International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 A Reliable Routing Approach For In-Network Aggregation in Wireless Sensor Networks Subhashini.S#1 T. K Parani*2 # Student, M.E Communication Systems engineering, Anna University DSCE Coimbatore, India *Assistant professor, dept. Electronics &Communication Engineering DSCE Coimbatore, India Abstract— Wireless Sensor Networks are deployed densely in close proximity to the phenomenon to be monitored accurately in different applications. As these networks are highly populated, the data generated will be enormous. Since communication is the most expensive activity in terms of energy, Data aggregation technique should be made use of while transmitting data to the sink to save energy. With data fusion the size and number of packets transmitted can be reduced by aggregating the messages from sources in the intermediate nodes, thus decreasing communication cost, data traffic and energy consumption. For the network using data aggregation, the routing of data to the sink is an important and critical part in the processing, as the loss of aggregated data packets will have immense impact for data inference at the sink. Moreover, the routing technique used should be capable of reliable data transmission in all situations. In this paper, a novel data routing approach for in-network aggregation called DRINA (Data Routing for In-Network Aggregation) is proposed, that has the features such as reduced number of messages for setting up the routing tree, maximized number of overlapping routes, high aggregation rate and reliable data transmission even in the nodes failure situation. DRINA is compared with two other known methods: Information Fusionbased Role Assignment (InFRA) and Shortest Path Tree (SPT) algorithms using Network Simulator and is proved to be outperforming in all the evaluated scenarios. The future work will incorporate method to reduce the network overhead and to improve the aggregation rate. Keywords--- Wireless Sensor Networks, data aggregation, routing protocol I. INTRODUCTION Wireless Sensor Networks consist of large number of sensors which are deployed in the environment to monitor various phenomenons like pressure, temperature, sound, motion, or vibration in different locations. WSNs are widely used in many applications like monitoring critical infrastructure, home land security, environmental monitoring, communication, military and in many other critical applications[2]. ISSN: 2231-5381 Typically sensor is a battery operated device , thus are energy constrained. Node in a network performs basically three operations a) Sensing the event b) Processing the data and c) data communication. Energy consumption in a sensor node mainly depends on the amount of data gathered. So, the communication of data in the network is the most expensive activity in terms of energy consumed [7]. For this reason, all the protocols and techniques used in the WSNs should by considering the energy consumption in the sensors. WSNs are data-driven, where large amount of data generated has to be routed to the sink node, usually in a multihop fashion. In this scenario, routing technique plays a vital role in the data transmission process. A possible strategy to optimize the routing task is to use the available processing capacity provided by the intermediate sensor nodes along the routing paths. This is known as data-centric routing or innetwork data aggregation [1]. The resource utilization has to be minimized for the efficient data gathering in the networks. For this data aggregation has to be performed on the collected data in the nodes, which reduces the energy utilization in the nodes. Data aggregation forwards only smaller number of data, reducing the redundant data, leads to lower communication cost, energy saving and thus improves the lifetime of the network. The nodes forward the aggregated data packets to the sink node, where a lose in the packet cause severe impact in data analysis in the monitoring center. Routing algorithm used plays an important role in aggregated data forwarding and it should be capable of providing guaranteed service even in the case of node failure situations. For WSN, data aggregation aware routing protocol used should have some desirable characteristics such as: a reduced number of messages for setting up a routing tree, maximized number of overlapping routes, high aggregation rate, and also a reliable data transmission[1]. Here, a novel approach for data routing called Data Routing For InNetwork Aggregation (DRINA) is proposed. Our proposed method can maximize the data aggregation along communication route in reliable way, through a faulttolerant routing mechanism. http://www.ijettjournal.org Page 133 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 II CONVENTIONAL PROTOCOLS Various protocols are available for the data aggregation while forwarding the packets. They are mainly classified as tree-based approach, cluster-based approach and structure-less approach. A. Shortest Path Tree (SPT) Algorithm. It is a tree-based routing approach. It usually depends on hierarchical organization of the nodes. It uses a very simple strategy to construct the tree structure. Each source sends its information to the sink along the shortest path between the two[7]. Where these paths overlap for different sources, they are combined to form the aggregation tree. It has static routes[1]. B. Greedy Incremental Tree (GIT) Algorithm. It is also