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International Journal of Computer Applications in Engineering Sciences[VOL I, SPECIAL ISSUE ON CNS , JULY 2011] [ISSN: 2231-4946]A Novel Communication Model to ImproveAODV Protocol Routing ReliabilityAli Nakhaee 1 , Ali Harounabadi 2 , Javad Mirabedini 31 Computer Engineering Department, Islamic Azad University Dezful Branch, Dezful Iran2,3Computer Engineering Department, Islamic Azad University Tehran center Branch, Tehran Iran1 nakhaee.89@gmail.com2 a.harounabadi@gmail.com3 j.mirabedini@gmail.comAbstract— By growing the use of real-time application onmobile devices, there is a challenge to provide reliablerouting algorithm among these devices. We propose a newmethod in route selection for Ad hoc On demand DistanceVector (AODV) routing protocol which increases thereliability of the selected route. In this scheme for eachnode along route discovery, we determine two parameters,to calculate the routes reliability. To ensure the correctnessof our method, we create a Colored Petri Net for theprotocol. By applying the model, results show that therouting reliability is increased in comparison withstandard AODV.Keywords— Mobile AdHoc Networks, Routing, Reliability,Coloured Petri NetsI. INTRODUCTIONMobile ad hoc network (MANET) is an autonomoussystem of mobile nodes. It does not use any pre existinginfrastructure and there is no centralized administration.A node can send a message to a destination node beyondits transmission range by using other nodes as relaypoints and thus a node can function as a router. Due thearbitrary movement of nodes In MANET, the networktopology may change rapidly at unpredictable times[1,2].Because of MANET constraints, conventional routingprotocols are not appropriate for MANETs. Manyrouting protocols such as Ad-hoc On-demand DistanceVector routing (AODV)[3], Dynamic Source Routing(DSR)[4], Temporally Ordered RoutingAlgorithm(TORA)[5] that are specific to mobilenetworking have been proposed.But most of routing protocols focus on routing hopsinstead of concentrating on providing reliable routeswhen selecting routes. These protocols will increase theprobability of using potentially unreliable routes. Thedirect consequence of selecting the route with theminimal hops is that routes will be broken frequentlyand it will require additional time to reconfigure theroute from source to destination, which results inincreased amounts of flooding control packets. Hence,frequent routes breaking will badly affect the utilizationand throughput of ad hoc networks [6].We propose a new method in route selection forAODV protocol which increases the reliability ofselected route. In this scheme for each node along routediscovery, we determine two parameters, queue mean(qmean) and maximum queue (maxq) to calculate thereliability of routes. Number qmean shows the averagequeue length of nodes in the path. Number maxq showsthe maximum queue length of the nodes in the path.Every node along route discovery, records thisparameters in Route REQuest (RREQ) packet. In thedestination node, a new parameter is generated frominputs of each route which is called "Reliability Value".We will show that if we use these parameters andmodify the selection criteria in AODV, based on theproposed method, the route reliability will be improved.The rest of this paper is organized as follows. Section2 explains the novel selection criteria in AODV routingprotocol.Section 3 we create a formal model of the modifiedAODV protocol to determine if indeed the protocolprovides the defined service correctly [7].coloured petri nets(CPNs) [8] are a suitable modelinglanguage for verification task, as they can convenientlyexpress non-determinism, concurrency and differentlevels of abstraction that are inherent in routingprotocols [7].Simulation results are given in section4. Finally,Section 5 concludes the paper.II. ADHOC ON DEMAND DISTANCE VECTOR PROTOCOL– AODVAODV is a typical reactive routing protocol. It createsroutes in an on-demand fashion and builds routes usinga route request/route reply query cycle. Also weconsider packets queue length in each node, whenrouting is performed. Number Q_len shows queuelength in each node.When a source node needs to send data packets to adestination node, it first checks its route table to see if ithas an unexpired route to the destination. If it does, it241 | P a g e

