algorithm to reduce the number of messages in the leader election process. This paper presents the concept of co-leader based leader election mechanism by which the number of messages can be greatly reduced and hence can reduce network traffic. Further, we have evaluated the performance of our proposed approach by considering the testbed of 10, 100 and 1000 nodes and shown the comparative analysis. Keywords: Bully algorithm, Leader-election, Co-leader, Message passing. 1. Introduction In a distributed environment, several nodes work together as a single unit therefore it is much needed to have the coordination among all these nodes. It is the leader node which is assigned with this responsibility and its role is very crucial in the distributed environment and also in communication network [1 5]. One of the main responsibilities of the leader node is to make sure about the synchronization between different devices. There are various parameters which are generally taken into consideration during the election of leader node like maximum node degree means maximum number of connections to other nodes is considered as having the highest priority [6]. One more parameter is their lifetime means a node having the maximum lifetime is preferred. There are a number of algorithms proposed till now. Each algorithm has its own strategy and parameters to select the leader. However, all these algorithms have successfully done their task of electing the leader, but these are having some disadvantages of large number of redundant election message. In this paper, we have tried to reduce the number of election messages and simultaneous election initiation by introducing the concept of co-leader. This paper is organized in five sections. In section 2, we have examined the previous related work of leader selection algorithms. Section 3 would present the proposed approach and its procedure for leader selection. In section 4, comparison with the previous algorithm is done. Finally, conclusion is given in section 5. ICC-2014 Editors: K. R. Venugopal and S. C. Lingareddy pp

2 Gajendra Tyagi, et al. Figure Related Work Till now, various algorithms have been proposed for the selection of leader. One of the most famous and well known algorithms for this purpose is bully algorithm which was proposed by Garcia-Molina. Bully algorithm and some of its enhanced versions are discussed below. 2.1 Bully Algorithm When a node p knows about the failure of coordinator by the timeout mechanism, it executes the bully algorithm [7]. An election message is sent by node p to all the other nodes having higher id with respect to it. Figure 1(a) Node 3 is detecting the failure of leader node. (b) Node 3 is initiating an election to select the leader node by sending message to higher id nodes. (c) Higher id nodes 4, 5 and 6 are replying with OK message to initiate the election. (d) All the higher id nodes initiated the election. (e) Node 6 is sending an OK message to node 5 to stop the election. (f) Finally Node 6 broadcasting the coordinate message to all nodes. Bully algorithm got very much popularity because of its successful operation of electing the leader. But it was using a large number of message passing during the process. 2.2 Consensus Based Leader Election Algorithm In this algorithm, procedure of electing new leader is stats when a node in the network detects that the current leader node has failed. Afterwards, it starts sending the election message to all the higher priority nodes. These nodes after receiving the election message confirm the failure of leader node by 262

3 Co-Leader Based Leader Election Algorithm in Distributed Environment Figure 2. sending the CHECK EXIST message to the failed leader. In Figure 2(a). Node 4 is detecting the failure of leader and sending the election message to node 5 and 6. In 2(b) node 5 and 6 are confirming the failure of node 7. In 2(c) node 5 and 6 are sending OK message to node 4(d) node 4 is grating the node 6. In 2(d) node 6 is sending the proposal. In 2(e) ACCEPT message is received by node 6. In 2(f) node 6 is broadcasting the COORDINATOR message. The number of messages got reduced in this algorithm in comparison to the bully algorithm [6,8]. But a further reduction is possible, which is discussed below in section 3 rd and comparison with the previous algorithm in shown below in section Proposed Approach This algorithm is established on some basic assumptions which are: It is a synchronous system and each node is assigned a unique identification number in an increasing order. A timeout mechanism is used to identify the failure of nodes. Each node has the knowledge of identification number of all other nodes. In the election, a node with the lowest identification number is elected as the leader node. The node with the second lowest identification number is elected as the co-leader. A failed node can recover and rejoin the system at any time. A number of messages are used in this algorithm namely ELECTION, PROPOSAL, VERIFY, LEADER,CO LEADER, SENDER ALIVE and OK. 263