a tree-based approach. It is based on Direct Diffusion Approach. It establishes an energyefficient path and greedily attaches other sources onto the established path. The information is routed using the shortest path in the tree. Whenever a new branch is created new aggregation point is also selected. Routing tree cost is more[7]. C. Tiny AGgregation (TAG) Service. packets for aggregation. It has mechanisms for increasing the chance of packets meeting at the same node (spatial aggregation) and at the same time (temporal aggregation).It does not guarantee aggregation of all packets, the cost of transmitting packets with no aggregation increases in larger networks[7]. III ENERGY EFFICIENT ROUTING: DRINA The DRINA algorithm is also a cluster-based approach. In our algorithm, for each new event, it is performed the clustering of the nodes that detected the same event as well as the election of the clusterhead. After that, routes are created by selecting nodes in the shortest path, to the nearest node that is part of an existing routing infrastructure, where this node will be an aggregation point. Our DRINA routing infrastructure tends to maximize the aggregation points and to use fewer control packets to build the routing tree. Also, differently from the InFRA algorithm, DRINA does not flood a message to the whole network whenever a new event occurs. The main goal of our proposed the DRINA algorithm is to build a routing tree with the shortest paths that connect all source nodes to the sink while maximizing data aggregation. The proposed algorithm considers the following roles in the routing infrastructure creation: In the TAG algorithm, parents notify their children about the waiting time for gathering all the data before transmitting it so the sleeping schedule of the nodes can be adjusted accordingly. It makes use of shortest path to route the message[7]. It requires large number of message exchange to construct and maintain a tree. · D. Information Fusion-based Role Assignment (InFRA) Algorithm. · It is a cluster-based approach. The algorithm aims at building the shortest path tree that maximizes information fusion. Thus, once clusters are formed, cluster-heads choose the shortest path to the sink node that also maximizes information fusion by using the aggregated coordinators distance. For each new event that arises in the network, the information about the event must be flooded throughout the network to inform other nodes about its occurrence and to update the aggregated coordinators-distance[1]. This increases the communication cost of the algorithm and, thus, limits its scalability. E. Data-Aware AnyCast (DAA) Algorithm. · · Collaborator: A node that detects an event and reports the gathered data to a coordinator node. Coordinator: A node that also detects an event and is responsible for gathering all the gathered data sent by collaborator nodes, aggregating them and sending the result toward the sink node. Sink: A node interested in receiving data from a set of coordinator and collaborator nodes. Relay: A node that forwards data toward the sink. IV MODULE DESCRIPTION The DRINA algorithm can be divided into three phases. In Phase 1, the hop tree from the sensor nodes to the sink node is built. In this phase, the sink node starts building the hop tree that will be used by Coordinators for data forwarding purposes. Phase 2 consists of cluster formation and cluster-head election among the nodes that detected the occurrence of a new event in the network. Finally, Phase 3 is responsible for both setting up a new route for the reliable delivering of packets and updating the hop tree. It is a structure-less approach. Uses anycast to forward packets to one-hop neighbors that have ISSN: 2231-5381 http://www.ijettjournal.org Page 134 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 F. Hop Tree Building Flowchart for this phase is given in Fig 1. In this phase, the distance from the sink to each node is computed in hops. This phase is started by the sink node sending, by means of a flooding, the Hop Configuration Message (HCM) to all network nodes. The HCM message contains two fields: ID and HTT, where ID is node identifier that started or retransmitted the HCM message and HTT is the distance, in hops, by which an HCM message has passed. HTT in the HCM message is less than the value of HTT that it has stored and if the value of FirstSending(FS) is true. If that condition is true then the node updates the value of the NextHop variable with the value of the field ID of message HCM, as well as the value of the HTT variable, and the values in the fields ID and HTT of the HCM message. The node also relays the HCM message. Otherwise, if that condition is false, which means that the node already received the HCM by a shorter distance, then the node discards the received HCM message. The above steps are repeated until the whole network is covered. The flow diagram is shown below. Before the first event takes place, there is no established route and the HTT variable stores the smallest distance to the sink. On the first event occurrence, HTT will still be the smallest distance; however, a new route will be established. After the first event, the HTT stores the smaller of two values: the distance to the sink or the distance to the closest already established route. G. Cluster Formation and Cluster Head Election Fig 1 Flowchart for Hop Tree Configuration in the network. The HTT value is started with value 1 at the