Multicast Routing Protocols in Wireless Sensor Networks (WSNs)

7/31/2019 Multicast Routing Protocols in Wireless Sensor Networks (WSNs)

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Multicast Routing Protocols in WirelessSensor Networks (WSNs)M. A. Khan, M. Ahsan, G. A. Shah, Muhammad Sher

Abstract

Wireless sensor network (WSN) is formed by collaboration of sensor nodes and static sink nodes. The sensor nodes sense cer-

tain information about an event from its environment and forward them to a sink node for processing and analysis. Besides

unicast routing to a single sink node, a wide variety of WSN applications have also realized the presence of multiple sinks that

necessitates multicast routing for efficient data dissemination to multiple destinations. For example, in emergency scenarios

such as fire handling or any disaster surveillance, it isgenerally required to report event information to multiple sinks that in-

cludes hospitals, ambulatory service, rescue cell etc.However there are certain challenges in multicast routing protocols such as

nodes mobility, energy and bandwidth constraints which need to be addressed. Various multicast routing protocols have been

proposed by many researchers. This survey contributes in providing a comprehensive understanding of these multicast routing

protocols, and identifies the future research directions in multicasting. We provide a detail survey of the existing multicast rout-

ing protocols and identify different issues and challenges that need to be resolved. Conclusion derived in this paper can lead to

a new paradigm of multicast routing in Wireless Sensor Networks (WSNs).

Index Terms Wireless Senor Networks (WSNs), Priced Trackand Transmit (PTNT), Branch Aggregation Multicast (BAM),Geographic Multicast Protocol (GMR), Hierarchical Rendezvous Point base multicast (HRPM).

1 INTRODUCTION

IRELESS sensor network (WSNs) is a collection ofdifferent sensor nodes which sense certain infor-

mation from its surrounding and transfer that infor-mation for further processing to one or more interestednodes called sinks. A number of WSN applications areemerged to observe an abnormal activity in the sensorsdeployment area, such as military movement in a battle-field, sensing environmental changes and health monitor-ing. In some applications, sending the state informationonly to a single node is not sufficient such as bomb blast,earthquake, etc. Therefore, it is imperative to report to agroup of nodes about the sensed events/data [1]. Due toresource limitations, sensor nodes usually adopt multi-hop communication paradigm in which packets arepassed to the destination through multiple intermediatenodes. In unicast routing model, a source has to maintainindependent routing paths with each of the destinationnodes. This consumes tremendous amount of resources in

maintaining these paths and routing event information.This problem can be addressed using a carefully designedmulticast routing protocol. A number of routing tech-niques based on tree, mesh, or geographical zone topolo-gy are proposed for wireless sensor networks. Theseprotocolscan be classified into unicast, geocast, anycast,broadcast andmulticast routing protocols. Unicast routingprotocols are usedto send sensed information to a singlenode at destination. Geocast routing protocols are usedto deliver sensed data toone or more nodes lying in a spe-cific area of the network and there are geographical re-strictions in these protocols rather than specific node ID.

Anycast routing protocols deals with data delivery to anynode in a particular network. Broadcast routing protocolsare used to send sensed data from a source sensor node toall other nodes lying in the deployment field.While mul-ticast routing protocols are used for sending data packetsfrom a single source to a group of nodes. The choice ofany of these data dissemination techniques depend on theobjectives of the application or certain scenario. Multicastrouting protocols have become very important in emer-gency handling applications since these protocols mini-mize energy and bandwidth consumption, when thereare multiple dispersed destination nodes. Consider a firemonitoring network in which sensor nodes are deployedin a building to detect the possibilityof fire. If the buildingcatches fire at some point, then the sensor nodes at thatlocation sense some smoke or abrupt temperature raise.The sensed information might be sent to anumber ofnearby sensors at other parts of the building to adjusttheir sampling rate in addition to one or more sinks offire

responders such as fire brigade office, ambulance service,hospitals etc. Hence, reporting emergency information toa group of sensor nodes besides the sink, allow the firerescue teams to start their operations in time and moreeffectively. Thus, it is imperative to support multicastrouting when eventdata needs to be disseminated to agroup of nodes [2]. Push and Pull are the two basic datadissemination models insensor networks to gather eventinformation. In push approach, all the sensor nodes in thenetwork sense event and report to sink nodes withoutany explicit request. This model is not suitable for appli-cations when events happen frequently and temporally

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correlated. In such a case, pull model is more appropriatein which this information is pulled when required by ex-plicitly sending query in network [3]. On the other hand ahybrid push pull approach is also proposed in which sen-sor nodes store data at a few relay points and then sinkpulls data from these intermediate nodes [4].

