A Fault Tolerant Protocol for Wireless Sensor Networks

Mohammad Mehdi Afsar

Department of Electrical, Computer and IT Engineering Qazvin Branch, Islamic Azad University

Qazvin, Iran M.Afsar@qiau.ac.ir

Mohammad Hossein Yaghmaee M. Associate Professor

Department of Computer Engineering Mashhad Branch, Islamic Azad University

Mashhad, Iran

Esmaeil Zeinali Kh. Assistant Professor

Department of Computer Engineering Azad University (QIAU)

Qazvin, Iran

Abstract—Today wireless sensor networks (WSNs) emerge as a revolution in all aspects of our life. WSNs have special specifications of themselves that made them different from other networks. Fault tolerance is one of the most significant of many challenges in these networks. In this paper, we present a cluster-based fault tolerant protocol that utilizes from energy efficient technique for clustering. We propose a novel mechanism for error detection. Our scheme detects faults and errors very accurately. Also, we propose a novel fault recovery technique to recover cluster-heads efficiently. Yet our scheme is accurate, saves energy of nodes too. That is very important for such networks.

Keywords- wireless sensor network; fault tolerance; cluster- head;

I. INTRODUCTION Wireless sensor networks (WSNs) have gained worldwide

attention in recent years, particularly with the proliferation in Micro-Electro-Mechanical Systems (MEMS) technology which has facilitated the development of smart sensors [1]. They are composed of a large number of tiny sensor nodes equipped with limited computing and communication capabilities. With networking these tiny nodes, we will reach to a smart environment.

WSNs have many widely applications such as military and medical monitoring, environment detecting and so on [1-4]. Most notable are those applications serving in harsh environments, such as coast and border protection, search-and-rescue and battlefield reconnaissance. By getting miniaturized sensors to operate unattended in such hostile setup, it would be possible to decrease the cost of the application and avoid the risk to human life as well. Since these nodes are tiny and limited-resources and prone to have faults, thus detect and recover faults via fault tolerant techniques is an essential issue in WSNs.

Yu et al. [5] have been divided the fault management process into three phases: fault detection, diagnosis, and recovery. As mentioned above, fault detection is first phase for fault management where a fault must be properly detected and then recovered with techniques. Thus fault detection is more

importance phase for providing an optimal fault tolerance in WSNs.

Several clustering techniques proposed in [6-7]. LEACH [6] (Low-Energy Adaptive Clustering Hierarchy) is an application specific data dissemination protocol that uses clustering to prolong the network lifetime. Must say, this proposal doesn’t consider energy level of candidate node and if lower energy node selected to CH, this node will die. In [7], a fully distributed clustering (HEED) algorithm has been proposed. Though, this algorithm considers residual energy to select some candidates’ CH, but spend energy more for communicate with CH.

Several fault detection and fault tolerant techniques have been proposed in [8-12]. In [8], a distributed fault detection algorithm has been proposed. This algorithm identifies faulty nodes based on comparison between neighbor nodes and dissemination of the decision made at each node. This way is a good scheme for scalable fault detection in WSNs, but doesn’t take energy consumption into account. In Sympathy [9] uses a message-flooding approach to pool event data and current states from nodes. This is a broadcasting mechanism with many communication messages. And this way doesn’t consider energy problem. In [10], algorithm is based on the idea that sensors from the same region should have similar values unless a node is at the boundary of the event-region. This algorithm works group-based. In [11], a fault-tolerant event boundary detection scheme has been proposed. Proposed scheme is a collaborative endorsement that designed to allow multiple nodes collectively endorsing a valid boundary claim for increased resilience against node compromise. Elhadef et al. [12] a distributed fault identification protocol was proposed. Dynamic-DSDP protocol is based on comparison approach and uses of self-diagnosis problem.

