International Conference on Methods and Models in Computer Science, 2009

A Flat Routing Protocol for Sensor Networks

Anita Kanavalli' Dennis Sserubiri/, P Deepa Shenoy', Venugopal K R4 and L M Patnaik'1,2,4 Department ojComp:ter Science and Engineering, University Visvesvaraya Col~ege ~jEngineerinF!Bangalore

5Vice Chancellor, Defence Institute ofAdvanced Technology (Deemed University), Pune Indiae-mail.i anita.kanavaltiiiigmail.com

Abstract-The way in which Wireless Sensor Networks(WSN) are designed requires that energy be taken as themost crucial element if WSNs are to be used in the mosteffective way to serve the purpose for which they havebeen deployed in the target region. Routing protocols arethe main aids that can assist in reducing the energyconsumption required by the transmission of datathroughout the sensor networks. In this paper we haveproposed a flat routing protocol for sensor networks. Thisapproach is one of the simplest protocols in terms of theroute determination process and the number of messagesthrough the network. Routes from the source to thedestination are determined by use of only the hop countand remaining energy of the neighbor nodes for each node.The proposed protocol is simulated and is compared withthe flood routing protocol.

Keywords- wireless sensor networks, source initiated,energy consumption, node life time, flat routing

I. INTRODUCTION

Ever since the emergence of wireless sensornetworks (WSNs) about two decades ago a lot of

research regarding routing protocols in WSNs has beendone. A wireless sensor network is a network of sensornodes deployed in urban or remote areas to monitor ongoing events as they happen. Wireless sensor networkcan be used for military, health, environmental,industrial purposes and so on. The sensor nodes can bedeployed in large numbers ranging from tens tothousands in the area of interest. These are usually small,inexpensive, low power sensors that can be deployedanywhere. Sensor nodes are meant to be self configuringhaving one or more embedded sensors, wirelesscommunication and data processing units. Sensor nodesare characterized by their limited supply ofenergy.

Due to the limited battery capabilities, sensor nodessuffer an energy resource constraint such that if therehappens to be a failure of even a single node, the wholenetwork topology changes requiring the network setupto be initiated again. This means that the life time of thenetwork greatly depends on the life time of theindividual nodes in the network of sensor nodes. Sincesensor nodes are deployed to monitor events happeningin a particular region, there is always a sink node or basestations to which the sensing nodes have to route thesensed data for processing. The main advantage of thesink node is its prolonged energy supply since it isalways accessible and therefore it always guaranteesthat if sensed data reaches the sink node, then the

probability of loosing the sensed data is reduced whichis not the case for the source nodes. Node failure can bedue to battery outage since sensor nodes are equippedwith a fixed source of battery power. An importantfactor that influences the consumption of more power inwireless sensor network is that each sensor nodeconsumes power not only for sensing but also forprocessing the sensed data and transmitting or receivingdata to or from its neighbors. These are the reasons forwhich the efficient use of power is the primary andperhaps the most important consideration for design~g

a wireless sensor network protocol [1]. Routmgprotocols in wireless sensor network are designed insuch a way that they keep the network life time for alonger period by efficiently utilizing the availableresources in the most economical way.

Routing in wireless sensor network is a challengingtask because of their characteristics that differentiatethem from other wireless networks. Usually the numberof nodes in the network is so high that it is not possibleto have a global addressing scheme as the overheadwould be very high to maintain. In WSNs, sometimesgetting the data is more important than knowing thenode identifiers (IDs) of the nodes that sent the data. Incontrast to typical communication networks, almost allapplications of sensor networks require the flow ofsensed data from multiple sources to a particular basestation. This however, does not prevent the flow of datato be in other forms like multicast or peer to peer. Thesensor nodes are tightly constrained in terms of energyprocessing, and storage capacities. Thus, they requirecareful resource management. In most applicationscenarios, nodes in wireless sensor networks aregenerally stationary after deployment except for a fewmobile nodes. A number of factors do influence thedesign of routing protocols for wireless sensor netw?rk.They are node deployment, energy consumption,scalability, data aggregation, coverage and connectivity.There exist a number of routing protocols classifiedaccording to network structure. They are hierarchicalrouting protocols, flat routing protocols and Locationbased routing protocols. In flat routing protocols, allnodes in the sensor network have equal roles ingathering information [2]. They all have the sameinformation about the state of the network. Some of theflat routing protocols that have been proposed include:Directed Diffusion, Spin, Rumor routing, Minimum Cost