Multicast routing protocols usually follow Pulldata dissemination mode land inherits the issues associ-ated with it such as higher event reporting delay. On theother hand, Push model has higher energy consumption.Therefore, hybrid model is a natural choice that can beadopted to reduce reporting delay with lower energyconsumption. In heterogeneous sensor network wheredifferent sensor nodes are deployed for light, pressure,temperature etc. In such deployments, it is important thatthe event readings sent by a sensor node should be deliv-ered to only those sensors sensing the same event, e.g. anabrupt change in temperature should be propagated to agroup of temperature sensors to trigger them for possible

occurrence of that event besides the sink nodes. A hybridmodel would be useful in this scenario in which sinknodes can collectevent information from a group of sen-sor nodes having event readings from source nodes as theevent occurs. Obviously, there is an urgent need of sup-porting multicast routing in WSN. Multicast routing hasbeen addressed recently and a number of approaches areproposed based on tree, mesh, geocast and combinationof these configurations.

In this paper we provide an overview of existingmulticast protocols and investigate the performance ofthese protocols with respect to many important parame-ters like overhead, delay, scalability and energy efficien-

cy. The remaining sections of this paper are organized asfollow.In Section II, We discuss taxonomy of multicast rout-

ing. In section III we provide an overview of existing pro-tocols usedfor multicast communication in sensor net-works. We present adetail description of these protocolsand highlight their key points and weaknesses. In sectionIV, we briefly explain our observations with the help oftable. Finally in section, V we conclude the research issuesand future direction for multicast communication in wire-less sensor networks.

2.TAXONOMY OF MULTICAST ROUTING

In this section we discuss that how multicast routingcan be handled in wireless sensor networks. Multicastcommunication is handled with the help of multicastgroups. Each multicast group consists of a number of sen-sor and sink nodes which are interested in receiving mul-ticast data. There is no geographical limitation in these

groups. Each node in multicast group maintains infor-mation about its neighbor nodes. It is important that mul-ticast packets should be delivered reliably to each node inmulticast group and also avoids routing loops as well ascontrol overhead.

For this purpose, many protocols are developedusing different approaches, for example some protocolslike Light weight adaptive multicast algorithm (LAM) [5]and Optimized Distributed Multicast Routing Protocol(ODMRP) [17] use flooding mechanism to send datapackets from source to destination while others usesource-based Trees or Shared Tree mechanism likeMAODV [13], GMR [15] and HGMR [20].

Whenever a node wants to send data to a multicastgroup and if it does not have any pre-established routeinformation then it initiates a route discovery process.Source node discovers route through its neighbor nodeswith each memberof the group, thus a route discoveryprocess configures the node in such a way that a packetoriginating from source node is received by all membersof multicast group. Various configuration techniques areproposed to support multicast routing as classified in Fig.1. The proposed multicast routing protocols are generallybased on one of these approaches and inherit their fea-tures. In the following sections, we provide an insight tothese techniques prior to proceeding for discussion ofprotocols.

2.1 Tree Based Approach

Tree based approach can be further divided into a)Source based tree construction b) Destination based treeconstruction. In source-based tree multicast routing pro-tocols, the tree construction and the tree initiation startsfrom source node, which requires that the source nodemust have information about receivers addresses andtopology of a multicast group.

Fig. 2. Black hole Attack in Wireless Sensor Networks

Fig 1. Different Approaches for Multicast Routing






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Therefore, these protocols have high overhead due to treeconfiguration formed by each source node independently.Incase of mobile sensors the tree configuration is trig-gered frequently that incurs higher overhead as com-pared to the static sensors. However, the tree-based mul-ticast routing protocols require a minimum number ofcopies of each data packet to send to the members ofgroup, which decreases the traffic load and bandwidthutilization. Different algorithms like Multiple DistributionPoint (MDP) [7], Minimum transmission energy (MTE) [8]etc, are used for tree construction.These algorithms are generally applicable when the net-work topologyis static or changes do not affect the con-structed tree. Since reconfiguration or maintenance ofmultiple trees increases control overhead. It is importantthat the protocol must be much efficient and reflect thetopological changes constantly so that the reconstructionof the tree does not cause extra delay in data transmis-sion. Multicast tree is constructed on the basis of differentparameters such as hop count and link quality indicator(LQI) like delay, bandwidth or aggregated weight of the-

se parameters. The tree base approach provides shortestand loop free paths and it is easy to join or leave a mul-ticast group. On the other hand, the drawback of tree basestructure is that any link failure may cause the isolation ofcomplete branch from tree which may have multiplenodes.