4 Gajendra Tyagi, et al. Figure 3. (a) Leader failure is detected by node 4. (b) Node 4 is sending the proposal to node 2 which is a co-leader. (c) Co-leader is verifying the failure of leader node (d) After verification, co-leader is announcing the leadership to all nodes. (e) All the nodes are replying to new leader. (f) Leader is broadcasting the new co-leader which is node Execution of Proposed Algorithm As it is already assumed that the failure of nodes are identified by a timeout mechanism, and all the nodes are assigned the id in an increasing order. Suppose there is a system, in which there are seven live nodes. Each node is having a unique id and the node with id 1 is the leader of the system. The node with id 2 is the co-leader of the system. Suppose at any instant of time, leader got crashed and this failure is detected by node 4. The node 4 will immediately send the PROPOSAL message to the co-leader of the system to become the new leader. Node 2 i.e. co-leader will verify the failure of leader by sending a VERIFY Message. If no response is received from Figure 4. Comparative analysis. the leader within a predefined time, the co-leader will be sure of the leader failure. The co-leader will then broadcast the LEADER message to all the nodes and waits for the OK message. All the live nodes will acknowledge the new leader by sending the OK message along with their id. In this way, this new leader i.e. node 2 will get to know about the next minimum id. Then the new leader will broadcast a CO LEADER message to all the nodes telling them about the new co-leader. The whole procedure is illustrated in the Figure

5 Co-Leader Based Leader Election Algorithm in Distributed Environment Table 1. Algorithm: Co-leader based leader selection algorithm. Table 2. Number of messages comparison with previous algorithms. 4. Algorithm and Performance Evaluation In this section we have evaluate the performance of our proposed approach against the previous approaches in terms of number of message passing. We have implemented the testbed for 10, 100 and 1000 nodes using MPI framework. After the implementation we have computed the number of messages required by bully algorithm, consensus algorithm and our proposed algorithm (shown in Table 1 and 2). 5. Conclusion In this paper we have proposed the co-leader based leader selection algorithm for distributed communication environment. Our proposed approach provides the robust mechanism for electing the leader node 265

6 Gajendra Tyagi, et al. among the several candidates with less number of election messages. We have also shown the performance of our approach with the previous approaches and prove that our approach is more robust and required less number of messages. Because of less number of messages in the network the overall performance is increased. References [1] H. Abu-Amar and J. Lokre, Election In Asyncronous Complete Network With Intermitted Link Failures, IEEE Transaction on Computers, vol. 43, no. 7, pp , (1994). [2] J. Brunkreef, J. P. Katoen and S. Mauw, Design and Analysis of Dynamic Leader Election Protocols in Broadcast Network, Distributed Computing, vol. 9, no. 4, pp , (1996). [3] H. M. Sayeed, M. Abu-Amara and H. Abu-Avara, OptimalAsynchronous Agreement and Leader Election Algorithm for Complete Networks with Byzantine Faulty Links, Distributed Computing, vol. 9, no. 3, pp , (1995). [4] Sung-Hoon-Park, Yoon Kim and Jeoung Sun Hwang An Efficient Algorithm for Leader-Election in Synchrous Distributed Systems, IEEE Transaction on Computers, vol. 43, no. 7, pp , (1999). [5] G. Singh, Leader Election in the Presence of Link Failures IEEE Transaction on Parallel and Distributed Systems, vol. 7, no. 3, pp , March (1996). [6] Hsu-Chia Cahng and Chi-Chun Lo, A Consensus-Based Leader Election Algorithm for Wireless Ad Hoc Networks. [7] H. Garcia-Molina, Elections in Distributed Computing System, IEEE Transaction Computer, vol. C-31, pp , January (1982). [8] S. H. Park, Y. Kim and J. S. Hwang, An efficient algorithm for leader-election in synchronous distributed systems, IEEE TENCON, pp , (1999). 266

Leader Election Algorithms in Distributed Systems

Leader Election Algorithms in Distributed Systems Available Online at www.ijcsmc.com International Journal of Computer Science and Mobile Computing A Monthly Journal of Computer Science and Information Technology IJCSMC, Vol. 3, Issue. 6, June 2014, pg.374