Journal of Convergence Informaton Technology A Novel Adaptve Load Balancng Routng Algorthm n Ad hoc Networks Zhu Bn, Zeng Xao-png, Xong Xan-sheng, Chen Qan, Fan Wen-yan, We Geng College of Communcaton engneerng, Chongqng Unversty, Chongqng, Chna coolzhu.bn@gmal.com do: 10.4156/ct.vol5.ssue5.8 Abstract In ths paper a novel adaptve load balancng routng algorthm n Ad hoc networks based on a gosspng mechansm s proposed. Unlke prevously publshed algorthms, ths algorthm adusts the forwardng probablty of the routng messages adaptvely, accordng to the load status and the dstrbuton of the nodes n the phase of route dscovery. The smulaton results show that the algorthm sgnfcantly reduces the routng overhead, and balances the load effectvely. Keywords: Ad hoc networks, routng algorthm, load balancng, gosspng mechansm 1. Introducton A moble Ad hoc network (MANET), whch s a moble communcaton network formed by a collecton of wreless moble nodes wth transcevers, has drawn much attenton as a key subect n recent years. The node n MANET has the functon of both host and router. All the nodes are capable of arbtrary movement and can choose to enter or wthdraw from the network freely. Dfferent from wred network, MANET s able to spread quckly wthout the help of exstng nfrastructure wth the characters of non-center, self-structure and self-repar. MANET has better robustness and capablty of resstance aganst destructon, hence, ts applcaton s promsng n battlefeld, rescue and other felds demandng temporary communcaton network. In MANET, due to the lmted propagaton range of the transcever at each moble node, t may be necessary for one node whch can t communcate wth other nodes drectly to seek the ad of some medate nodes to forward packets to the destnaton. In the meantme, the arbtrary movements of nodes may dynamcally change the network topology structure formed by wreless channels. Addtonally, both the bandwdth and battery power are scarce resources at moble nodes. So the tradtonal routng protocols could not be appled to MANET. Hence, the desgn of the routng protocol for MANET becomes a vtal ssue. Many routng protocols have been developed and these protocols may generally be categorzed as table-drven and on-demand routng. Table-drven routng protocols attempt to mantan consstent and up-to-date routng nformaton at each node of the network. Such protocols requre regular updatng to meet the dynamc change of network topology, so they ncur vast traffc stream and routng overhead. On the other hand, on-demand routng protocols overcome ths lmtaton. They don t mantan routng nformaton at every node, but create routes only when desred by source nodes. Therefore, on-demand routng protocols have been wdely used n MANET. Most of the on-demand routng protocols usually select the route of fewest hops. The use of shortest path routes performs well n wred network. However, n MANET there s a tendency to use a few centrally located nodes n a large number of routes, thus ths scheme of route selecton wll lead to congeston of some central nodes. Such nodes have to carry excessve load and would suffer from hgh power consumpton. Overloaded nodes would cause hgh packet delays and packet drops. Moreover, f the battery power s exhausted, the lfe span of the network s also shortened due to the lack of central nodes. In recent years, the load balancng routng algorthm [1] n moble Ad hoc networks (MANET) has been wdely studed to overcome the shortcomngs of the shortest path routes, and the load condton s used for makng the routng decsons. The ABR algorthm [2], uses the total number of routes through a node to measure ts load condton. On the bass of ABR, LBAR [3] s presented, and t counts n the routes through adacent nodes. Snce the number of routes cannot reflect the load exactly, DLAR [4] uses the number of the packets buffered n the nterface queue of MAC layer as the load metrc. LSR 81
A Novel Adaptve Load Balancng Routng Algorthm n Ad hoc Networks Zhu Bn, Zeng Xao-png, Xong Xan-sheng, Chen Qan, Fan Wen-yan, We Geng [5] s smlar to DLAR wth a further consderaton on the packets queung n the nterface of the adacent nodes, and proposes a path comparson functon. Most of the routng algorthms n MANET are based on some varant of floodng mechansm. The use of the floodng causes a lot of redundant routng messages to be propagated, and wastes much network power. Therefore, the gossp-based routng whch can reduce the redundant messages draws great attenton. In Ref. [6], Zygmunt J. Haas et al. dscuss the effect of the basc gosspng mechansm appled to routng n MANET, and present some optmzatons of gosspng to enhance the performance. In ths paper, a novel adaptve load balancng routng algorthm based on a gosspng mechansm (ALBR-G) s proposed. Ths algorthm combnes the dea of load balancng and the gossp-based routng and s very effectve to acheve load balancng n the network and reduces the routng overhead. Ths paper s organzed as the follows: n Secton 2, the desgn concepton n ALBR-G s descrbed and the detals of ALBR-G are explaned. Smulaton result and analyss are reported n Secton 3. Fnally, Secton 4 presents conclusons. 