ISSN(Online): 2320-9801 ISSN (Print): 2320-9798 International Journal of Innovative Research in Computer and Communication Engineering (An ISO 3297: 2007 Certified Organization) Vol. 2, Issue 7, July 2014 Copyright to IJIRCCE www.ijircce.com 4927 Reliability in MAC Protocols for Wireless Sensor Networks: A Survey Nicholas N. Karekwaivanane 1 , Wilson Bakasa 2 , Kudakwashe Zvarevashe 3 M Tech Student, Dept of CSE, Jawaharlal Nehru Technological University, Hyderabad, India 1 M Tech Student, Dept of CSE, Jawaharlal Nehru Technological University, Hyderabad, India 2 M Tech Student, Dept of CSE, Jawaharlal Nehru Technological University, Hyderabad, India 3 ABSTRACT: The field of wireless sensor networks has received widespread acceptance because of the ease deployment of nodes, no prior installation of infrastructure before deployment and low cost of operation. This has caused research in WSN to diversify and not only focus on energy conservation but to also look at ways to enhance the data performance of the network. QoS parameters such as reliability, loss, latency and bandwidth are now at the center stage of research. This paper focused on reliability in wireless sensor networks. A survey is performed on existing MAC protocols that provide reliability and they shall be classified according to the nature of the reliability they provide. There are protocols that provide node to node reliability and those that provide end to end reliability. We shall then analyze challenges associated with these existing mechanisms then propose future research directions. KEYWORDS: Wireless Sensor Network; Reliability; MAC Protocols, QoS, Survey I. INTRODUCTION Therehas been a marked increase in the number of applications for wireless sensor networks in recent years. This can be attributed to factors such as the low cost, no upfront setup in the environment prior to deployment, the ability to be deployed in adhoc fashion and still manage to communicate without challenges amongst many others. Initial research was targeted at maximizing the network lifetime whilst trading off factors such as the bandwidth, latency, reliability and loss. New application are now making demands that have shifted research to other areas such as the data transport performance. Reliability is one such factor and we are going to discuss in this paper. The MAC layer is the most important layer in the protocol stack for WSNs because most control mechanisms are implemented in this layer. In applications where strict data delivery must be enforced mechanisms must be put in place to ensure that data is delivered in a reliable manner. This paper is going to focus on MAC layer protocols that provide reliability. The remainder of this article is structured as follows: Reliability and classification of reliable protocols are discussed in section II. Section III discusses approaches taken by various MAC protocols to achieve reliability. In section IV we highlight challenges faced by existing protocols, identify potential research directions and conclude. II. RELIABILITY IN WSN Reliability is the ability of the WSN to guarantee that the data is always delivered. The time the data is delivered is not a major concern but the data must always reach the intended recipient. Reliability in WSN is often dealt with in upper layers such as routing but we can also deal with it in the MAC layer by reducing packet loss [8].The following factors are the reasons why mechanisms to provide reliability are in place:  Constrained resources  Radio frequency interference  Synchronization The MAC layer has several methods to enforce reliability and the list below gives possible methods that can be used.