Link Optimization Ad-hoc On-Demand MultipathDistance Vector Routing for Mobile Ad-hoc

NetworksBo Xue

Xi’an Jiaotong UniversityDepartment of Electronic Engineering

Xi’an 710049, ChinaEmail:xbo@stu.xjtu.edu.cn

Pinyi RenXi’an Jiaotong University

Department of Electronic EngineeringXi’an 710049, China

Email:pyren@mail.xjtu.edu.cn

Shuangcheng YanXi’an Jiaotong University

Department of Electronic EngineeringXi’an 710049, China

Email:pyren@mail.xjtu.edu.cn

Abstract—In Mobile Ad-hoc Networks (MANETs), Multi-path routing is wildly researched for its superiority over sin-glepath routing. Ad hoc On-demand Multipath Distance Vector(AOMDV) Routing Protocol performs very well and has beenextensively studied. We present an efficient multipath routingalgorithm, called Link Optimization Ad-hoc On-Demand Mul-tipath Distance Vector Routing (LOAOMDV). We use 4 biesinformation of the RREP (Route Request) packet, and present anew route reply process. The new routing protocol establishes theomitted reverse path and reduces the number of common nodein several paths. This protocol can reduced the end-to-end delay,extend the network lifetime, and salvages packet timely, reducesthe ratio of packet chaotic sequence. Specifically the protocol hasno additional routing overhead. The simulation results provedthat it is more effective.

Index Terms—transmission, common, redundance, routingoverhead.

I. INTRODUCTION

MANET is a set of wireless mobile nodes that form adynamic autonomous network without fixed infrastructure. InMANET, a remote mobile node interconnection is achievedvia peer level multi-hopping technique. This implies that theinterconnection topology can change dynamically, which givesrising to many challenging research issues. In this environ-ment, ad hoc routing is critical and has to be supported beforeany applications can be deployed for ad hoc mobile networks.

According to the particularity of Ad hoc wireless networkrouting protocols, many routing protocol for Ad hoc networkhave been proposed. They can be divided into two majorclasses: proactive routing protocol and reactive routing pro-tocol [1]. The first is proactive routing protocol. For example,the Destination Sequenced Distance Vector (DSDV) protocol[2] proposed by Charles E. Perkins, is one of well-knownproactive routing protocols.But in all proactive routing pro-tocol, node needs to broadcast the route information of thewhole network periodically. It requires much routing overhead.For reducing the routing overhead, the on-demand protocolsare designed. Many reactive routing protocols are proposed.For example, the Dynamic Source Routing (DSR) protocol[3], the Ad hoc On-demand Distance Vector (AODV) protocol

[4], the Associativity Based Routing (ABR) protocol [5], andthe Temporally-Order Routing Algorithm (TORA) protocol[6]. Reactive routing protocol initiates route computation onlyon demand, performs better than proactive routing protocol,which always maintains route to destination by periodicallyupdating, due to its lower control overhead. In [7], SuhuaTANG and Bing ZHAGN propose a local Update schemebased on AOMDV. Hamed EI-Afandi present a simulationstudy between the Ad-hoc protocols IWAR and AODV [8].Huaizhi Li and Mukesh Singhal present a scalable routingprotocol in [9]. It is based on DSR and AODV and performswell in large network. In [10], JeeHyeon Na proposes a novelrouting path discovery and data delivery scheme for ubiquitousinternet connectivity based on hierarchical mobile AODV6network. In [11], AODV is reviewed and implemented in atestbed consisting of some PCs, laptops and PDAs. RendongBai and Mukesh Singhal [12] combine DSR and AODV intoone hierarchical routing protocol (DOA) and present twonovel techiques: one is an efficient loop detection methodand a multitarget route discovery. Obviously, AODV is wellresearched for its advantage.