In [13], a cluster-based failure detection mechanism for wireless ad hoc network has been investigated. We know one of the most significant parameters of WSNs is energy consumption and inherent specifications of WSNs are different from ad hoc networks. WSNs are very power-constrained and such approaches that have been proposed for ad hoc networks may not be desired for WSNs. Several authors are inspired

2011 Seventh International Conference on Mobile Ad-hoc and Sensor Networks

978-0-7695-4610-0/11 $26.00 © 2011 IEEE

DOI 10.1109/MSN.2011.5

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2011 Seventh International Conference on Mobile Ad-hoc and Sensor Networks

978-0-7695-4610-0/11 $26.00 © 2011 IEEE

DOI 10.1109/MSN.2011.5

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2011 Seventh International Conference on Mobile Ad-hoc and Sensor Networks

978-0-7695-4610-0/11 $26.00 © 2011 IEEE

DOI 10.1109/MSN.2011.5

475

from this method and proposed some techniques [14]. ZFTMA [15] has been proposed with Zahid Khan et al. that is cluster-based fault tolerant management architecture. They divided whole network to four zones and a hierarchical management scheme proposed for this protocol. In this scheme, each zone has a manager and communicates with a central manager. Fault recovery has been proposed for cluster-heads too. This method is good scheme for hierarchical management, but using from resourceful device as ZM and his formation in some harsh environment is impossible. This specification made this method non-practical for such applications.

As mentioned above, in fault detection process, a tradeoff exists between accuracy and energy consumption. More schemes improve one, whereas lose other. Thus, in this paper, we use cluster structure for improve energy problem. Also, our proposed protocol detects and recovers faults and errors very accurately.

Rest of paper is organized as follows. Clustering technique is described in section II. The proposed fault tolerant protocol is described in section III. Section IV includes discussion and future work. Paper is concluded in section V.

II. CLUSTERING First, we describe an energy-efficient clustering technique

to whole network are fully connected. Clustering approach is a distributed scheme that it made network management process scalable. This approach helps us to have an energy efficient network by reduce communication messages to the sink or base station.

Clustering technique that we use for our scheme has two phases, that along this cluster-head (CH) is selected and also clusters have been formed. Here, we should point, we assume used WSN in our scheme is homogenous. In continuance, we explain these phases.

A. First phase_Cluster-head selection As discussed in [6], result shows that 5% of nodes in the

network operating as cluster-head can achieve good performance in a homogenous WSN with various parameter settings. In LEACH [6], an approach for CH selection has been proposed. Since this scheme does not consider remainder energy of nodes that select for CH, possible one node select for CH role and it’s remainder energy is insufficient and node will dead therefore whole network will disjoint. For this reason, we consider remainder level energy of nodes as follows.

In this phase, each sensor node generates a random number between 0 and 1, and if the number has been generated be less than the threshold T (n), then this node becomes the candidate CH as follows:

:11 ( mod )

0

( )

p if n Gp r

p

otherwise

T n∈

− ∗���= ����

(1)

After a node becomes the candidate CH by “(1)”, it checks its energy level. If energy level is greater than Ethr thus this node become CH, and if energy level is less than Ethr thus node doesn’t selected as CH. This consideration showed as “(2)”.

)( thr CH con conIf E E then CH CH

Else continue CH selection phase

−≤ =�����

(2)

Whereas CHcon is candidate CH and if remainder energy be greater than Ethr, this node is selected as CH.

B. Second phase_Cluster formation After a node was selected as a CH, then clusters has been

formed. In our scheme, we assume all nodes are similar. Thus nodes have same radius transmit and energy. After selection CHs, CHs broadcast a “CH-adv” packet. All ordinary nodes that receive this packet, must join to a CH where is in closely of this node. Each sensor node becomes a part of a cluster by choosing a CH that is closer to itself based on the received signal strength indicator (RSSI). This mechanism is as follow.

The ordinary node receive CH-adv packet. Thus sends a “CH-join” packet to CH that has highest RSSI. This packet contains ID and energy level of this node. CH receives this request and adds this node and its information to a table. This table includes ID and energy level of all nodes that are in this cluster. Hence clusters are formed and all nodes join to a special cluster.

Fig.1 shows the clustering operations. As showed in fig.1, CHs send “CH-adv” packet to ordinary nodes. After that, each ordinary node where receive this packet should recognized him to CH. For this mean, send a “CH-join” packet to CH and became a member of this cluster. In fact, CHs formed clusters based on received signal strength indicator (RSSI).

Figure 1. Clustering operations in WSNs.

Figure 2. Inter-Cluster communication in WSNs.

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In fig.1, Star nodes operate as gateway and usually famous as GW nodes. GW nodes send packet from a CH to other CH, and CHs by these nodes communicate with together. Also, rectangular nodes are CHs and circle nodes are ordinary nodes. In fig.2, an inter-cluster communication has been showed. Inter-cluster communication for some targets (e.g. CHs recovery, dissemination of faulty nodes information to whole network) is very important.