2.2 Mesh Based Approach

In Mesh-based approach, all the group membersform mesh connectivity, so that every member has a con-nection with the other members. In mesh structure, routediscovery and mesh construction is accomplished by two

ways a)Through broadcasting b) through central pointsUnlike tree based approach, mesh based approach ismore robust and reliable especially when the nodes mo-bility increases. There are redundant paths to access anynode in the topology. However the main drawback inmesh approach is that it requires more control messagesthan a tree based approach and result in high bandwidthand energy consumption. Mesh-based approach has fewadvantages it eliminates the traffic problem. Because itthere are dedicated links which distributes the loadamong multiple available paths.

This approach is more robust because any link failuredoes not disturb the overall communication. Mesh based

approach has difficulties in configuration which makes itmore costly than other approaches. Similarly direct con-nectivity of a single node with multiple nodesalsoincreases the number of I/O ports.

2.3 Geocasting Based Approach

In multicast communication data is delivered to anumber of nodes which are geographically dispersed in adeployment field and there is no restriction on theboundary for data transmission. In contrast, geocastcommunication has restriction on the boundary of desti-nation nodes in which data packets are delivered to a setof nodes lying within a specific geographical area. A

geocast group member is defined by its geographical lo-cation. Recently many geocast routing protocols havebeen developed like Flooding based, routing-based andcluster-based protocols. Examples of which are Location-Based Multicast algorithm (LBM) [9] and Geocast Adap-tive Mesh Environment for Routing (GAMER) protocols[10]. Fig.3 identifies a geocast group where S node sends

data to number of nodes D in specific area. An advantageof geocast approachis that it performs efficiently in heter-ogeneous networks.However this approach has scalabil-ity limitations therefore it is not suitable in large net-works.

Fig 3. Geocast Communication Scenario

2.4 Rendezvous Based ApproachIn this approach, a subset of nodes or a single

node act as rendezvous points (RP) in the network. TheseRP collect sensed data from different sensor nodes andtransfer them to the sink nodes. RPs are mobile nodes andvisit each node in the network after specific time interval.Any node which want to send data will wait for RP andwhen RP comes in its range than it send data packets to-wards RP which will further deliver it to destination nodein the network [11].A disadvantage of RP is that it is atime consuming approach and any RP failure may cause abig damage in the network.

2.5 Cluster Based Approach

Cluster based routing is a new approach used formulticast communication. In this approach energy-efficient clusters are formed randomly in deployed sensornetworks. Each cluster is managed with the help of clus-ter head CH. Each CH acts as a coordinator which re-ceives messages from the cluster members and transmitsthem towards destination nodes or sink. Cluster memberscan communicate with each other easily but for long-range communication CH are involved for messagestransmission. Clusters are maintained for a short timecalled a round. A round consists of an election phaseanda data transfer phase. Each cluster head is elected af-ter election process in the network. There is possibilitythat after each round different node will act as a clusterhead. All clusters are not destroyed at the end of eachround some cluster may retain for many rounds. Whichreduce the number of head elections and therefore bur-






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den of long-range transmissions is more efficiently dis-tributed among the nodes. Although the cluster headelection is energy consuming. After a specified number oftransmissions, a new set of clusters are formed. Clusterbased approach is an efficient approach. However thereistime consumption in election phase of cluster heads CHs.

3 MULTICAST ROUTING PROTOCOLSIn this section we describe different multicast routing

protocols which are proposed in wireless sensor network.There are many protocols available for this purpose butthese protocols have some issues and challenges accord-ing to todays scenarios. To identify these issues and chal-lenges we give a detail discussion of these protocols andpoint out the advantages and disadvantages of these pro-tocols in sensor networks.