Forwarding Algorithm, Gradient Based, Cougar, andAcquire. In this paper a flat routing protocol has beenproposed.Motivation: Proposing a new routing protocol forwireless sensor networks is one of the most challengingworks to accomplish successfully. Despite thechallenges, it is crucial that all important issues beaddressed in order to come up with the best results.Contribution: In this paper, a new flat routing protocolis proposed and simulated. The issues that are addressedare the calculations of the energy values using the radiomodel in [3] with regard to the distances between nodes.This is mainly due to the fact that when nodes aretransmitting data diagonally, more energy is used fortransmission and reception of messages than whentransmitting or receiving data from vertical or horizontalneighbors. In a uniform network, the nodes are able tocommunicate diagonally. Then the distance between thediagonal neighbors cannot be the same as those forhorizontal or vertical neighbors. It will always be muchlarger. Also during network maintenance, it is possiblethat nodes remove dead neighbors from their tableduring the energy updates process rather than wait forthe periodic network maintenance message.Organization: The rest of the paper is organized asfollows: Section II gives overview of related work. Themodel and the problem defmition, the analysis of thealgorithm is presented in section III. Theimplementation details and the performance analysis arediscussed in section IV. Section V contains theconclusion.

II. RELATED WORK

C Intanagonwiwat et al [4] proposed one of the mostpopular routing protocols for wireless sensor networkcalled directed diffusion. This is data centric andapplication aware routing protocol. All data generated isnamed with attribute-value pairs. Data that is on its wayto the sink is combined as it is forwarded in order toremove redundancy, minimizing the number oftransmissions thus saving battery energy which in turnprolongs the network life time. The performance of dataaggregation methods in directed diffusion methods isaffected by factors such as position of the source nodes,number of sources and the network topology [2].

SPIN is a family of adaptive flat routing protocolsthat were proposed by Heinzelman et al [5],and [6] thatuse a technique of data negotiation and resourceadaptive algorithms. These families of protocolsdisseminate information to each and every node in thenetwork with the assumption that all nodes in thewireless sensor network could be potential base sinks.This enables a user to request for information from anynode in the network and get the requested informationsince all the nodes in the network have the sameinformation. In these protocols all neighbor nodes havethe same data and it is only data that the others nodes donot have that distributed to the neighbor nodes.

Rumor routing [7] is intended to be used in areaswhere geographical routing cannot be used. It variesfrom directed diffusion in a sense that when the numberof events is small and the requests are large, the idea isto flood the events. Rather than flooding the entirenetwork with queries, the queries are routed to only thenodes that have observed events. In order to route eventsthrough the network, the rumor routing algorithmemploys long-lived packets, called agents. When a nodedetects an event, it adds such event to its local table,called events table, and generates an agent [2]. Theseagents eventually disseminate information to distantnodes about the state of local events. In rumor routing,if a node generates a request for an event, the othernodes which know the route may generate a response tothe request by inspecting their events table. Thiseliminates the need for flooding the whole network intum reduces communication costs. Tests show thatrumor routing is good at energy saving compared toflood routing.

In paper [8] the main objective is to increase thenetwork life time as its name suggests. Energy awarerouting is a destination initiated reactive routingprotocol that maintains a set of paths to the base station.This is a possible means of a probability value thatdepends on how low the energy consumption of eachnode can be attained. By choosing different paths atdifferent times, it is possible to conserve the energy ofthe individual nodes without depleting them quickly.Through localized flooding, it is possible to discover allroutes from source to destination and their costs.

SEER: A Simple Energy Efficient Routing Protocolfor Sensor Networks [9] was proposed by Gerhard P.Hancke, C. Jaco Leuschner as an energy efficientrouting protocol for sensor networks. It is a flat routingprotocol that achieves energy efficiency by use of hopcount, remaining energy in the nodes and routingdecisions are based on the distance to the base station.These metrics are used to determine the routes forforwarding data to the sink. It is a source initiatedrouting protocol and it uses a uniform network toachieve this efficiency. The authors of this protocolclaim that if the sink node it at the center of the networkwith the source nodes uniformly distributed from thesink and from each other, it is possible that significantenergy efficiency can be achieved.

III. MODEL AND ALGORITHM

A. Radio Model

There is a great deal of research in the area of low­energy radios. The assumptions about the energydissipation in the transmit and receive modes, willchange the advantages of different protocols. Theproposed protocol operation uses Heinzelman et al [2]radio model for the energy consumptions of themessages. We assume that radio dissipates nJ/bit to runthe transmitter and the receiver circuit and energy isdissipated by the transmitter amplifier. We also assume

that there is an energy loss due to channel transmission.According to this radio model the energy required forthe transmission and reception of the messages is givenby the following equations.

