QUALITY OF SERVICE ROUTING AND GATEWAY DISCOVERY IN MOBILE AD HOC NETWORKS

Abstract

A mobile ad hoc network (MANET) is a collection of mobile nodes that can communicate with each other using multi hop wireless links without utilizing any fixed base station infrastructure and centralized management. The field of mobile ad hoc networks has gained significant interest among researchers in recent years because of their ease of deployment. It is easy and inexpensive to build such networks as no infrastructure other than mobile devices is needed. Two of the major challenges that need to be addressed in order to realize the practical benefits of ad hoc networks are: providing distributed quality of service (QoS) guarantees and multi-hop Internet access. Quality of Service can be defined as the ability of the network to offer required service demanded by a particular application and can be achieved by establishing some type of control over certain network parameters. Different network applications have different demands on the network, such as delay, jitter, bandwidth, reliability etc. It is very challenging to provide QoS in wireless ad hoc networks due to the intrinsic properties of this kind of networks, e.g., variable capacity, dynamic topology, etc. Delay raises much more QoS issues with applications like voice, video and fax transmission. Nowadays, Internet accessing users are also rapidly growing and the Internet itself has become a mass media. Therefore, many MANET users may also want to access Internet services in addition to communicating among themselves. Mobile ad hoc networks are considered complementary to IP networks in a sense that Internet connectivity can be extended into the ad hoc networks making them part of the Internet. While there has been a lot of work on ad hoc routing protocols to date, little attention has been given to the discovery of Internet gateways between ad hoc networks and the Internet. When a mobile node in an ad hoc network wants to access the Internet, it should first connect to an appropriate Internet gateway that provides the Internet connectivity for it. Therefore, we need an efficient Internet gateway discovery and selection mechanism for Internet access through mobile nodes from ad hoc domain. The work presented in this thesis is an effort to address these issues by proposing new and efficient approaches. First part of the thesis proposes an on demand delay based Quality of Service (QoS) routing protocol to ensure that delay does not exceed a maximum value for each session between a pair of source and destination. Performance evaluation of AODV and DSR

protocols in different scenarios was analyzed using GloMoSim simulator. Moreover, many QoS routing protocols designed are extension ofAODV protocol. Considering these facts, we propose an extension of AODV routing protocol for delay sensitive applications in mobile ad hoc networks, which we call AODV-D. Delay aware routing protocols make path selection between source and destination based on the delay over the discovered links during route discovery. However, most of these protocols do not take MAC contention delay during route discovery process. The proposed protocol computes node delay dynamically and selects routes with least traffic and follows alternate route method for route maintenance. The performance of this protocol has been compared against original best-effort AODV and QoS-AODV protocols through simulation. Performance of the proposed algorithm has been evaluated by taking different mobility and traffic patterns and is found to be performing well. The result of the proposed QoS routing protocol was also analytically verified. The second part of the thesis analyzes three Internet gateway discovery protocols. Several Internet gateway discovery protocols for interconnectivity between mobile ad hoc networks and Internet have been proposed in the literature. However, a comprehensive performance evaluation and comparative analysis of these methods have not been performed yet. Thus, evaluation and performance comparison of Internet gateway discovery methods in different scenarios enables one to design and choose a proper Internet gateway discovery protocol. It sheds some light onto the performance implications of the main features of each approach, presenting simulation results, which provide valuable information to MANET-Internet protocol designers. The performance of three gateway discovery algorithms (reactive, proactive and hybrid) in terms of performance metrics throughput, end-to-end delay, jitter and packet loss using NS2 has been analyzed. As a result of our finding, we reach at the conclusion that at lighttraffic load/low mobility, the performance of proactive and hybrid gateway discovery is better as compared to reactive discovery. These approaches result higher throughput, lower end-to-end delay and packet loss comparedto reactive. But with increase in number of sources and traffic rate, the reactive gateway discovery outperforms proactive and gives similar performance with hybrid discovery approach. However, gateway discovery overhead increases in case of reactive approach with increase in number of sources connecting to the Internet. The performance of hybrid gateway discovery always remains in between reactive and proactive approaches. We also compare the routing overheads obtained through our simulation with routing overhead computed analytically in the same scenario by Ruiz et al. for the three Internet gateway discovery approaches. The third part of the thesis first analyzes existing load-aware routing protocols in MANETs and based on this analysis proposes an efficient Internet gateway discovery protocol for MANET-Internet integration. Most Internet gateway discovery approaches use minimum hop path for Internet gateway selection. However, a minimum hop path may not always be efficient if some of the nodes along the path have long interface queues of waiting packets. Thus, the focus of this part is to devise and evaluate a proactive loadaware Internet gateway discovery approach that takes into account size of interface queue in addition to the traditional minimum hop metric to efficiently select an Internet gateway for MANET-Internet connectivity. For selection of a particular Internet gateway by a mobile node, we propose modification in the Internet gateway advertisement message, which is periodically broadcasted in the MANET domain and also in the routing table maintained at each mobile node. We introduce an additional metric called gateway_adv_queue, which takes into account the effect of interface queue occupancy level along a route. An additional field rt_qlen_metric is used to record the effect of this metric along a route to the Internet gateway in routing table of each mobile node. Our approach also allows an efficient handoff from one Internet gateway to another and still maintains a seamless connectivity to a fixed host. The impact of this combined metric on the Internet gateway discovery performance is investigated. Performance improvement was observed in the throughput and average end-to-end delay of a mobile node in the proposed protocol, in comparison to existing approach as traffic/mobility increases. To summarize, the thesis proposes a new delay based routing method for MANET, presents simulation analysis of various Internet gateway discovery approaches and proposes a new method for Internet gateway discovery for MANET-Internet integration. The simulation results show that the methods/protocols proposed in this thesis improve the performance of ad hoc networks as well as wired-MANET interconnectivity significantly. Lastly, the contributions made in the thesis in the area of QoS routing and MANET Internet integration have been summarized and scope for future work is outlined.