2. Adaptve load balancng routng algorthm based on gosspng mechansm 2.1. Some defntons In ths paper, we assume that there s no undrectonal lnks n the network, and each node s capable to get the nterface queue length n the MAC layer. Defnton 1 Node v samples the nterface queue length n the MAC layer perodcally. q ( k ) s the kth sample value, and N s the samplng tme over a perod of tme, then the load of node v s defned as followng: N q ( k) k 1 LB() (1) N Defnton 2 The total length of nterface queue of node v n the MAC layer s q max (), then the load ntensty functon of node v s defned as followng: LB() LIF() qmax () (2) Defnton 3 We assume the number of neghborng nodes of v s n, and all the load ntensty functons are known, as well as the LIF( ) value of v tself. We sort these n 1 values n the ascendng order, and get a sequence number named as R () (1 R ( ) n 1) correspondng to the LIF() of v. The forwardng probablty of the route request message (RREQ) for the node v s gven by the followng expresson: 1, f (( R( ) 4) or( n 4)) P R () 1, else n 1 (3) From (3), we know 0 P 1,and P s related to the exstng load of v. It depends on the relatve sze of the load ntensty of v n local regon. The smaller the relatve load ntensty s, the larger the forwardng probablty wll be, and the node wll on the route preferentally; on the other hand, the node wth relatve heaver load s of smaller forwardng probablty of RREQ, hence the probablty of onng the route s reduced. Thus the overloaded nodes are protected by usng the nodes of lghter load to establsh the route, so as to balance the network load and lessen the congeston of the network and mprove the data transmsson effcency. In ad hoc networks, nodes are not unformly 82
Journal of Convergence Informaton Technology dstrbuted, and the densty of nodes vares from areas. From (3), we can see that where the densty s hgher (that means n s larger), P s smaller, thus the redundant forwardng of RREQs and the routng overhead are reduced. Where the node densty s lower, P s larger, thus the probablty of route establshment s ncreased. To prevent premature gossp death of RREQs n the course of the route establshment, t s regulated n (3) that: f the sequence number s wthn the range of the top 4 or the nodes are very sparse ( n 4 ), then the forwardng probablty s 1. From the analyss above, we can see that t dffers from the exstng gossp algorthms whch use a fxed gossp probablty, and P s able to adust adaptvely accordng to the nodes dstrbuton n local regon and the relatve sze of the load. The redundant transmsson of the routng messages s reduced and the network load s balanced at the same tme. 2.2. Descrpton of ALBR-G The ALBR-G s based on AODV [7], whch s a well-known on-demand routng protocol, and contans two phases: route dscovery and route mantenance. To obtan the load condton of the neghborng nodes so as to calculate the forwardng probablty, ALBR-G extends the HELLO packet n AODV, and adds the load ntensty functon ( LIF ) to the HELLO packet as an accessonal part. ALBR-G uses HELLOe to denote the extended HELLO packets and other control packets keep nvarant. Every node samples the nterface queue length n MAC layer perodcally, and fgures out the LIF by formula (1) and (2). Before broadcastng HELLOe packet perodcally to neghborng nodes to exchange nformaton, the node nqures ts current load ntensty functon frst, and updates the HELLOe packet. Gossp type used by every node n ALBR-G can be denoted as gossp( p, k, m, n ), where P s the forwardng probablty defned by formula (3), and n s the number of neghborng nodes. Source node starts a route dscovery process by broadcastng a route request (RREQ) packet to neghborng nodes. The processng procedure of ntermedate nodes s descrbed as followng: when a node v has receved a RREQ from neghborng node v, t wll udge f the RREQ s a new packet. If so, and t s not the destnaton node, then the hop count n RREQ wll be compared wth parameter k. If t s fewer than k, t means v s n the range of the frst k hops from the source node. Therefore, RREQ wll be forwarded wth the probablty 1 to prevent premature death of RREQ at the begnnng of gossp. If the hop count s more than k, then P can be fgured out by formula (3), whch s used as the forwardng probablty of RREQ. If v decdes not to forward RREQ accordng to P, RREQ wll not be dscarded mmedately. It wll be cached for a perod of tme whch s set to T out. Wthn the allotted tme, f the number of same RREQs receved from neghborng nodes by v reaches m, we can beleve that there are adequate nodes to on n establshng route, and the probablty of gossp death s low. Then v wll dscard RREQ from cache, or else, v wll broadcast RREQ to neghborng nodes, so as to make tself on the route. In ALBR-G, T out s set to be 4 tmes of NODE_TRAVERSAL_TIME, where NODE_TRAVERSAL_TIME s a parameter n AODV whch presents the estmated tme of the average one hop traversal tme for packets. When the destnaton node receves the frst RREQ, a route reply (RREP) packet wll be sent to the source node. After source node receves the RREP, t can start data transmsson. The route mantenance phase of ALBR-G s smlar to AODV. When the lnk s dsconnected, the upstream node ntates the route reparaton. If the reparaton fals, then a route error (RERR) packet wll be sent to source node to restart the route dscovery procedure. 