III. FAULT TOLERANT PROTOCOL In this section we describe our fault tolerant protocol. We

propose a novel protocol that detect and recover faults efficiently. Fault tolerance is the ability to ensure the functionality of the network in the events of faults and failures [15]. Proposed fault tolerant protocol includes two sections: fault detection and fault recovery. Our proposed protocol tolerates transient faults efficiently. Transient faults are caused by interferences and noises of external environment. In continue, we explain details of fault tolerant protocol.

A. Fault detection As discussed in [5], in fault management process, fault

detection is first phase and may is most important from other phases. However, faults should detect accurately and correctly. One issue is in fault tolerance specification of WSNs, existence of a tradeoff between accuracy and energy consumption. Hence we use cluster-based fault detection that saves energy of nodes and utilize a technique with high accuracy. Our fault detection process has follow levels:

1) Intra-cluster fault detection: If data from a node does not receive for a pre-defined periodic time, then CH waits for a period again. Because it is possible through interferences and noises data was lost, whereas node is healthy. After second period, if CH does not receive packet assumes this node is faulty. Therefore, CH broadcast a packet to all neighbor CHs and all nodes in his cluster and declares this node with this ID is faulty.

2) Intra-cluster error detection: When CH receives data from nodes that located in same location, computes a “median value” for these data and store in table. Each time data arrives, CH compares this data with “median value”. While difference is greater than a pre-defined constant deviation as “�”, CH detects an error and node that produced this data, is considered as faulty. Again, CH broadcasts a packet to all neighbor CHs and all nodes in his cluster and declares this node with this ID is faulty.

3) Inter-cluster fault detection: CHs are an important part of WSNs and their failure must detect immediately. For this reason, we use this approach. CHs send a packet to other CHs periodically. This packet contains information of all nodes that exist in cluster. If a CH doesn’t receive this packet from a neighbor CH, considers that as a faulty CH.

B. Fault recovery After a CH detect faulty neighbor CH, start recovery

operation as follow. CH looks at the table and selects a node with highest energy level. Then sends a packet “new-ch” to this

node, and this node starts cluster formation phase. Note that packet that send between CHs include all node’s data like as energy level, location, and ID.

This method cause CH’s failures are recovered efficiently. Because without interfere of sink or base station (BS), failure is detected and recovered. Hence this method reduces number of communication messages between BS and nodes, therefore, save the energy. As we know, most amount of energy spent for communications.

IV. DISCUSSION AND FUTURE WORK In this article, we present a fault tolerant protocol. This

protocol characterized by two specifications: clustering method and fault tolerance techniques. This protocol is energy efficient that this feature is essential for WSNs. Our proposed protocol detects faults and errors accurately, and recovered faults in convenient manner.

In our protocol, clusters are formed in two phases: CH selection phase and cluster formation phase. CH selection phase is based on LEACH [6] technique. Despite, we modify this scheme and include remainder energy of candidate nodes in CH selection. In cluster formation phase based on RSSI, clusters are formed. This clustering scheme maximizes lifetime of network. Additionally, this method increases scalability of management process of whole network. Clustering mechanism is a suitable hierarchical process.

Our proposed protocol provides fault tolerance specification as follow. First, protocol detects faults and errors. Fault detection achieved by exchange communication scheduled messages between nodes and CHs. Error detection achieved by a comparison mechanism. Our error detection is a novel mechanism. Second, protocol start a recovery phase for recovers CHs. This method is novel and operates in autonomous manner. Because protocol hasn’t need to communicate with BS/sink to decide how operate.

We are trying to investigate our protocol and simulating this via MATLAB simulator. MATLAB (matrix laboratory) is a numerical computing environment and fourth-generation programming language. Our scheme arise some challenges as computing constant deviation “�”, security in communication messages , and localization of CHs.

V. CONCLUSION Fault tolerance is a key feature of QoS design in WSNs. In

this paper, we proposed a cluster-based fault tolerant protocol that utilizes an energy efficient technique to formed clusters. After clusters are formed, our protocol detects faults and errors accurately. A novel error detection technique has been proposed in this paper. After that, protocol starts a new proposed recovery mechanism. In recovery phase, our scheme recovers cluster-heads (CHs) with an efficient technique without interfere of sink/BS. This method decreases communication messages between CHs and sinks/BSs, therefore works in autonomous mode.

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