E Tx = E Elec .k + & amp .k.d2where, E Tx is the

energy required for the transmission of the messages.

E Rx = E Elec.k where, E Rx is energy required for

reception of messages, and E Elec is the energy

consumed by the transceiver electronics, k is the size of

the message in bits, eamp is the energy consumed by

the transmitter amplifier and d is the transmissiondistance in meters. For these parameter values,transmitting and receiving a message is not a low costoperation. Thus the protocol should reduce the transmitdistances and also the number of transmit and receiveoperations for each message. The radio channel issymmetric such that the energy required to transmit amessage from node A to node B is the same as theenergy required to transmit a message from node B tonode A. All sensors are sensing the environment at afixed rate and thus always have data to send to the end­user.

B. Problem definition

The protocol requires five steps for its operation.• Network setup and neighbor discovery• Transmitting new data• Forwarding data• Energy updates• Network maintenance.The issues that are addressed are the calculation of

energies made using the radio model in [11] with regardto the distances between nodes and removal of deadnodes from the neighbor table.

During network maintenance, it is possible that nodesremove dead neighbors from their table during theenergy updates process rather than wait for the periodicnetwork maintenance message.

c. Algorithm

The algorithm for the proposed protocol is explained inthis section1. In the network setup and neighbor discovery, the sinknode broadcasts a network setup message to itsneighbors which in turn forward it to other neighboringnodes. This message contains network setup informationthat will be updated as the message is forwarded. Theinformation includes the hop count and energy, whichchange as the message is forwarded further each nodestoring this information about its neighbor andforwarding it.2. During the transmission of new data, if a node hasinformation to be transmitted, the node checks in itsrouting table for the best neighbor that is close to thesink based on the hop count and energy of the node.This is done starting with the hop count and then the

energy depending on whether the node has more thanone node in its neighbor table with the same hop countand then which has the highest energy remaining.3. During the data forwarding process, the same processfor neighbor node selection is done except that thecreator node cannot be selected this time during theneighbor selection process. When the node's remainingenergy falls below a certain threshold, the nodetransmits an energy update message to its neighborsinforming them about its energy status. When the nodesreceive the energy message, they remove the node thatsent the message from their neighbor table.4. During the network maintenance, the sinkperiodically sends a network maintenance messages forthe nodes to add new neighbors that have joined thenetwork.

D. The Mathematical model

1. The distances between the nodes are assumed to beuniform including the diagonal neighbors of the nodes.This is not the case during the calculation of thedistances of the diagonal members, Pythagoras theoremis used in order to determine the distance in the energycalculation of the power dissipated in transmission andthe reception of the messages. Taking uniform distanceswill yield wrong results as the distance from the sourceto the next diagonal neighbor increases. Though duringthe protocol operation, it is indicated that the neighborshave to be a meter apart. Assuming the distances aremore than a meter a part, then the diagonal distanceswill be much bigger.

It is possible that the distances be calculated using thechannel node Free Space Loss Model:

p = ~r (4Jr)2 *d 2

Awhere P, is the received power, P, the transmitted

power, A is the wavelength of the signal and d is thedistance between sender and receiver.2. During the network maintenance step, it is mentionedthat the sink sends a network maintenance message forthe nodes to remove neighbors that have failed. Thisprocess can be done during the energy update step whennodes transmit energy update messages to their neighbor.This reduces the amount of energy that will be usedduring the storage of information for failed nodes. Thereception and the transmission energy is computed using

the radio model formula in section III A where E Elec =

50nJ/bit and camp is 100pJ/bit. Node energy is reduced

by for Reception and Transmission ofmessages.

IV. IMPLEMENTATION AND PERFORMANCEANALYSIS

A. Implementation

OMNET [14] is a discrete event simulator uses bothnetwork description language and C++ to defme all theobjects in the simulation. In this case objects included

things such as the messages and nodes. The messagesare defmed with the various necessary fields for thenetwork layer. The proposed algorithm was defmedusing C and inbuilt functions of OMNET. The nodedetails are as follows. Before the network and neighbordiscovery process, node were assigned initial parameterswhich included