The AODV approach builds a single loop-free path to eachother node on the network. Kwan-Wu Chin and Darry Lowepresent a multi-rate opportunistic AODV protocol routingprotocol to strengthen its routes by recruiting neighbors ofnodes on the least cost path as support nodes during theroute construction process [13]. And many research showsthat multipath routing achieves in general better performancethan single path routing in dense networks and networks withhigh traffic load. The Ad hoc On-demand Multipath DistanceVector (AOMDV) routing protocol[14] extends AODV to buildand store several paths in the routing table without findingadditional information, so that when one route is broken, itdoes not necessarily result in a new flood of route requestpackets. Instead, the source node can simply select the nextavailable route from its tables. In [15], Georgios Parissidiscompare the network performance of SMR, AOMDV andMAODV .The Multiple Ad hoc On-demand Distance Vector(MAODV) [16] extends AODV to build several disjoint paths.

978-1-4244-3693-4/09/$25.00 ©2009 IEEE

And It is similar to the AODV protocol. The only difference isthe process of RREQ (Route Request) transmitting and RREP(Route Reply) replying. Comparing with SMR and MAODV,AOMDV achieves the better performance in scenarios withhigh node mobility.

The AOMDV protocol has ”route cutoff” problem that somereverse paths would be omitted, and the joint ratio of pathsof AOMDV impacts the transmission rate and the end-to-enddelay. In this paper, we increase 4 bits control information inRREP packet and change the process of RREP replying tosolve the ”route cutoff” problem and choose the path whichhas less joint node. These changes bring much improvementof network performance.

The rest of the paper is organized as follows. In section II,we give the Network Model. In section III, Our LOAOMDVprotocol is explained in detail. Section IV analyzes the per-formance of proposed protocol. Performance evaluation viasimulation is presented in Section V, and section VI concludesthe paper.

II. NETWORK MODEL

Our LOAOMDV routing protocol is built on the basis ofthe following network model. We suppose that the node areall equal and using omni-directional antennas. The communi-cation link between any two nodes are two-way link. If onenode A can receive the message from the other node B, nodeB can receive the message from node A too.

In mobile ad hoc networks, the path may be broken becauseof the node mobility. The two paths are node-disjoint, whichhas no common node. While the two paths are link-disjoint,which could have common node but no common link. Theprobability of path broken is different between the node-disjoint path and the link-disjoint path. We suppose there aretwo path. path1 has n nodes and path2 has m nodes. If thetwo path node-disjoint. The probability that the two path areboth broken can be written by

p0 = p[Pbreak(path1)] ∩ p[Pbreak(path2)]= [1 − (1 − p)n][1 − (1 − p)m] (1)

If path1 and path2 have one common node, the brokenprobability can be written by

p1 = p[Pbreak(path1)] ∩ p[Pbreak(path2)]= [1 − (1 − p)n−1][1 − (1 − p)m−1] + p

(2)

In order to find out the larger broken probability, we performthe calculation

f(p) = p1 − p2 = p − (1 − p)n−1 − (1 − p)m−1+(1 − p)n+m−2 + (1 − p)n + (1 − p)m − (1 − p)n+m (3)

We can prove that f(p) ≥ 0, if and only if p = 0, f(p) = 0.If the two path has two common node, the broken probabilityis p2. We can also prove that p2 ≥ p1 ≥ p0. Therefore we canalways get pk ≥ · · · ≥ p1 ≥ p0 k ≥ 2. So we know thatthe less common node is, the smaller the broken probability is.We should choose the paths which have less common nodes.

Fig. 1. 4 bits control information

Fig. 2. The routing discovery process

III. LOAOMDV

The main objective of our scheme is to find out the omittedreverse path and establish the more disjoint path. We add 4 bitscontrol information in RREP packet and change the processof RREP replying in our LOAOMDV. It is showed in Fig.1.

REV: this bit is used to determine whether there is omittedreverse path.

NUM: these 3 bits represent an integer which is the commonnode number in one path.