3.1 Branch Aggregation Multicast ProtocolA.Oura et al [12] proposed a multicast protocol for

multicast communication in wireless sensor networks

known as Branch Aggregation Multicast protocol (BAM).BAM protocol use two approaches for communicationI) Single Hop Aggregation (S-BAM) II) Multiple Path Ag-gregation (M-BAM) S-BAM used for aggregation ofradiotransmissions in a single hop. It enables a singletransmissionto multiple receivers in the network. M-BAMused for aggregation of multiple routes into fewer ones. Italso controls the range of radio transmission. S-BAM isespecially designed to reduce redundant communicationsat every branch while M-BAM is designed to reduce thenumber of branches in a tree. These two approaches canbe combined in many situations which are known as (SM-BAM). The combined approach uses the characteristics of

both techniques S-BAM control the redundant communi-cation while M-BAM controls the number of branches inthe tree. This techniques of merging both approacheshelps to reduce overhead as well as energy consumption.The branch aggregation multicast routing protocol do notdivide the network in multicast groups therefore it de-creases communication overhead because there are noextra messages in the network to join a multicast group,leave a multicast group or any acknowledgement fromthe base node in a multicast group. This approach alsodecreases the bandwidth utilization and energy consump-tion in the energy constraint wireless sensor networkswhere we have very limited energy in each sensor node.

This behavior of BAM shows that its an energy efficientprotocol. Another property of BAM protocol is that it canwork with any other protocol in wireless sensor networktherefore this protocol can perform betterinheterogeneous networks where multiple protocols are involved in communication process.However there are still certain research issues which cre-ates problemsI) BAM protocol has scalability issue because anychangein the network may affect the performance of thisprotocol. II) BAM protocol do not support real timecommunication therefore this protocol is not suitable forwireless sensor actor network where we needs in time

events information delivery to actor nodes. Otherwisethe attack may cause a lot of destruction. III) As clearfrom the experiment and simulation in research paper[12] BAM is designed for static networks where both sen-sors as well as sink nodes are static. In case of mobile sen-sors the BAM protocol will be unable to handle the com-munication in wireless sensor network. IV) BAM protocolhas not the ability to create multicast groups and sub-groups in the network therefore in case of large networksthis protocol cannot perform efficiently. V) BAM protocolis an event driven protocol and activated only when anevent occur. Therefore in some networks if we are inter-ested in other information regarding any event to occurthan BAM fails to perform efficiently.

3.2 Multicast Ad-hoc On-demand Distance VectorRoutingProtocol (MAODV)

Multicast Ad hoc On-demand Distance Vector Rout-ing Protocol (MAODV) [13] is an important protocol de-signed for multicast communication in Ad-hoc networks.

However this protocol is implemented in wireless sensornetworks in 2007 by J, Sa, Silva et al [14]. He compares theresults of three protocols AODV, MAODV and a broad-cast approach in its final results. He proved that the per-formance of multicast routing protocol MAODV is farbetter than the other two approaches. MAODV discoverroutes for data transfer in on demand fashion whenever anode wants to send data; it first broadcast the address ofits destination node and then wait for reply from that des-tination. Whenever the destination nodereceives that re-quested packet it reply through the same routeto sendernode and then data is forwarded towards that node.There are some research issues needs to resolve in

MAODV.I) MAODV protocol has high overhead because thisprotocol discover the routes in on demand fashion there-fore before transfer actual data destination address isbroadcast in the network. This technique of the protocoldelivers extra datain the network which causes highoverhead and bandwidth utilization. II) MAODV proto-col has high delay in the sense of message delivery to thedestination node. The source node will wait until a suita-ble route is discovered to access the destination. III)MAODV is an energy inefficient protocol. On demandroute discovery consume much energy on source as wellas other nodes in the route which can be toleratedin wire-less sensor networks having very limited energy. IV)MAODV protocol is not a real time protocol because thereistoo much delay in route discovery therefore this proto-col is unable to deliver the data in real time. Because ofthe above drawbacks MAODV is not a suitable protocolfor wireless sensor actor networks (WSANs).

3.3 Geographic Multicast Protocol

Juan A. Sanchez et al proposed another protocolbased on geocast approach [15] in 2006 known as (GMR)Geographic multicast protocol. GMR protocol was muchefficient and reliable protocol for multicast communica-tion. However the main drawback of this protocol was






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high overhead and maximum bandwidth utilization. Toresolve these issues the author by itself in 2007 makes itbandwidth efficient [16]. GMR usedits neighbor infor-mation to forward the data packets from source to desti-nation. Therefore it is necessary that each nodemay knowabout its neighbors. The bandwidth utilization and over-head is decreased to avoid flooding in GMR protocol.Whenever a node wants to send data it simply forward itto its neighbor who has information about their ownneighbors so the data is forwarded towards destinationwithout overhead but still it faces delay.