Nakhaee et. al.sends data packets using this route immediately.Otherwise, route discovery procedure begins. Wemodified the procedure as follows:Step1: A source node starts to flood RREQ packets toits neighboring nodes in a MANET until they arrive attheir destination node. We add two numbers qmean andmaxq to these RREQ packets.Step2: If the intermediate node N receives a RREQpacket and it is not the destination, then the new valuesof maxq and qmean are calculated in node N. Andinformation of node N is added to the RREQ packetwhich is appended to packet fields. After that, node Nreforwards the packet to all the neighboring nodes ofitself.In node N, maxq is changed if the maximum queuelength in the node is higher than the current maxq in theRREQ received message. Equation (1) shows how tocalculate qmean in the node N.(1)Step3: If node N receives a RREQ packet and node Nis the destination, it waits a period of time. Therefore,the destination node may receive many different RREQpackets from the source. Then it calculates the value ofreliability value for each path from source to thedestination using the information in each RREQ packet.Equation (2) shows how to calculate reliability value(R_degree). Finally, destination node sends a RouteREPly (RREP) packet along the path which has amaximum reliable value.(2)Variable nohop presents hop numbers in routing.We exceeds with presenting a CPN model formodified AODV protocol. Our model is based on themodel which is presented by xiong et al. We considerAODV protocol has four states [9]: RoutCheck: Check the route table to see if the nodehas an existing and valid path to the destination. RREQInit: Initiate RREQ message when necessary. RREQProcess: Process the incoming RREQmessage and output proper results.RREPProcess: Process the incoming RREP messageand output proper resultsIII. CPN MODEL OF A MANET WITH AODV ROUTINGPROTOCOLA. Colored Petri NetsColoured Petri Nets were introduced by Kurt Jensenin 1987 as a developed model of Petri Nets. ColouredPetri Nets are appropriate tools for mathematical andgraphical modeling. Coloured Petri Nets have numerousapplications, and lots of research has taken place withrespect to modeling, describing and analyzing systems,which have synchronized, asynchronized, distributed,parallel, non-deterministic or random natures. In fact,Petri Nets are models which could represent theperformance and state of the system at the same time.A formal definition of CPN is as follows [8]:A Coloured PN (CPN) is a 6-tuplewhere1) P = denotes a finite and non empty setof Places.2) T = denotes a finite and non empty setof Transition.3) C is a colour function that assigns a finite and nonemptyset of colors to each place and a finite and nonemptyset of modes to each transition.4) Denote the backward and forwardincidence functions defined by , such thatDenotes a function defined on P, describing theinitial marking such thatB. CPN Model for Modified AODV Routing ProtocolThe hierarchy page (Jensen) of our CPN model isdepicted in Figure 1. It explains the overall organizationof the modules comprising the CPN model of ourMANET. Page Prime#1 is the top level of our Model fora MANET. And the second level (page Node#2) is thenode template for implementing AODV protocol. Herewe can create model for any MANET composed ofnodes as many as allowed by instantiating this nodetemplate using CPN TOOLS [10]. The third level hasthree pages (page RREQInit#4, page RREQProcess#5and RREPProcess#6), each of which is named by anAODV state as given in [9]. Page SendMsg#3 sendsnode messages in the network.Fig. 1. The hierarchy pageIf we want to create a node instance in a MANET, wecan simply do it by instantiating the node template. Likean object in an object oriented programming language,every instantiated node has its own local variables andprovides interface to the outside world. In our CPN242 | P a g e