A. Revers Path

The routing discovery process of AOMDV is showed inFig.2. The source node S starts the route discovery andbroadcasts a RREQ to the destination node D. When the nodesA and B receive the RREQ broadcasted by the source node S,they first add their own addresses into RREQs as ”Last hop”respectively. In this paper, the RREQ via node A is labeled asRREQ(A), and the RREQ via node B is labeled as RREQ(B).Then they update some information in their own route tableentry to form reverse paths (A-S and B-S). Finally node Abroadcasts RREQ(A) and node B broadcasts RREQ(B). Afternode C receives RREQ(A) and RREQ(B), it will form twolink-disjoint reverse paths (C-A-S) and (C-B-S). Then it willonly broadcast the first received RREQ(A) to others (supposethat RREQ(A) is received first), if it does not have any routeavailable for destination. Otherwise, C will reply an RREPback to source. When node E and F receive RREP(A), theywill respectively form reverse paths (E-C-A-S) and (F-C-A-S).Once destination receives a RREQ, it will reply to it with arouting packet RREP, even if the RREQ has the same ”Lasthop” as previous RREQs. So node D will both reply RREQ(E)(via node E) and RREQ(F) (via node F). RREP is unicasted tosource through reverse path. Then one RREP arrived node Cthrough node E and the other RREP through node F. The firstarrived RREP will choose one nexthop list to be transmitted.The other will use the left nexthop list if the node has the otherreverse path to source, otherwise the RREP will be discarded.

The node C has two disjoint reverse path to source, (C-A-S)and (C-B-S). The two RREP will arrive the node C throughnode A and node B respectively. Then two forward paths (S-A-C-E-D and S-B-C-F-D) will be established. In AOMDV,the intermediate node treat RREP from different neighbor likethe node C. The node C discards RREQ(B), but establishestwo reverse path to the source node S, (C-A-S) and (C-B-S).The node E and F receive RREP (A), and respectively formreverse paths (E-C-A-S) and (F-C-A-S). The destination nodeD receives RREQs which have the same firsthop. If D firstreceives RREQ(A) from E, a reverse path (D-E--A-S) will beset up. When it receives the second RREQ(A) from F, whichcontains the same ”Last hop”, it will not set up the non-disjointreverse path (D-F--A-S). It is obvious that the destination onlyestablished one reverse path to source. In fact, if there aretwo link-disjoint paths with one or more common intermediatenodes between the source and destination, two reverse pathsand two forward paths ought to be formed. To reduce routediscovery latency, it is necessary to find out all of the existinglink-disjoint reverse paths.

Like AOMDV, the destination will only reply the RREQfrom the different neighbor in LOAOMDV. To solve theproblem, we increase one bit information in RREP. We showthe control bit format in Fig.3, and we call the sign areaas REV. The destination node determines whether it has thedifferent firsthop, when it receives a RREQ. If it has, REV=1;if not, REV=0. The source node will receive two differentRREPs. One’s REV is 1, other’s is 0. The source node willknow that one reverse path is omitted, when it receives theRREP whose REV is 0. Then the source node can seed therequest to establish the omitted reverse path. This can usepiggyback. The request is add to the first packet which is thefirst packet sent through the forward path.

As the example shows in Fig.3, the destination node Dreceives RREQ(A) via node E and RREQ(A) via node F.We suppose that RREQ(A) first arrives. The destination nodeD will reply the RREQ(A) via node E with RREP(REV=1)(the firsthop area is node A). Then the node D will replythe RREQ(A) via node F with RREP(REV=0) (because thefirsthop area is also A). When RREP(REV=1) is receivedby the source node S, the forward path (S-A-C-E-D) andthe reverse path (D-E-C-A-S) have established. The sourcenode can start to send packets directly. Differently, whenRREP(REV=0) is received by the source, the request toestablish the omitted reverse path will be added to the firstpacket sent by the forward path (S-B-C-F-D). Then node Fwill modify the firsthop node A of its route entry (F-C-A-S)with B, when it receives the first packet from node C. Thedestination node D will establish the reverse path (D-F--B-S).The problem is solved.

B. Common Node

As we know, the multiple paths are link-disjoint path inAOMDV. There are common intermediate nodes in the pathsfrom source to destination. Because the packet of two pathsmust be transmitted by these common nodes, the transmission

Fig. 3. The routing reply process

Fig. 4. The intermediate node reply process

rate will be restrained. Besides, the common nodes are usedmore than the other node in those paths. It will result thatthe energy consumption is not balanced. Some nodes will dieprematurely.