The protocol performance is measured through costover progress scheme where cost is number of neighborselection, if number of neighbor selected is high it meansthat the cost will be higher similarly the progress isachieved when the data packet become nearer to the des-tination in each step. As discussed that GMR protocol is alocalized protocol and depends on the neighbor infor-mation therefore it does not required broadcast techniquefor data delivery to multiple nodes. GMR protocol is de-signed for small networks with low or medium number

of nodes therefore GMR protocol will not efficiently per-forms in large and dense networks. GMR protocol usescombination of tree based and Geocast based approachesfor multicast communication. After above discussion wecan easily point out many problems in GMR protocolsuch as.

I) Although GMR protocol resolved the issues ofbandwidth utilization and overhead as compare to itsprevious version but still because of neighbors infor-mation forwarding too much overhead is generated in thenetwork that is not feasible and affordable especially forsensor nodes with lower energy. II) GMR protocol hasscalability issues because it is designed for small net-

works with low or medium node density therefore it willperform poor in large networks as well in highdensitynetworks. III) GMR protocol is an energy ineffi-cient protocol thats why not suitable to implement inwireless sensor networks. Similarly it also exhibits highdelay in communication. IV) The major drawback ofGMR protocol is that it does not support real time com-munication which may cause destruction at large levelinside the networks.

3.4. Optimized Distributed Multicast Routing Pro-tocol (ODMRP)

Yang Min et al proposed a distributed protocol for

multicast routing in wireless sensor network known asOptimized distributed multicast routing protocol(ODMRP) [17]. This protocol is an improved version ofdistributed multicast routing protocol (DMRP) [18]. Themajor problem in old protocols was that they did not con-sider multi sinks in the network. ODMRP use tree basedapproach for multicast communication.The constructionof the multicast tree is based on shortest path from sourceto sink node. In ODMRP protocol the communicationprocess is initiated from the source node thereforeODMRP is source based tree protocol. Whenever a specif-ic event occurs than the source node flood the invitationmessage towards all sinks nodes in the network. After

receiving the invitation message sink nodes send an ac-knowledgment to source node for confirmation. All nodesthrough which the invitation message passed andreached to sink nodes and then again followed byacknowledgement messages sent by sink nodes stores thewhole routes IDs. This is basically a two phase processwhere invitation message is first sent and then acknowl-edgement is received. However this protocol has certainlimitations, such asI) ODMRP protocol has high overhead because of thetwophase communication problem in which invitationmessage is flooded and then acknowledgement is trans-ferred. II) ODMRP has high delay because of route estab-lishment between source and multiple sinks. II) ODMRPis also an event driven protocol like BAM. Therefore itcannot perform efficiently whenever we need data with-out any event occurrence in the network.IV) This protocol is an energy inefficient protocol becausea lot of energy is consumed in forwarding invitation mes-sages and then wait for acknowledgement message. V)ODMRP protocol does not support real time communica-

tion which is necessary for in time information delivery tointerested nodes.

3.5 Hierarchical Rendezvous Point Multicast(HRPM)

Hierarchical Rendezvous Point Multicast (HRPM) isanother protocol proposed for multicast communication.HRPM was first designed for ad-hoc network and thenimplemented in wireless sensor network in 2007 [19] [20].As clear from its name this protocol HRPM uses a hierar-chy for data forwarding from source to destination.Therefore it has no cost maintenance like GMR protocol.HRPM protocol constructs different trees for multicast

communication and uses geographic forwarding fortransferring of data down the tree because of extra bur-den of tree construction and geographical forwarding itconsume a lot of energy therefore its an energy inefficientprotocol. Another property of HRPM is division of net-work in multicast groups and then into subgroups.Eachsubgroup is controlled by its coordinator that is alsocalled access point (AP).

All access points (APs) are connected with Rendez-vous point (RP). This hierarchical distribution of work inthe network reduces overhead as well as bandwidth utili-zation. There are many advantages as well as challengesin this protocol likeI) HRPM protocol has lower commu-

nication overhead than GMR protocolbecause of the hier-archical setup. II) Delay in HRPM is also lower than GMRprotocol it maintain certain information. III) This protocolis a scalable protocol and itsperformance does not de-crease due to any changes in network size or node densi-ty. IV) HRPM is an energy inefficient protocol. V) Thisprotocol also does not support real time routing.