3. Smulaton results and analyss In order to study the performance of ALBR-G n terms of routng overhead and load balancng, smulatons were performed usng NS-2 wth random waypont model [8], and the pause tme s set to 83
A Novel Adaptve Load Balancng Routng Algorthm n Ad hoc Networks Zhu Bn, Zeng Xao-png, Xong Xan-sheng, Chen Qan, Fan Wen-yan, We Geng 3 seconds. There are 100 nodes randomly placed n the network whose sze s 4000m by 2500m, and the wreless transmsson model s Free Space model wth a range of 200m. In gossp( p, k, m, n) of every node, k s set to 2, and m s set to 1. We compare ALBR-G, DLAR and AODV at the same condton, and vary the maxmum speed of nodes to smulate dfferent moblty scenaros. The smulaton tme s 500s; all the results are the averages of 20 runs of smulatons. Fgure 1 shows the relatonshp between maxmum speed and routng overhead. As can be seen n Fgure 1, the new algorthm ALBR-G greatly reduces the routng overhead. ALBR-G demonstrates up to 45% less routng overhead than DLAR and AODV. Ths performance gan s obtaned manly from the suppresson of RREQ packets. Dfferent from DLAR and AODV that flood RREQs over the network durng the route dscovery procedure, gosspng mechansm s appled to ALBR-G, and the gosspng probablty can adust accordng to the ambent condton. So the unnecessary propagaton of RREQ packets are prevented effectvely n ALBR-G and the overall routng overhead s reduced a lot compared wth DLAR and AODV. Fgure 1. Routng overhead versus max speed Fgure 2 dsplays the total load dstrbuton over the nodes n the network after the smulaton. The total load of a node s defned as the area under the graph when the load ntensty functon of the node s plotted over tme. So t can represent the load status for a node. From Fgure 2 we can observe the total load dstrbuton fluctuates very much for DLAR and AODV. For ALBR-G, However, the total load s more evenly dstrbuted among the network nodes than DLAR and AODV. As shown n Fgure 2, the new algorthm effectvely balances the load n the network. Fgure 2. Total load versus node ID 84
Journal of Convergence Informaton Technology 4. Conclusons Ths paper proposes a novel adaptve load balancng routng algorthm n Ad hoc networks based on a gosspng mechansm (ALBR-G). Ths algorthm combnes gossp-based routng and the dea of load balancng effectvely. It can adaptvely adust the forwardng probablty of RREQ messages accordng to the dstrbuton and load status of nodes n route dscovery phase. Smulaton results ndcate that, compared wth DLAR and AODV, ALBR-G can sgnfcantly reduce the routng overhead, and balance the load n the network. 5. Acknowledgment Ths research was supported partly by Natural Scence Foundaton of Chongqng of Chna (CSTC, 2008BB2313) and also n part by Chongqng Key Scence and Technology Specal Proect (CSTC, 2009AB2146). 6. References [1] Toh Cha Keong, Le Anh-Ngoc and Cho You-Ze, Load Balanced Routng Protocols for Ad Hoc Moble Wreless Networks, IEEE Communcatons Magazne, Insttute of Electrcal and Electroncs Engneers Inc., Vol. 47, No. 8, 2009, pp. 78-84. [2] Toh C K, Assocatvty-Based Routng for Ad-hoc Moble Networks, Wreless Personal Communcatons Journal, Kluwer Academc Publshers, Vol. 4, No.2, 1997, pp. 103-139. [3] Zhou A and Hassanen H, Load-balanced wreless ad hoc routng, n Canadan Conference on Electrcal and Computer Engneerng, Vol. 2, pp. 1157-1161. 2001. [4] Lee S J and Gerla M, Dynamc Load-Aware Routng n Ad Hoc Networks, n IEEE Internatonal Conference on Communcatons, Vol. 10, pp. 3206-3210, 2001. [5] Wu K and Harms J, Load-senstve routng for moble ad hoc network, n Tenth Intl. Conf. on Computer Communcatons and Networks Proc, pp. 540-546. 2001. [6] Zygmunt J. Haas, Joseph Y. Halpern and L (Erran) L, Gossp-based Ad Hoc Routng, IEEE/ACM Transactons on Networkng, Insttute of Electrcal and Electroncs Engneers Inc., Vol. 14, No. 3, 2006, pp. 479-791. [7] Perkns C E, MroyeR E and Das S, Ad-hoc On-Demand Dstance Vector (AODV) Routng, Internet-Draft, draft-etf-manet- aodv-02.txt, Nov. 1998. [8] Network Smulator NS2. http:// www. s.edu /nsnam/ns. [9] Noor Mast, Muhammad Nsar Afrd, and KoK-Keong Loo, TCP Performance Analyss n Moble Ad Hoc Networks wth Dfferent Routng Protocols and Varyng Payload, JDCTA: Internatonal Journal of Dgtal Content Technology and ts Applcatons, Vol. 3, No. 1, pp. 123-134, 2009. 85