To solve this problem, we add the new choosing schemein LOAOMDV. If there are some nodes or some paths de-crease the ratio of joint, the choosing scheme will choosethem. We present the choosing scheme with an example. Asshowed in Fig.4, the node B will receive two RREPs. One isRREP(REV=0) via node C, the other one is RREP(REV=1)via node H. Suppose that RREP(REV=0) via node C firstarrived. Then node B establishes the forward path (B-C--D).After then node B receives RREP(REV=1) via node H, it willdiscard the RREP, because node B don’t have other route entryto source S. We add NUM to RREP. In this area, the numberof common nodes will be recorded. If one node rebroadcaststwo RREPs, the NUM in the second RREP will be increase 1.It is obvious that the NUM of RREP(REV=0) via node C is 1,while that of RREP(REV=1) via node H is 0. The RREP whichhas smaller NUM will be chosen. Then node B will update itsroute entry, when receiving RREP(REV=1,NUM=0) via nodeH. The forward path (B-H--D) will be chosen.

Specially, we only use 3 bits control information, but wefind the better path. It will be a great contribution to thenetwork performances. But it is different to the disjoint path inMAODV. In MAODV, every node only transmits one RREQpacket in order to build disjoint paths. The number of pathwill be very few and it is the just reason that MAODVdon’t perform well in high mobility scenarios. Differently,LOAOMDV find that the disjoint paths which exits but notbe established. So it can also perform well in scenarios withhigh node mobility as AOMDV.

Finally, we make a summary of our LOAOMDV algo-rithm. We add 4 bits information in RREP packet, REV

Fig. 5. The Destination reply process

Fig. 6. The process of intermediate node

and NUM. The destination node receiving RREQ packetsgenerates RREP packets toward the source node by unicast.The first arriving RREQ packet is unconditionally acceptedand a RREP(REV=1) is immediately generated to create aprimary route, which is equal to the AOMDV. Delayed RREQpackets are conditionally accepted according to the specialmetric. To the RREQs which is from different neighbor nodes,the destination node determines whether it has the differentfirsthop, when it receives a RREQ. If it has, REV=1; if not,REV=0. This information is provided to the source nodewhich can be establish the omitted reverse node. The otherwork of the destination node is to initialize NUM to 0. Theintermediate node received RREPs choose and update the routeentry according to NUM. The route entry with smaller NUMwill be choose and activated. The procedure of the destinationnode replying process is shown in Fig.5, and the procedure ofthe intermediate node broadcasting process is shown in Fig.6.

Fig. 7. Two nodes Scenario

IV. PERFORMANCE ANALYSIS

Considered a wireless ad hoc network with n mobile nodes,which are uniformly distributed in a field with a size of a× bsquare meters. The wireless transmission range of node is rmeters. Dimensions of the network are a and b meter wherea, b � r. Fig.9 shows a simple scenario with node A and nodeB. We refer to the area that is covered by the transmissionrange of nodes A and nodes B as SA and SA respectively.The common neighbor nodes will be located in the area ofSA ∩ SB . If we consider D as the distance between node Aand node B, the intersection area of SA and SA can be writtenby

INTC(A,B) = 4∫ r

D2

√r2 − x2dx (4)

Since the location of node B is random inside node A’stransmission reage, the average value can be obtained byintegrating the above value over the circle of radius x centeredat node A for x in area SA ∩ SB ,

E[INTC(A,B)] =∫ r

0

2πx · INTC(A,B)dx

πr2≈ 0.59πr2

(5)The location of node A can be considered anywhere in thefield. We can calculate the probability that an arbitrary nodeB is located in the wireless transmission range of node A isp, and it is given by

p = πr2/ab (6)

Therefor we can write the average number of nodes in areaSA ∩ SB as

E[num] = 0.59πr2(n − 2)/ab = 0.59p(n − 2) (7)

In the case like Fig.2, there will be some omitted reverse path.In the case like Fig.4, some better path may not be established.In case 1 and case 2, our LOAOMDV can improve networkperformance greatly. In Fig.10, we give the probability oftwo case in two typical scenarios. Then we will evaluate theLOAOMDV in this two scenarios. We give the frame structureRREP in Fig.11.