sink, which forwards it to its neighbors (at the beginning, all nodes set the HTT as infinity). Each node, upon receiving the message HCM, verifies if the value of ISSN: 2231-5381 Fig 2 Flowchart for cluster formation and leader election process http://www.ijettjournal.org Page 135 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 Fig 2 shows the process of cluster formation and the leader election from a cluster in the network. When an event is detected by one or more nodes, the leader election algorithm starts and sensing nodes will be running for leadership (group coordinator); this process is described in this phase. For this election, all sensing nodes are eligible. If this is the first event, the leader node will be the one that is closest to the sink node. Otherwise, the leader will be the node that is closest to an already established route. In the case of a tie, i.e., two or more concurrent nodes have the same distance in hops to the sink (or to an established route), the node with the smallest ID maintains eligibility[1]. At the end of the election algorithm only one node in the group will be declared as the leader (Coordinator). The remaining nodes that detected the same event will be the Collaborators. The Coordinator gathers the information collected by the Collaborators and sends them to the sink. A key advantage of this algorithm is that all of the information gathered by the nodes sensing the same event will be aggregated at a single node (the Coordinator), which is more efficient than other aggregation mechanisms (e.g., opportunistic aggregation). H. Route Formation and Hop Tree Update. Fig 3 shows the process of route update in the network. The elected group leader, starts establishing the new route for the event dissemination. This process is described in this phase. For that, the Coordinator sends a route establishment message to its NextHop node. When the NextHop node receives a route establishment message, it retransmits the message to its NextHop and starts the hop tree updating process. These steps are repeated until either the sink is reached or a node that is part of an already established route is found. The routes are created by choosing the best neighbor at each hop. The process of data transmission is described in this phase. While the node has data to transmit, it verifies whether it has more than one descendant that relays its data. If it is the case, it waits for a period of time and aggregates all data received and sends the aggregated data to its NextHop. Otherwise, it forwards the data to its NextHop. For every packet transmission with aggregated data, the Route Repair Mechanism is also executed. A route repair mechanism is used to send information in a reliable way. Sender nodes wait a predefined time period to receive a packet delivery confirmation. When the confirmation is not received by the sender node, a new destination node is selected and the message is retransmitted by that node[1]. ISSN: 2231-5381 Fig 3 Flowchart for Route Establishment. http://www.ijettjournal.org Page 136 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 evaluated in various scenarios to find the algorithm’s efficiency and its working capabilities in various situations.It are simulated by using NS-2 simulator version 2.34. Various performance parameters are evaluated. Data Packet Delivery Rate: Number of packets that reach the sink node. This metric indicates the quality of the routing tree built by the algorithms—the lower the packet delivery rate, the greater the aggregation rate of the built tree. Control Packet Overhead: Number of control messages used to build the routing tree including the overhead to both create the clusters and set up all the routing parameters for each algorithm. Efficiency: Packets per processed data. It is the rate between the total packets transmitted (data and control packets) and the number of data received by the sink. Routing Tree Cost: Total number of edges in the routing tree structure built by the algorithm gives the routing tree cost required. Loss of Aggregated Data: Number of aggregated data packets lost during the routing. In this metric, if a packet contains X aggregated packets and if this packet is lost, it is accounted the loss of X packets. Number of Transmissions: Sum of control overhead and data transmissions, i.e., the total packets transmitted by the nodes in the network. J. Simulation Parameters Table 1 simulation parameters Fig 4 Flowchart for Reliable data routing in the network. I. Route Repair Mechanism The route used by the algorithm is unique for data transmission, which maximizes the data aggregation along with the overlapping routes. Any failure in one of its nodes will cause disruption, preventing the delivery of several gathered event data. In the conventional methods, flooding of the message is used for identifying the failure nodes. In our proposed method, ACK based repair mechanism is used to identify the node failure. When a node sends aggregated data packet to its NextHop, the receiver node should transmit an ACK to its sender. If the receiver does not receive the ACK, it has to find an alternate NextHop to forward the packet. Thus a new route will be established excluding the repaired node. This ensures the reliable data routing in the network. VI PERFORMANCE ANALYSIS To evaluate the performance of DRINA, it is compared with some other known solutions such as InFRA and SPT. This two were chosen as they have same