3.6 Hierarchical Geographic Multicast Routing(HGMR)

Dimitrios Koutsonikolas et al proposed a newprotocol for multicast communication that is combinationof two important protocols GMR protocol and HRPM






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protocol. HGMR [20] protocol inherit the quality ofHRPM protocol in scalability, Delay, overhead and stateinformation maintenance. Howeverit also resolves theissue of energy inefficiency exist in HRPM and GMR pro-tocol. This protocol does not waste the nodes energy.HGMR protocol handles the efficient routing withthehelp of multicast groups.

Each multicast group is controlled with an accesspoint (AP) as used in HRPM protocol but in HGMR pro-tocol numbers of access points (APs) are not too large asin HRPM. Each access point (AP) uses differentrelaypoints for data forwarding. From above discussion itis clear that HGMR protocol satisfy most requirements ofmulticasting in wireless sensor networks. However thereare still some problems in HGMR protocol. Those areI) HGMR Protocol do not support real time multicastcommunicationin sensor network therefore not a suitableprotocol for WSANs. Although delay in this protocol iscomparatively lower than other existing protocols.II) HGMR is designed for static wireless sensor networkswhere as in wireless sensor actor network both sensor

nodes and actor nodes are mobile therefore this protocolcannot perform efficiently in mobile scenario of WSANs[20].3.7 Lightweight Protocol for Multicast (TNT/PTNT)

Due to limited resources in wireless sensor networksQingYe, et al [21] proposed a new light weight approachfor multicast communication. He introduced track andtransmit (TNT) approach to check the position of sinknode in the network, a sink node is capable to move fromone place to another place. The new position of the sinknode is tracked everytime and after tracking data is for-warded towards it. Although the TNT approach was not

too much efficient therefore the author also proposed animproved form of TNT known asPriced track and trans-mits (PTNT). The new approach PTNT is more efficientthan TNT as clear from simulation results [21].

As compared to TNT and VLM2, which are old ap-proaches, PTNT has lower overhead and delay. Maxi-mum number of packets is received in PTNT at destina-tion. This approach has a unique ability to easily imple-ment in static and mobile scenarios of wireless sensornetwork. The sink nodes broadcast beacon messages con-tinuously in the network which increases bandwidth con-sumption and network overhead. When a sensor nodereceive the beacon it acknowledge with its shortest path

information. PTNT consider the distance to destination asa price [22] and as much distance to destination is de-creases price is also decreases therefore PTNT give theguarantee that after each routing step the data packet willbe more nearer to destination as compare to previous lo-cation. This protocol is designed for small networks there-fore any change in network size and node density affectsthe performance of this protocol. It also consumes a lot ofenergy by continuously sending beacons and receivingacknowledgements therefore its an energy inefficientprotocol. The LWMP protocol resolves certain issues ofdelay and mobility in multicast communication but stillthere are few research issues in this protocol due to which

this protocol is not feasible for implementation in wirelesssensor actor network (WSAN). This protocol has somedrawbacks such asI) LWMP has high overhead because of its extra trafficgenerated for tracking and transmission. II) This protocolcannot handle the mobility of sink node whenever itmoves backand forth in the network although we cannot

restrict a nodes movement. III) LWMP is an energy inef-ficient protocol due to high consumption of energy. IV)LWMP has scalability issues and any change in the net-work size and node density decreases its efficiency andreliability. V) This protocol does not support real timecommunication therefore cannot implement inwirelesssensor actor networks (WSAN).

3.8 Very Lightweight Mobile Multicast system(VLM)VLM2 is another technique used before LWMP using

PTNTapproach for multicast communication. In this ap-proach everynode is identified by its ID. The ID consistsof multiple portions, personal identification of sensornode, and identificationof that multicast group to whichthis node belongs etc. Whenevera sensor node wants tobecome a member of multicast group it send a request forsubscription to any member ofthe multicast group andthen wait for its acknowledgement.

For communication between sensor and sink nodeunicast routing is used in a multicast group while com-munication between sink node and sensor nodes are han-dled with the help of multicast routing [23]. VLM usesflooding mechanism for transfer beacons to under lyingsensor nodes. As clear from research article [21] in whichVLM2 is compared with other protocols shows that thisprotocol has high delay, overhead and scalability prob-

lems. Because of these limitations this protocol is not fea-sible for WSANs.I) VLW is an energy inefficient protocol therefore it isnotsuitable for wireless sensor networks. II) VLM hasvery high overhead, delay and scalability issues. III) Thisprotocol does not support real time communication there-fore not suitable for wireless sensor actor network.