Type: 8 bitsJ: 1 bitR: 1 bit

Fig. 9. Frame structure of RREP .

Fig. 8. Probability of two case1 and case2

G: 1 bitD: 1 bitU: 1 bitReserved: 11 bitsAdvertised hopcount: 8 bitsOur LOAOMDV only uses 4 bits. The control information

format is showed in Fig.1.

V. SIMULATION RESULTS

In this subsection we evaluate the performance of AOMDVand LOAOMDV protocol and compare them. We use a de-tailed simulation model based on ns-2. Simulation environ-ment is as follows:

Propagation: TwoRayGroundRadio range of a node: 250mChannel capacity: 2Mb/secMedium Access Control (MAC) protocol: IEEE 820.11Distributed Coordination Function (DCF) The node move-

ment model we use is the random waypoint model [17]. Thesimulation time is 900 seconds while the max speed variesfrom 0m/s (no mobility) to 30m/s. Nodes move with a speed,uniformly distributed in the range [0,max speed].

We consider 2 network sizes with 50 nodes in a rectangularfield of size 1500m×300m and 100 nodes in a rectangularfield of size 2200×600m. This two scenarios are widely usedin simulations. Other settings are designed as follow:

Simulation area: 1500 m×300 mSize of data packet: 512bytesData rate: 4 packet/secNumber of nodes: 50

Fig. 10. Packet delivery ratio

Fig. 11. Average end-to-end delay

Simulation area: 2200 m×600 mSize of data packet: 512bytesData rate: 4 packet/secNumber of nodes: 100Network interface queue size: 64We have evaluated three important performance metrics:

packet delivery ratio, average end-to-end delay and normalizedroute load.

Packet delivery ratio is the ratio of the total number ofdelivered data packets at the destination to the total numberof data packets sent. In Fig.10, we plot the packet deliveryratio in two different scenarios. We fixed the pause time to 0seconds. By increasing the node max speed, we see that theperformance decreases. It’s obvious that the packet deliveryratio of LOAOMDV is higher than that of AOMDV. The

Fig. 12. Normalized routing overhead

reason is very obvious. The omitted path is established. Thetwo paths have few common nodes. So the route discoveringfrequency will decrease. Of course, the packet delivery ratiowill increase.

Average end-to-end delay is the transmission delay of datapackets that are delivered successfully. This delay consists ofpropagation delays, queuing delays at interfaces, retransmis-sion delays at the MAC layer, as well as buffering delaysduring route discovery. Fig.11 show the average end-to-enddelay in the two scenarios. By the node max speed increasing,the average end-to-end delay increases. Obviously, the averageend-to-end delay of LOAOMDV is lower than that of AOMDV.Because of the establishing of the omitted path and the disjointpath, the backup route of LOAOMDV is more than that ofAOMDV.

Normalized routing load is the total number of routingpackets transmitted for each delivered data packet. In Fig.12,we give the comparison of the normalized routing overheadin the two scenarios. By the node’s speed increasing, thenormalized routing overhead increases very obviously. We use4 bits control information of RREP packet. It is just 4 bits.As the route discovery frequency decreases, the total numberof RREQ packets, RREP packets and RRER packets will belower than that of AOMDV. So the decreasing of routingoverhead is not difficult to understand.

VI. CONCLUSION

The objective of the present paper is present a LOAOMDVrouting protocol based on AOMDV. Compared with AOMDV,we add two sign area to RREP in LOAOMDV. The newprotocol can find the omitted reverse path and choose the betterpath first if there is some path having fewer common nodes.The changing improves the network performance obviously.Simulation show LOAOMDV has lower routing overhead.Average end-to-end delay and packet delivery ratio also haveimproved. And the LOAOMDV routing protocol is performwell in highly dynamic and high mobility ad hoc networks.Finally, we will begin implementation of the protocol onnotebook computers and continue do research on multipathrouting protocol.

ACKNOWLEDGMENT

The paper is supported by National Hi-Tech Research andDevelopment Plan of China under Grant 2006AA01Z262, itis also supported by National Key Laboratory Foundation ofChina under Grant 9140C5303010703 and National NaturalScience Foundation of China 60832007.

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