goal as that of DRINA algorithm in data routing. Performance is ISSN: 2231-5381 Simulation Parameter Simulator Topology Size Number of Nodes Communication Radius(m) # of events Event Duration (hours) Loss Probability (%) Simulation Duration (hours) Notification Interval (sec) Value NS-2(v2.34) 700 m 700 m 500 80 m 3 4 0 4 60 VII RESULTS Each of the discussed performance metrics of the DRINA algorithm are evaluated under various situations in the network for determining its efficiency. The algorithms performance is compared with the known http://www.ijettjournal.org Page 137 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 protocols SPT and InFRA under various criteria to out show its capability in various scenarios. Following parameters are varied for the performance evaluation and comparisons are, Network size. Number of Events Events Duration Communication Failure K. Impact Of Network Size The performances of the assessed algorithms are evaluated on the basis of number of nodes in the network, to evaluate the algorithms scalability. Fig 6 Overhead- Packets Vs Number of Nodes Fig 5 Data packets –Packets Vs Number of Nodes DRINA sends less than 75 percent of the data packets sent by InFRA and about 60 percent of the data packets sent by SPT. This result clearly indicates that DRINA maintains the quality of the routing tree even when the number of nodes increases. The data packets generated increases with the increase in the number of nodes. The graph shown in the Fig 5 indicates that DRINA has high aggregation rate compared to that of the SPT and InFRA algorithms. The data packets generated by the SPT are more than the InFRA, which has as medium delivery rate and aggregation rate. This shows that as the number of overlapping routes increases the data packets generated for transmission get decreased as the aggregation rate increases. DRINA is more scalable than the InFRA algorithm since our algorithm needs 30 percent less control messages to build the routing structure. On the other hand, the DRINA algorithm requires, on average, 25 percent more control messages than the SPT algorithm. However, the routing trees built by SPT results in 30 percent less efficiency than the trees built by DRINA algorithm. From the Fig 6, it is clear that the overhead transmitted over the network get increased with increase in number of nodes. The overhead for SPT is less when the number of nodes in the network is varied. The InFRA has maximum overhead in the network. As, overhead decreases the performance of the system, it is to be controlled. From the graph in Fig 7, it is clear that the efficiency of DRINA increases with the increase in the network size. The packets per processed data are less for DRINA when compared with that of SPT and InFRA algorithms. It proves that DRINA has high aggregation points in the network. Fig 7 Efficiency –Packets per processed data Vs Number of Nodes. DRINA is more than 20 and 28 percent efficient than the InFRA and SPT algorithms, respectively. This occurs because the DRINA algorithm needs less control ISSN: 2231-5381 http://www.ijettjournal.org Page 138 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 messages to build the routing tree when compared to InFRA. packets sent by the InFRA and SPT respectively. This indicates that one of the main advantages of the DRINA: by varying the number of events, DRINA builds routing trees more likely to have higher data aggregation rates. Fig 8 Tree Cost- Edges Vs Number of Nodes From the above result it is clear that the number of edges required to build the routing tree is less when compared to InFRA and SPT. So, the tree cost required is also less. Moreover, the routing tree built by DRINA has a better data aggregation quality than InFRA and SPT. L. Impact Of Number of Events The number of events was varied to evaluate the behavior of the proposed algorithms in networks with 1 to 6 events occurring simultaneously. Fig 10 Overhead– Packets Vs Number of Events The above graph indicates that DRINA needs less than 50 percent of the control messages requierd by the InFRA in the occurrence of events. The overhead of the DRINA is medium when compared to others. Fig 11 Efficiency – Packets per processed data Vs Number of Events Fig 9 Data Packets – Packets Vs Number of Events From the above graph it’s clear that DRINA sends fewer packets than the InFRA and SPT algorithms. For instance, DRINA sends approximately 81 and 67 percent of the data ISSN: 2231-5381 For more than one event, DRINA is more efficient than SPT and InFRA. http://www.ijettjournal.org Page 139 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 sent by InFRA and SPT, respectively. This indicates that by varying the time of an event duration, DRINA obtains a data aggregation rate greater than InFRA and SPT. Fig 12 Tree Cost– Edges Vs Number of Events The cost of the routing tree built by DRINA is less than 10 percent smaller than in the InFRA algorithm, and 30 percent smaller than in the SPT. The number of relay nodes required to transmit the data from source to sink node is less for DRINA when compared to that of the SPT and InFRA algorithms. Moreover, it generates better routing tree for the data transmission, which reduces the tree cost of the network. J. Impact Of the Event Duration The event duration is varied from 1 to 5 hours to evaluate the performance. The Fig 13 shows the data packets transmitted with increase in the event duration for the assessed algorithms. When the