Routing and Security in Mobile Ad Hoc Networks

A Mobile Ad hoc Network (MANET) consists of a set of nodes which can form a network among themselves. MANETs have applications in areas such as military, disaster rescue operations, monitoring animal habitats, etc. where establishing fixed communication infrastructure is not feasible. Routing protocols designed for MANETs can be broadly classified as position-based (geographic), topology-based and hybrid. Geographic routing uses location information of nodes to route messages. Topology-based routing uses network state information for route discovery and maintenance. Hybrid routing protocols use features in both position-based and topology-based approaches. Position-based routing protocols route packets towards the destination using greedy forwarding (i.e., an intermediate node forwards packets to a neighbor that is closer to the destination than itself). If a node has no neighbor that is closer to the destination than itself, greedy forwarding fails. In this case, we say there is void. Different position-based routing protocols use different methods for dealing with voids. Topology-based routing protocols can be classified into on-demand (reactive) routing protocols and proactive routing protocols. Generally, on-demand routing protocols establish routes when needed by flooding route requests throughout the entire network, which is not a scalable approach. Reactive routing protocols try to maintain routes between every pair of nodes by periodically exchanging messages with each other which is not a scalable approach also. This thesis addresses some of these issues and makes the following contribution. First, we present a position-based routing protocol called Greedy Routing Protocol with Backtracking (GRB) which uses a simple backtracking technique to route around voids, unlike existing position-based routing protocols which construct planarized graph of the local network to route around voids. We compare the performance of our protocol with the well known Greedy Perimeter Stateless Routing (GPSR) protocol and the Ad-Hoc On-demand Distance Vector (AODV) routing protocol as well as the Dynamic Source Routing (DSR) protocol. Performance evaluation shows that our protocol has less control overhead than those of DSR, AODV, and GPSR. Performance evaluation also shows that our protocol has a higher packet-delivery ratio, lower end-to-end delay, and less hop count, on average, compared to AODV, DSR and GPSR. We then present an on-demand routing protocol called ``Hybrid On-demand Greedy Routing Protocol with Backtracking for Mobile Ad-Hoc Networks which uses greedy approach for route discovery. This prevents flooding route requests, unlike the existing on-demand routing protocols. This approach also helps in finding routes that have lower hop counts than AODV and DSR. Our performance evaluation confirms that our protocol performs better than AODV and DSR, on average, with respect to hop count, packet-delivery ratio and control overhead. In MANETs, all nodes need to cooperate to establish routes. Establishing secure and valid routes in the presence of adversaries is a challenge in MANETs. Some of the well-known source routing protocols presented in the literature (e.g., Ariadne and endairA) which claim to establish secure routes are susceptible to hidden channel attacks. We address this issue and present a secure routing protocol called SAriadne, based on sanitizable signatures. We show that our protocol detects and prevents hidden channel attacks

An evaluation of the performance of a NoSQL document database in a simulation of a large scale Electronic Health Record (EHR) system

Electronic Healthcare Record (EHR) systems can provide significant benefits by improving the effectiveness of healthcare systems. Research and industry projects focusing on storing healthcare information in NoSQL databases has been triggered by practical experience demonstrating that a relational database approach to managing healthcare records has become a bottleneck. Previous studies show that NoSQL databases based on consistency, availability and partition tolerance (CAP) theorem have significant advantages over relational databases such as easy and automatic scaling, better performance and high availability. However, there is limited empirical research that has evaluated the suitability of NoSQL databases for managing EHRs. This research addressed this identified research problem and gap in the literature by investigating the following general research: How can a simulation of a large EHR system be developed so that the performance of NoSQL document databases comparative to relational databases can be evaluated? Using a Design Science approach informed by a pragmatic worldview, a number of IT artefacts were developed to enable an evaluation of performance of a NoSQL document oriented database comparative to a relational database in a simulation of a large scale EHR system. These were healthcare data models (NoSQL document database, relational database) for the Australian Healthcare context, a random healthcare data generator and a prototype EHR system. The performance of a NoSQL document database (Couchbase) was evaluated comparative to a relational database (MySQL) in terms database operations (insert, update, delete of EHRs), scalability, EHR sharing and data analysis (complex querying) capabilities in a simulation of a large scale EHR system, constructed in the cloud environment of Amazon Web Services (AWS). Test scenarios consisted of a number of different configurations ranging from 1, 2, 4, 8 and 16 nodes for 1Million, 10 Million, 100 Million and 500 Million records to simulate database operations in a large scale and distributed EHR system environment. The Couchbase NoSQL document database was found to perform significantly better than the MySQL relational database in most of the test cases in terms of database operations -insert, update, delete of EHRs, scalability and EHR sharing. However, the MySQL relational database was found to perform significantly better than the Couchbase NoSQL document database for the complex query test that demonstrates basic analysis capabilities. Furthermore, the Couchbase NoSQL document database used significantly more disk space than the MySQL relational database to store the same number of EHRs. This research made a number of important contributions to knowledge, theory and practice. The main theoretical contribution to design theory was the design and evaluation of a prototype EHR system for simulating database management operations in a large scale EHR system environment. The prototype EHR system was underpinned by the development of two data models with data structures designed for a NoSQL document database and a relational database and a random healthcare data generator which were based on Australian Healthcare data characteristics and statistics. The design of a data model for EHRs for a NoSQL document database using an aggregated document modelling approach provided an important contribution to data modelling theory for NoSQL document databases using de-normalisation and document aggregation. The design of a random healthcare data generator was another important contribution to design theory and was based on a data distribution algorithm (multinomial distribution and probability theory) informed by National Health Data Dictionary and published Australian Healthcare statistics. The prototype EHR system allowed this study to demonstrate through a simulated performance evaluation that a NoSQL document database has significant and proven performance advantages over relational databases in most of the database management test cases. Hence this study demonstrated the utility and efficacy of a NoSQL document database in the simulation of a large scale EHR system. This research has made a number of important contributions to practice. Foremost is that the IT artefacts (namely, a data model for storing EHRs in a NoSQL document database, a random healthcare data generator and a prototype EHR system) developed and evaluated in this research can be readily adopted by practitioners. Another important practical contribution of this research is that it is based on the open source availability of NoSQL database and relational database alternatives. Hence, this research can provide a sound basis for lower-income countries as well higher-income countries to establish their own cost-effective national EHR systems without the restrictions, limitations, complexity or complications of similar proprietary relational database systems