• Node address• Initial energy = 5mJ• Minimum energy = 0.00475J• Hop count = 0

The neighbor table entry in each node had theinformation of address, energy and hop count. There arethree types of messages used in the simulation.1. The network setup and neighbor discovery message,the parameters included are source address, destinationaddress, hop count, energy level of sender node and thesequence number.2. Data message, the parameters included are sourceaddress, destination address, creator address, energylevel ofsender, payload, and hop count.3. Energy message, the parameters included are sourceaddress, destination address, energy level, and hopcount

The network setup and neighbor discovery messagewas set to 64bits, data message was setup to 105 bitsand energy message to 56 bits. The first message to besent through the network is the network and neighbordiscovery message broadcast by the sink node. As themessage is routed through out the network, nodes keptupdating their neighbor tables to include newlydiscovered neighbors that are directly connected to themand also node parameters, i.e. the hop count of the node,energy were updated to reflect the reduction in energy,hop count and address read from the received networksetup and neighbor discovery message. Nodes alsoupdated their node parameters to reflect their reductionin initial energy and hop count. As each node receivedthis message, node parameters were updated andmessages parameters where changed before forwardingthe message to the next neighbor. After all the nodes inthe networks had updated their parameters, then a datamessages is generated.

Generated data messages which are generated bynodes are routed through the networks following thealgorithm in section IV A. Also the node energy of thenode that generated a data message is updated to reflectthe reduction in energy before sending out the messagesand neighbor table energy for the node selected as theforwarding node was updated in the neighbor table.Only the creator address did not change until themessage was received the sink node. If the node'senergy got below the set minimum energy, then thismessage broadcast out a message to its neighbors toinform them of its status. Every node that received thismessage removed this node from it neighbor table sinceit has failed. The algorithm for the neighbor selectionexplained here below.1. If neighbors hop count < own hop count2. If there is only one such neighbor go to 3 else go to 4

3. Select neighbor if energy is above predefinedthreshold, go to 5

4. Select neighbor with highest remaining energy5. Update neighbors remaining energy table6. Send the message and end7. If neighbors hop count = own hop count go to step 28. Discard the message and end

We have implemented flood routing protocol and theproposed protocol in OMNET.

B. Simulation Setup

The simulation setup was a network of 49 nodesuniformly distributed which were equidistant from eachother. Each node had an address which was its index inthe array of nodes and parameters for energy, sequencenumber and the address. The figure 1 shows the nodesetup in OMNET considered for the simulation of boththe protocols.

Step one of implementing the proposed protocol is,setting up the network as a uniform network with thesink node being in the center. The simulation beginswith the broadcast message sent by the sink node tosetup the network by updating the hop count, addressand energy levels of each node in the network. Eachnode stores the details of each of its 8 neighbors. Aseach node receives the broadcast message, it reads thehop count of the sender and energy level of the sender,stores these values in its neighbor table for that senderthat sent the message and then changes the sourceaddress to its own and energy, increments the hop countand then forwards the broadcast message.

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I. .1. ;.;:. J..;. 1': l.,!.

~r! , L!

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Fig. 1: The nodes consideredfor the simulation

Before sending the message, the node reduces itsenergy by the number of messages it received and thenumber of messages it sent out. After the network hasbeen successfully setup with each node having up todate information of its neighbors and its own parameters,then a data message is generated by any node in thenetwork. For each data message, the creator node willreduce its own energy as the energy is spent intransmission, and then sends out the message with itsown source address, creator address and energy level.The selected neighbor's energy will have to be updatedin the source node before sending out the data message.When a node receives the data messages, it reads thesource node address, updates its energy value in itsneighbor table, reduces its own energy by the ReceptionEnergy value, and repeats the same procedure as thesource node for selecting neighbor according to theneighbor selection algorithm as explained in theprevious section. Then the node forwards the message.

TABLE I ENERGY CONSUMPTION BY NODES

Fig. 2: No. of Messages Vs Single Node Failure

Single Node Failure

messages, while for the proposed protocol the energy is0.00491596J for 8 data messages.

REFERENCES

[I] F. Zabin, S. Misra, 1.Woungang, H.F. Rashvand, N.-W. Ma, M.Ahsan Ali, "REEP: data-centric, energy-efficient and reliablerouting protocol for wireless sensor networks", lETCommunications, 2008, Vol. 2, No.8, pp. 995-1008

[2] Jamal N. AI-Karaki, Ahmed E. Kamal, "Routing Techniques inWireless Sensor Networks: A Survey", Dept. of Electrical andComputer Engineering, Iowa State University, Ames, Iowa500Il

[3] W. Heinzelman, A. Chandrakasan and H. Balakrishnan."Energy-Efficient Communication Protocol for WirelessMicrosensor Networks", Proceedings of the 33rd HawaiiInternational Conference on System Sciences (HICSS), pp. 1-10.4-7 January 2000.

