A Hybrid Multipath Routing in Mobile ad hoc Networks

Chuan-Ching Sue and Ren-Jie ChiouDepartment of Computer Science and Information Engineering,

National Cheng Kung University, Tainan, TaiwanTel: 886-6-2757575 ext. 62543

Fax: 886-6-2747076suecc@mail.ncku.edu.tw

Abstract

Due to the dynamic nature of the network topologyand resource constraints, designing an efficientrouting in MANETs is challenging. To toleratecommunication faults, this study explores the networkredundancy through multipath routing. The designatedon-demand hybrid multipath routing (OHMR) featurestwo novel characteristics; it establishes multiple node-disjoint and braided routing paths between a source-destination pair and it maintains an end-to-endtransmission for a longer period than other multipathrouting schemes. Through simulation results, we showOHMR can reduce the frequency of route discoveriesand achieve a higher packet delivery ratio.

1. Introduction

Multipath routings which can toleratecommunication faults establish multiple paths betweena source and a destination. In these protocols, a newroute discovery operation is invoked only when all ofthe routing paths in the network fail. Multipath routinghas been proposed for ad hoc networks such asMANETs [2, 3, 4, 5]. Although multipath protocolsbuild multiple routes, the majority of them establishonly node-disjoint multipath or braided multipath.

This paper proposes a novel and practical routingprotocol designated On-demand Hybrid MultipathRouting (OHMR). This protocol modifies and extendsAODV [1] to identify hybrid multipath comprisingmultiple node-disjoint and braided routing paths. Thefundamental design principle of OHMR is to decrease

the impact of communication faults and then reduce theflooding frequency. Through simulation results, weshow OHMR can reduce the frequency of routediscoveries and achieve a higher packet delivery ratio.

2. Proposed Method

These braided alternate paths would expend energycomparable to the primary path. OHMR also discovermultiple node-disjoint paths. Because the lowrelationship between the primary path and node-disjoint alternate paths, node faults on them do notaffect each other. The resulting set of paths (includingthe primary path) is designated as the hybrid multipath.

2.1. Route Record

OHMR extends AODV to record the path in RREQpackets. When the RREQ packets are generated orforwarded by the nodes in the network, each nodeappends its address to the routing request packets.

2.2. RREQ Propagation

The source broadcasts a RREQ to its neighbors,which then forwards the request to their neighbors, andso on, until either the destination or an intermediatenode with a route to the destination. Notably, thepacket forwarding approach of OHMR is differentfrom AODV. In the approach of OHMR intermediatenodes forward the duplicate packets that traversedthrough two different neighbors. The approach enablesus to discover both braided and node-disjoint paths.

2.3. Route Selection MethodThe author is with the Department of Computer Science andInformation Engineering, National Cheng Kung University,Taiwan, R.O.C. This research was supported by the NationalScience Council, Taiwan, R.O.C., under Grant NSC95-2221-E-006-093-MY2.

12th Pacific Rim International Symposium on Dependable Computing (PRDC'06)0-7695-2724-8/06 $20.00 © 2006

The destination is responsible for selecting multiplebraided and node-disjoint route paths. When receivingthe first RREQ, the destination records the list of nodesin RREQ and it is copied to a RREP and sends theRREP to the source via the list of nodes. When thedestination receives a duplicate RREQ, it will comparethe list of node in the RREQ to that in routing table. Ifonly source node and destination node are the samebetween them, the path is node-disjoint with theprimary path. If one of the nodes in the list of nodes inthe routing table is not in list of nodes in the RREQ, thepath is a braided path. Otherwise, the received RREQis discarded.

3. Simulation Results

Our simulations use ns-2. Simulation modeled anetwork with 50 mobile nodes placed randomly in arectangular field, 1500mx300m area. Each run isexecuted for 300 seconds of simulation time. Wevaried the pause time to simulate different mobilitydegrees. The minimum and the maximum speed werezero and 20 m/s. During the simulation period, CBRtraffic will be generated randomly. CBR uses UDP asits transport protocol. There were ten data sessions,each with the traffic rate of four packets per second.

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Figure 1: Route discovery frequency.Figure 1 shows the result of frequency of routing

discovery versus the pause time. The frequency ofrouting discovery for OHMR is the lowest comparedwith node-disjoint multipath and braided multipathsince OHMR uses hybrid multipath to maintains anend-to-end transmission for a longer period than singlepath routing, braided and node-disjoint multipathrouting. The average packet delivery ratio is shown inFigure 2. OHMR lost fewer packets than AODV,braided multipath and node-disjoint multipath. This isdue to the fact that the route discovery frequency forOHMR is smaller among other routing schemes.Therefore, OHMR has the lowest packet delivery ratioamong other schemes irrespective of various pause

times. It is obvious that OHMR provide efficient faulttolerance and efficient recovery from failures resultingfrom node movement in MANETs.

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Figure 2: Packet delivery ratio.

4. Conclusions

This study has proposed a multipath extension to theAODV on-demand routing protocol. The proposedOHMR protocol searches for node-disjoint and braidedroutes using a single flooding query in order to providesufficient redundancy. The key advantage of theproposed approach is a significant reduction in thefrequency of route discovery flooding. Simulationresults show that OHMR can reduce the frequency ofroute discovery and increase packets delivery ratio. In afuture study, OHMR will be extended to distributetraffic with load balance.

5. References

[1] E. Perkings, E. M. Belding-Royer and S. R. Das, “AdHoc On-Demand Distance Vector (AODV) Routing”,http://www.ietf.org/rfc/rfc3561.txt, IETF RFC, July 2003.

[2] B. Ganesan, R. Govindan, S. Shenker, and D. Estrin,“Highly-Resilient, Energy-Efficient Multipath Routing inWireless Sensor Networks”, Mobile Computing andCommunications Review (MC2R), Vol. 4, no. 5, October2001.

[3] S.J. Lee and M. Gerla, “Split Multipath Routing with Maximally Disjoint Paths in Ad Hoc Networks”, In Proc. ofthe IEEE ICC, vol. 10, 11-14 June 2001, pp. 3201-3205.

[4] A. Nasipuri, R. Castaneda, and S. R. Das, “Performance of Multipath Routing for On-demand protocols in Mobile AdHoc Networks”, ACM Mobile Networks and Applications(MONET), Vol. 6, Issue 4, August 2001, pp. 339-349.

[5] M. K. Marina, and S. R. Das, “On-demand MultipathDistance Vector Routing in Ad Hoc Networks”, IEEEInternational Conference on Network Protocols (ICNP),November 2001, pp. 14-23.

12th Pacific Rim International Symposium on Dependable Computing (PRDC'06)0-7695-2724-8/06 $20.00 © 2006