A Novel Communication Model to Improve AODV Protocol Routing ReliabilityNode Broadcasting an Incoming RREQ Message to itsNeighboring NodesIf a node receives a RREQ message, then it entersRREQProcess state, which is represented by thesubstitution transition RREQProcess in Fig. 3. Fig. 6shows the detailed information regarding RREQProcess.[9]The actual function of subpage RREQProcess is toinitiate the corresponding RREP message if possible orforward the RREQ message if necessary. Uponreceiving a RREQ message the transition BIDCheck isenabled, thus entering the RREQProcess state for therouting protocol. If the received RREQ message is fresh(received for the first time), it is directed to the placeNewBid. Otherwise it is simply discarded. Thisfunctionality is achieved by the arc inscriptionarc_newbid(bid,sid,lst,sseq,did,dseq,preid,nohop,qmean,maxq).for detailed information on the implementation ofthis function refer to row6 in table1 in appendix. Afterthe place NewBid gets the token for a fresh RREQmessage, either the transition SendRREP or thetransition Broadcast2 is enabled. If the node is thedestination or has a valid route to the destination,guard_sendRREP( ) returns true. Otherwise, the guardguard_broadcast2( ) returns true. For detailedinformation of these two functions refer to rows 7 and 8in table I. If its SendRREP’s turn, the node waits for atime period. (Determined by place Timer). Therefore,the destination node may receive many different RREQpackets from the source. For each received RREQmessage, function arc_setreliable () calculates itsreliability value and checks weather this value is higherthan the reliability value of the previously receivedmessage, if yes then it add the message to place Maxreliable.Otherwise it discards the received message. As a resultof using this procedure the most reliable RREQ packetwould be selected.If the node isn’t the the destination for the RREQmessage, transition Broadcast2 is enabled and performsthe following tasks:1-increases the number of hops by one2-calculates new qmean value3-change the value of maxq if necessaryAnd after these steps, transition Broadcast2 directs thereceived RREQ message to place out.3) Nodes Send their Messages to NetworkNodes send their messages to the network from placeout. Output arc from OUT connected to subpageSendMsg. Fig. 7 shows SendMsg subpage. SendMsgdetermines next node(s) that must be deliveredmessage(s). It`s functionality is according to messagetype. If message type is Route Reply, message isdirected to transition SendRREP. This transitionforwards the message to the next node which must bedelivered this message. If message type is Rout Request,message is directed to transition SendRREQ. TransitionSendRREQ finds all neighbors for the current nodewhich broadcasts the RREQ message and deliver themessage to them. Transitions AddLink and DeleteLinkand place topology specifies nodes mobility in thenetwork. Place topology keeps neighbors list for eachnode. Transition AddLink models that a new linkbetween two ad-hoc nodes arises, and transitionDeleteLink models that an existing link between two adhocnodes disappears.Fig. 7. SendMsg subpageC. Global DeclarationsThe global declarations comprise the color sets andvariables for the AODV. Fig. 8 presents color sets andvariables. The color sets show data structures storingdifferent routing information such as route entry, RREQand RREP messages [9]. The color set RoutMsg definesthe routing message. It contains the following fields:BID: Broadcast ID.SID: Source node that initiates RREQ message.(BID,SID) uniquely specifies a RREQ message.DID: Destination node.INT: Distance from the sender that initiates the message.The sender is DID for RREP message and SID forRREQ message.TYPE: Type of the message. Q means RREQ, and Pmeans RREP.DUMMY: only useful for RREP message. Next node towhich the message is sent. It is set to 99 if the messageis of type 99.DSEQ: Most recent recorded sequence number fordestination DID.PID: The immediately previous node from which thenode receives the message.Qmean: average queue length of the nodes in the path.Maxq: maximum queue length of the nodes in the path.The color set BufferREQ (line 9 in Fig. 8) definesbuffered identification of RREQ message that a nodehas processed.245 | P a g e

Nakhaee et. al.The color set RoutTable (line 17 in Fig. 8) defines thestructure of a route entry in route table. It contains thefollowing fields:DID: Destination of the route.NID: Next node on the route to DID.DSEQ: Most recent recorded sequence number fordestination DID.INT: Distance from the destination DID, measured inthe number of hops that need to be traversed to reachDID.LIFETIME: Remaining time before the route expires.R_degree: Route reliability degree.colset INT = int;colset LIFETIME, BID,DSEQ, SSEQ, DEST, DUMMY,Node_id,Q_len = INT;colset DID, SID, NID, PID = Node-id;colset Qmean, Rlb: realcolset TYPE = with P|Q;closet Maxq = Q_len;colset RoutMsg = productBID*SID*SSEQ*DID*DSEQ*PID*INT*TYPE*DUMMY*Qmean*Maxq;colset