[4] Intanagonwiwat, C., Govindan, R. & Estrin,D, " Directeddiffusion for wireless sensor networks.", lEEE/ACMTransactions Networking, Vol 11., (2003) 2-16

[5] W. Heinzelman, 1. Kulik, and H. Balakrishnan, "AdaptiveProtocols for Information Dissemination in Wireless SensorNetworks", Proc. 5th ACM/lEEE Mobicom Conference(MobiCom '99), Seattle, WA, August, 1999. pp. 174-85.

[6] 1. Kulik, W. R. Heinzelman, and H. Balakrishnan, "Negotiation­based protocols for disseminating information in wireless sensornetworks", Wireless Networks, Volume: 8, pp. 169-185,2002.

[7] Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, "Asurvey on sensor networks", IEEE Communications Magazine,Volume: 40 Issue: 8, pp.l02-114, August 2002.

[8] R. C. Shah and 1. Rabaey, "Energy Aware Routing for LowEnergy Ad Hoc Sensor Networks", IEEE WirelessCommunications and Networking Conference (WCNC), March17-21,2002, Orlando, FL.

[9] Gerhard P. Hancke, C. Jaco Leuschner. 'SEER: A SimpleEnergy Efficient Routing Protocol for Wireless SensorNetworks", Department of Electrical and Computer Engineering,University of Pretoria, Lynnwood Road, Pretoria,0002.Reviewed Article--SACJ No. 39, 2007

[10] F. Ye, A. Chen, S. Liu, L. Zhang, "A scalable solution tominimum cost forwarding in large sensor networks",Proceedings of the tenth International Conference on ComputerCommunications and Networks (lCCCN), pp. 304-309,2001.

[Il] C. Schurgers and M.B. Srivastava, "Energy efficient routing inwireless sensor networks", MILCOM Proceedings onCommunications for Network-Centric Operations: Creating theInformation Force, McLean, VA, 2001.

[12] Y. Yao and J. Gehrke, 'T he cougar approach to in-network queryprocessing in sensor networks", SIGMOD Record, September2002.

[13] N. Sadagopan et al., 'T he ACQUIRE mechanism for efficientquerying in sensor networks" , Proceedings of theFirstlnternational Workshop on Sensor Network Protocol andApplications, Anchorage, Alaska, May 2003.

[14] OMNeTT++ "Discreet Event Simulation System"http://omnetpp.org/

V. CONCLUSION

It can be therefore realized that a new flat routingprotocol for sensor networks that performs far muchbetter than flood routing protocol. This can bevisualized in the two graphs. This is evidenced both inthe failure of nodes and the average remaining energy ofnodes after transmitting data messages in the network.The results confirm that the proposed protocol scaleswell and improves network lifetime by limiting thenumber of messages that are sent through the network.Overall, the proposed flat routing protocol achieves avery high level of energy efficiency.

Proposed

ProposedProtocol

FlooRouting

Fig. 3: Average remaining energy for nodes

Flood Routing

50 1------- - - - - - - - -,__---,__----14a 1------- - - - - - - - 1

~ a 1------- - - - - - - - 1

~a+---------j15+-- -1

I0t==~~;.======L_J==ja

Energy Consumption in joules

Flood min avg energy 0.004878535Routing

max ava energy 0.005Proposed min avz enerzv 0.00491596Protocol

max avg energy 0.005

0.00500.00

0.00490.004

0.00480.004

It is realized that the average remaining energy in thenetwork after sending out data messages was higher inthe proposed protocol as compared to flood routing asshown in figure 3 above. In flood routing, the averageremaining energy is 0.004878535J for only 2 data

The data message will eventually reach the sink node.When a nodes' energy fall below a certain threshold, inthis case 0.0475J, the node will broadcast an energyupdate message. The node will reduce its own energy bythe transmission energy value. The minimum energywas set to 0.0475J. Any other messages received will bediscarded by that node that is out ofenergy.

C. Results

I. It is realized that flood routing required only 2 datamessages to be sent through the network for a singlenode failure while for the proposed protocol it was 45messages sent in a network of 49 nodes . This is asshown in the fi ure 2.

Energy Consumption ini()lI) p c;;:

2. The average energy in the network of 49 nodes ismeasured for the proposed protocol after sending 8messages and also for the flood routing protocol aftersending only 2 messages. The Minimum and theMaximum average energy consumption by the networkof49 nodes is shown in table I.