event duration is increased, the data packets transmitted by the DRINA is less when compared to SPT and InFRA. Thus, it indicates, the aggregation rate of the DRINA is better than the other algorithms. Fig 14 Overhead– Packets Vs Event Duration The graph in Fig 14 shows that DRINA requires less control messages to create the routing structure than InFRA but it requires more control messages than the SPT algorithm. Although DRINA requires 35 percent more control messages than SPT, SPT does not build a good data aggregation routing tree, as shown in previous results. It is clear that the overhead in the DRINA is medium when compared to the other two algorithms, which is to be controlled. Fig 15 Efficiency – Packets per processed data Vs Event Duration Fig 13 Data Packets – Packets Vs Event Duration DRINA algorithm sends less data packets than the other evaluated algorithms. More specifically, DRINA sends more than 84 and 64 percent of the data packets ISSN: 2231-5381 The above graph shows that DRINA is more efficient than InFRA and SPT. This algorithm outperforms the other evaluated algorithms even in scenarios of short-term events while InFRA exceeds the SPT only in scenarios where the event duration islonger (typically more than 2 hours). http://www.ijettjournal.org Page 140 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 aggregated data are retransmitted. On the other hand, SPT and InFRA protocols send less data packets when the communication failures probability increases. This happens because when a packet is lost due to communication failures the packets are not retransmitted and do not reach the sink. The Fig 18 shows the delivery rate of packets for the assessed algorithms with varying loss probability in the network. The graph shows that the delivery rate of the DRINA is high compared to that of SPT and InFRA algorithms as it make use of repair mechanism in the network. The delivery rate of SPT of very less compared to others as there is no efficient route repair technique used in the algorithm. Fig 16 Tree Cost– Edges Vs Event Duration K. Impact Of Communication Failures Communication failure is considered for evaluating the algorithms reliability. For this, the communication failure probability parameter is varied from 0 to 20 percent. The cost of DRINA path repair mechanism is also evaluated. The DRINA make use of route repair mechanism for the reliable data transmission in the network. The node failure in the network is identified by sending the ACK packet to the node in the transmission route. If found to be failure, then alternate route is used for transmission to sink. Thus with the failure node, reliable data transmission can be achieved in the network. The Fig 17 shows that the data packets generated is better for DRINA than the SPT and InFRA algorithms. Fig 18 Delivery rate of packets – delivery rate Vs Loss Probability With 20 percent communication failure, the delivery rate of InFRA is less than 30 percent, while DRINA delivers all aggregated data that have been sent. Therefore, the delivery rate of the aggregated data packets in DRINA is high when compared to other two algorithms. Fig 17 Data Packets- Packets Vs Loss probability In the DRINA algorithm, data packet transmission increases when the probability of communication failure increases. This is due to the fact that lost packets with ISSN: 2231-5381 Fig 19 Efficiency – Packets per processed data Vs Loss Probability http://www.ijettjournal.org Page 141 International Journal of Engineering Trends and Technology (IJETT) – Volume 7 Number 3- Jan 2014 From the above graph it’s clear that even in the loss probability scenario, the efficiency of the DRINA outperforms the other two algorithms. In summary, DRINA delivers aggregated data reliably with the best performance when compared to SPT and InFRA. VIII CONCLUSIONS Data Routing for In-Network Aggregation (DRINA) is efficient aggregation aware routing algorithms which play an efficient role in the event based WSNs. The routing mechanisms and the route repair mechanism followed by this algorithm supports reliable aggregated data transmission among the nodes. This algorithm is compared with other two known solutions namely SPT and InFRA extensively in various scenarios like varying the number of nodes, number of events, events duration, and loss probability for the communication cost, delivery efficiency, aggregation rate and data delivery rate. With the help of route repair mechanism and by increasing the number of aggregation points the DRINA outperforms in all the evaluated scenarios. It also has some key aspects required by WSNs aggregation aware routing algorithms such as a reduced number of messages for setting up a routing tree, maximized number of overlapping routes, high aggregation rate, and reliable data aggregation and transmission. Thus it is proved that the implementation of the DRINA in the networks can improve the lifetime of the network by reducing the energy consumption by transmitting relatively less number of packets to the sink. ACKNOWLEDGMENT I,SUBHASHINI S, student of M.E COMMUNICATION SYSTEMS, Dept. of ECE, Dhanalakshmi Srinivasan College of Engineering, Coimbatore. I would like to thank Asst. Prof. Ms.T.K..PARANI for her constant encouragement and support throughout the completion of the paper. I deeply express my gratitude to all the ECE department staffs for their valuable advice and co-operation. 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