3.9Actor Director Cluster Based Multicast Protocol(ADCMP)

M. A. Khan, G. A Shah et al, proposed a frame-work for multicast communication and coordination inWireless Sensor Actor Networks. The proposed frame-

work is based on Actor Directed Clustering Protocol(ADCMP), which configures all the sensors in the net-work and form different clusters, which propagates anyinformation about an event to their respective clusterheads as well as to nearest actor nodes actors.

The cluster heads in the network are responsible for ef-ficient data delivery to actor nodes without delay whichassists actor nodes in takinga quick action and thus per-forming its role of sensing and reacting in the deploymentfield. ADCMP is an actor directed clustering protocolwhich dynamically forms clusters according to multicastrequirements in which a node, closer to the actor, be-comes a cluster-head for the nodes which are farther.






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Thus the transmission is always directed towards the ac-tor that minimizes the energy consumption in multicastrouting. There are two phases of cluster formation. In thefirst phase, every sensor node broadcast periodicbeaconthat contains the residual energy of node, location, trans-mission power (Pt) in use and probability of cluster head(PCH). Nodes listening such beacons from their neigh-bors maintain a table to record this information. If an en-try already exists in the table, it is updated with the recentvalues. Actors also broadcast their location periodically orwhenever their location is changed.

4SUMMARY OF WSN,S MULTICAST PROTOCOLS

In this section we give a brief description about behav-ior and properties of each protocol with respect to differ-ent parameters like overhead, delay, scalability, stateless,energyefficiency, multicast groups and real time commu-nication. The table 1 shows that each protocol has certainadvantages as well as some drawbacks. Every protocolexhibits different behavior under same conditions. Many

routing protocols have high overhead which causesgreater energy consumption on the sensor nodes.That why these protocols are energy inefficient protocolswhich is much clear from table 1 column 6 and this posesa major problem for sensor nodes because there is limitedenergy on each sensor node. Similarly maximum proto-cols have scalability issues and any increase in node den-sity as well as network size affects the protocol perfor-mance. Wireless Sensor networks have much significancein real life situations. In many dangerous scenarios it be-comes necessary that the data transfer takes place in realtime. However there is no support for real time routing inexisting multicast protocol (last column of table 1).

5CONCLUSION AND FUTURE WORKIn this paper, a survey on multicast protocols of wire-

less sensor networks is presented. The purpose of thispaper is to discuss different characteristics, approaches,and parameters to identify the limitations in existing mul-ticast routing protocols of wireless sensor networks(WSN). We explain that why these protocols are not fea-sible to implement in Wireless sensor actor networks(WSAN). There are many reasons behind this claim suchas1. The major issue in these protocols is that noexistingmulticast protocol of WSN provide real time mul-

ticast communication which is important in WSANs for intime action against any attack.2. Existing multicast protocols have security issuesandthere is possibility that some important data may beaccessed by any attacker node especially in the battlefield.3. To avoid self destruction due to some ambiguous in-formation and take proper action against an attackWSANs require certain level of QoS which is not provid-ed by existing multicast protocols in WSNs.4. Due to limited energy in sensor nodes we shouldbemore conscious about energy consumption althoughthe existing multicast routing protocol are energy ineffi-

cient however wecannot afford too much energy con-sumption is WSAN.We believe our survey will be very useful to the researchcommunity and also serve as an introductory support formulticast communication in wireless sensor networks.A. Future WorkUp to date many efforts have been done in the researchcommunity to make the multicast communication moreefficient and reliable. However there are still many issuesthat should be resolved and keep in mind while design-ing a new multicast routing protocol. These issues are asfollow1) Real Time Routing: The sensed information should bedelivered to destination without any delay. Because anydelay in case of some emergency scenario cause a big de-struction in the network.2) Scalability: The multicast protocol should be scalable inorder to support any change in the network such as in-crease in number of nodes in a multicast group, mobilityarea and heterogeneity of nodes.3) Security: Security is another challenging issue that

should be resolved for communication among membersof a single multicast group and between multicast groups.4) Energy Constraints: Energy consumption is anotherissue that should be in mind before designing a new mul-ticast routing protocol. Wireless sensor nodes have verylimited energy and it is required that a multicast protocolconsume lower energy to avoid starvation of sensors inthe network.5) Multiple Sources: Most of the multicast routingprotocolsin wireless sensor networks are designed tosupport singlesource multicasting. However there is pos-sibility that multiple sources at a time want to multicasttheir sensed data especially in heterogeneous sensor net-

works. Therefore in such situation existing multicast pro-tocols cannot operate efficiently.At the end we conclude that existing multicast protocolsin sensor network are not suitable for wireless sensor ac-tor networks (WSANs). We intend to investigate differenttechniques for developing a new energy efficient and realtime multicast protocol according to the specific require-ments of WSAN. We also propose a new approach formulticast communicationin WSAN. This new approach isheterogeneous approach and combination of multiplemulticast approaches.

