The Study Of An On-Demand Hybrid Multipath Routing Protocol And Its Impact On TCP Performance

Ad Hoc Networks are formed with mobile hosts(MHs).They can dynamically create a wireless network among themselves without the aid of any infrastructure.Every mobile host(MH)can move arbitrarily and communicate with each other by using multi-hop wireless technology. Each mobile host also acts as a router and forwards data packets to nearby mobile hosts.Due to the dynamic nature of the network topology and resource constraints,designing an efficient routing in MANETs is challenging.To tolerate communication faults,this study explores the network redundancy through multipath routing.The proposed On-demand Hybrid Multipath Routing version 2(OHMRv2)which is the extension of the On-demand Hybrid Multipath Routing(OHMR)proposed by Chuan-Ching Sue and Ren-Jie Chou in[23].OHMRv2 is based on AODV and uses the source routing technique to create multiple paths like OHMR.And it features a novel characteristic;it incorporates the braided multipath classification in his route selection method.That means, OHMRv2 can discover the braided multipath with two paths of equal length and braided multipath with two paths of different lengths.Through simulations results,it has been shown that under high mobility scenario,OHMRv2 can reduce the frequency of route discoveries,can maintain an end-to end transmission for a longer period than other multipath routing schemes and achieve a higher packet delivery ratio.Another result is that under high mobility scenario and when the number of nodes is less than 90,the braided multipath with two paths of equal length has the low frequency of route discovery than the braided multipath with two paths of different lengths. The second part of this thesis investigates TCP performance over OHMRv2.Multipath routing can improve the path availability in mobile environment.Thus,it has a great potential to improve TCP performance in ad hoc networks under mobility.When TCP is used,it has been found that generally using multiple paths simultaneously may actually degrade TCP performance.This is due partly to frequent out of order packet delivery via different paths.Based on that,another multipath strategy called backup routing has been tested.Through simulation results,it has been demonstrate that under the backup routing scheme,TCP is able to gain improvements against mobility.Some important results are reported in Chapter 5 and simulation results showed that by careful selection of the multipath routing strategies,it is possible to improve TCP performance when the network traffic is heavy.