BufferREQ = product BID*SID*INT*PID*Qmean*Maxq;colset bufferReqList = List BufferREQ;var lst: bufferReqList;colset Topology = product Node-id * Node-id;colset AHTopology = List Topology;colset INTxINT = product INT*INT;colset INTxINTxINT = product INT*INT*INT;colset RoutTable = product DID*DSEQ*INT*NID*Rlb*LIFETIME;colset routTabList =list RoutTable;var routlst : routTablist;var wait, lifetime : TIME;var bid, sseq, dseq, hopn: INT;var rlb,rrlb: Rlb;var sid, did , selfid, preid : Node-id;var adhoc-topology : AHTopology;var bbid, ssid, ddid, ddseq : INT;var qmean : Qmean;var maxq,qlen : Q_len;var nohop, dest, n, nexthop : INT;var ptype: TYPE;var nid,pid : NID;var msg, routMsg : RoutMsg;var i: Node-id;Fig. 8. Color sets and variablesTABLE1– FUNCTIONS LISTNumber Function1 fun has_validRout(did,[])= false|has_validRout(did,(ddid,dseq,I,nid,lifetime)::rest)=if (did = ddidandalso lifetimeadd_rout(did,dseq,nohop,nid,0,routlst,rrlb)|2 =>routlst;fun arc_forward RREP(sid,selfid,bid,lifetime,did, dseq,n,hop,lst,rrlb)=If(sid selfid)then 1’(bid, sid, lifetime, did,dseq, selfid,nohop+1,p,rrlb,get_pid(bid, sid,lst))else emptyfun arc_newbid(bid,sid, lst,sseq, did,dseq,pried,nohop, qmean,maxq)=if has_id (bid, sid, lst)then emptyelse 1’(bid, sid, sseq, did, dseq, pried,nohop,q,99,qmean,maxq);fun guard_sendRREP(did,routlst,dseq,selfid)=if((dseq get_dseq(routlst)andalsohas_validrout(did,routlst))orelse(did=selfid))andalso (timerrlb1 orelselifetime>100) then 1elseif( did=ddid andalso rrlb

A Novel Communication Model to Improve AODV Protocol Routing Reliabilityremove_rout(did,(ddid,ddseqer,ii,nnid,lifetime)::rest)=if(did=ddid)then restelse(ddid,ddseqr,ii,nnid,lifetime)::remove_rout(did,rest);fun has_id(bid, sid,[])=false13 | has_id(bid, sid,(b,s,h,p)::rest)=if(bid=b andalsosid=s )then trueelse has_id(bid, sid, rest)fun arc_setreliable (did, selfid, bid, sid, dseq,14 preid,routlst,qmean,maxq)=if (did= selfid) thenif(set_reliability(set_qmean(qlen,qmean,nohop),maxq,rlb) then1`(bid,sid,0,did,dseq,selfid,1,p,preid,rlb)else emptyelseif(set_reliability1(set_qmean(qlen,qmean,nohop),maxq,rlb)) then1`(bid,sid,0,did,dseq,selfid,1+get_hop(did,routlst),p,preid, rlb)else emptyfun guard_sendRREP2( lifetime ,wait)=15 if (wait > lifetime) thentrueelsefalsefun set_qmean(qlen,qmean, hopno)=16 (((hopno -1) * qmean + (1/qlen))/hopno)::qmean ;17 fun set_maxq (maxq, qlen) =if (qlen>= maxq) then18qlen :: maxq;fun set_reliability(set_qmean(qlen,qmean,nohop), maxq,nohop,[])=if (nohop>1) then((3*qmean+2*1/maxq+1/nohop)/6 :: rlb;else(3*qmean +(1/nohop))/6 :: rlb ; |set_reliability (set_qmean(qlen,qmean,nohop),maxq, nohop,rlb)=if (nohop>1) thenif (((3*qmean+2*(1/maxq)+1/nohop)/6)>rlb)then((3*qmean+2*1/maxq+1/nohop)/6 :: rlb;else emptyelseif ( (3*qmean +(1/nohop))/6)>rlb)then(3*qmean +(1/nohop))/6) :: rlbelse empty19 fun set_reliability1(set_qmean(qlen,qmean,nohop), maxq,nohop,rlb)=if (nohop>1) then(((3*qmean+2*(1/maxq)+(1/nohop))/6)+rlb)/2):: rlb ;else(((3*qmean +(1/nohop))/6)+rlb)/2 :: rlb ;IV. SIMULATION AND COMPARISONWe present our CPN model for modified AODVprotocol and compared it with CPN model presented byxiong et al[9] for typical AODV protocol. We use CPNTools to run our simulation. Table II shows the numberof broken routes in both typical AODV protocol andmodified AODV protocol where the variable parameteris time, showing that modified AODV algorithm cangreatly decrease the broken numbers of routs.Fig. 9 shows the improvement rate of routingreliability when comparing modified AODV withtypical AODV, indicating that the improvement becomemore significant when time increases. The averageimprovement rate reaches about 80%.Total timeTypicalAODVProtocolModifiedAODVProtocolTABLEI IBROKEN ROUTE NUMBERS100 200 300 40014 23 34 39359V. CONCLUSION12500441460053We present a hierarchical CP net for a MANET whichis used AODV routing protocol. There exists for eachnode in the model a CPN subpage. Also we consider aCP net for the states that a node receiving, sending, andprocessing messages. In our model we use a newmethod to show network topology and also modifiedroute selection criteria in AODV protocol according toaverage packet queue length and maximum packetqueue length in the nodes along the path. Our formalCPN models prove that if we use new selection criteriain routing the route reliability will be improvedconsiderably.Fig. 9. Performance improvement of routes reliability17247 | P a g e