ACKNOWLEDGMENT

We wish to thanks Abdul Wali Khan University Mardan,HEC Pakistan and International Islamic University Islam-abad for their support in this research work.

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TABLE 1.COMPARISON OF DIFFERENT MULTICAST PROTO-COLS IN SENSOR NETWORK

S.No

Protocol Overhead

Delay Scalability

State-less

E.Effi-

cient

RealTime

1 BAM Low Low Yes Yes Yes No2 MAODV High High Yes No No No3 GMR High High No Yes No No4 ODMRP High High Yes No No No5 HRPM Low Low Yes Yes No No6 HGMR Low Low Yes Yes Yes No7 LWMP High Low No Yes No No8 VLMP High High No Yes No No9 ADCMP Low Low No Yes Yes Yes

TABLE 2.EXPLAINATION OF MULTICAST ROUTING PROTOCOLSACRONYM

S.No Protocol/AlgorithmAcronym /Name Protocol /Algorithm Name

1 BAM Branch Aggregation MulticastProtocol

2 MAODV Multicast Ad hoc On-demand

Distance Vector Routing Protocol3 GMR Geographic Multicast Protocol4 ODMRP Optimized Distributed Multicast

Routing Protocol5 HRPM Hierarchical Rendezvous Point

Multicast6 HGMR Hierarchical Geographic Mul-

ticast Routing

7 LWMP Lightweight Multicast Protocol

8 VLMP Very Lightweight Mobile MulticastProtocol

9 ADCMP Actor Directed Cluster Based

Multicast Protocol

M. A. Khan received his BS & MS degree with major Communication& Networks in Computer Science, from International Islamic Univer-sity Islamabad, Pakistan and PhD degree in Wireless Networks joint-ly from University of Missouri, USA and International Islamic Univer-sity, Islamabad, Pakistan in 2011. He worked as a Research Scien-tist at University of Missouri, USA. Later he joined University of Ulmas PostDoc Fellow in 2011. He is currently working as an AssistantProfessor at the Department of Computer Science, Abdul Wali KhanUniversity Mardan, KPK. His main research interests are Routing,






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Security, QoS, Energy Efficiency and Localization in Wireless Sensor& Actor Networks (WSANs). He received HEC fellowship, USAIDscholarship and distinction scholarships from IIUI. He has been in-volved in the review process of various journals Springer WirelessCommunication, Wiley InterScience Wireless Communication &Mobile Computing, Elsevier adhoc networks, IJATIT, IJCSI, etc. andthe conferences; IEEE SCS, WASET, Globecom, INMIAC, WASNet,ICWCMC, and and IEEE ICC etc. He is a member of IEEE Commu-nication Society, Springer and ACM.

Mr. M. Ahsan received his Msc in Computer Science from Int, Islam-ic University Islamabad and MS in Computer Science from EMECollege, Rawalpindi. He is working as an Assistant Professor at thedepartment of Telecom Management Int, Islamic University, Islama-bad. His research interests are wireless networks, security and rout-ing.

Ghalib A. Shah received his Ph.D. degree in computerengineeringfrom Middle East Technical University, Ankara Turkey inJanuary 2007. Heworked as a PostDoc fellow at MiddleEast Tech-nical University, Northern Cyprus Campus in 2007.Later, he joinedCollege of E & ME, National Universityof Sciences & TechnologyIslamabad as an assistantprofessor. He is also awarded aCOMSTECHTWASjoint research grant for young researchers,madein a highly competitive contest. He has been involvedin thereview process of various journals IEEE TVT,Computer Networks,Elsevier adhoc networks etc. and theconferences; PIMRC, MCVT,MCWC, IEEE GlobecomWASNet, WCS, and ISWCS 2006 and IEEEICC etc.His current research interests include multimediawirelessnetworks, next-generation wireless networks, wirelesssensorand actor networks. He is also a member of ACMandAustralian Computer Society.





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Multicast Routing Protocols in Wireless Sensor Networks (WSNs)