With the rapid development of the Internet, new theories and technologies are blooming and boosting the associated applications. One group of important applications is the multiparty multimedia communications. Satellites, which have played an important role in telephony communication and TV broadcasting services, could also play an important role to provide multiparty multimedia communications with their global coverage and on-board processing ability over IP networks. IP multiparty multimedia conferencing is one of these communication applications. With the support of satellites, one can provide an IP conferencing service globally to anywhere, even the place does not have the access to terrestrial networks. This thesis introduces the VoIP technologies that underpin IP conferencing services. It describes protocols, architectures, network entities, and network performance. In addition, this thesis presents how a multicast routing architecture was designed for an IP conferencing system with consideration to the new features introduced by an integrated GEO satellite network. An associated conferencing model will be presented as well to accompany this routing architecture. All of the technologies used in the design were implemented in a demonstrator. To test and evaluate the system, efforts have been put into the IP traffic measurement technologies and a measurement regime was developed to evaluate the system with consideration to multicast routing and the system architecture. New relative QoS requirements of multiparty communications are identified in this thesis. A set of parameters to present these new requirements are proposed as derivations of the IPPM (IP Performance Metrics) end-to-end parameters. A new adaptive QoS optimisation algorithm is proposed that is based on the measurement of these new parameters to satisfy the relative QoS requirements of the multiparty multimedia communications. Simulations were carried out to verify this algorithm and the results prove that it can optimize the relative QoS for multiparty multimedia communications.

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The fast growth and development of wireless computer networks and multimedia applications means it is essential that these applications can be transmitted over the standard IEEE 802.11 Medium Access Control (MAC) protocol with high Quality of Service (QoS). The lack of QoS in the standard IEEE 802.11 Distributed Coordination Function (DCF) results in applications with considerably different QoS requirements receiving similar network services. This means, the performance of time-sensitive applications with stringent delay, jitter, and packet loss requirements will not be met. Even time-insensitive applications will be treated unfairly because access to the medium is on a random basis. Therefore, the main aims of this thesis are: (i) to investigate the limitations and performance of the IEEE 802.11 DCF, (ii) to develop a comprehensive solution that provides effective and efficient QoS provisioning in IEEE 802.11 DCF scheme in a fair, scalable, and robust manner. The latter is achieved by developing novel MAC mechanisms for providing QoS in the IEEE 802.11 DCF for multimedia transmission. The scarcity of channel capacity, unfairness and hidden terminal problems, multiple hops, and other conditions and parameters that affect QoS in a wireless network are issues which require in depth investigations and analysis. In this thesis, extensive investigations using the network simulator 2 (NS-2) package were carried out to examine the impact of these issues on the main QoS parameters (throughput, delay, jitter, packet loss and collision). The findings revealed that the IEEE 802.11 DCF protocol performed inadequately when transmitting various applications due to the limitations inherent in its operation. The performance of the IEEE 802.11 DCF protocol was also investigated by studying the impact of varying the values of minimum Contention Window (CW[min]) and the Distributed Inter Frame Space (DIFS). The study shows that inappropriate values of CW[min] and DIFS resulted in significant network performance degradations and demonstrated that it was important to select an appropriate set of MAC protocol transmission parameters in order to provide improved QoS.Artificial Intelligence (AI) techniques using fuzzy logic and Genetic Algorithms (GAs) for assessing and optimising MAC protocol transmission parameters were developed and their effectiveness evaluated. The study confirmed that the application of AI techniques significantly improved the QoS for audio and video applications by more than 50% and fairly shared the channel access among the contending stations as compared to the standard IEEE 802.11 DCF scheme. Ratio based and Collision Rate Variation (CRV) schemes were developed to dynamically adjust the CW and DIFS values according to the current and past network conditions. Using these schemes significant improvements with service differentiation were achieved in an Independent Basic Service Set (IBSS). A queue status monitoring technique was devised for the intermediate stations. This provided QoS differentiation at the MAC layer for multi-hop networks. Autoregressive (AR) models that accurately predicted the network parameters were also developed. These enabled the MAC protocol transmission parameters to be adjusted in an improved manner. Using these models, average QoS was improved by more than 60%; average delay, packet loss and collision were reduced by more than 50% compared to IEEE 802.11 DCF scheme. This led to the development of novel MAC mechanisms to provide QoS in IEEE 802.11 MAC protocol. The mechanisms support multiple QoS metrics and consider traffic history and predict future network conditions. The schemes also are characterised by the simplicity, robustness, and ease of implementation. The contribution of this thesis is the development of a comprehensive solution to provide effective and efficient QoS differentiation in IEEE 802.11 DCF scheme for multimedia transmission in a distributed, fair, scalable, and robust manner. Furthermore, through the use of these approaches, the findings of this study provide a framework that also contributes to the knowledge concerning the QoS over the IEEE 802.11 MAC protocol.

Since the first generation of mobile communication systems (IG), mobile services have been relying on ground-based infrastructures. However, the increasing mobile services demand on higher frequencies and higher data rates has been urging the ground-based systems to have far more sites. With a limited number of appropriate sites, achieving seamless coverage and supporting high user mobility may not be cost effective. On the other hand, satellites have been operated to gain regional or global mobile communications coverage and offer high user mobility. Yet these space-based infrastructures have high latency (i.e. propagation delays) and propagation loss that substantially limit the system capacity and make the user terminals expensive. Hence, for about a decade, aerial platforms have been studied and recognised as potential sky-based infrastructures as part of the future mobile communications. In the year 2000, High Altitude Platform Station (HAPS) has been accepted as an alternative infrastructure for the third generation of mobile communication systems (3G) such as UMTS. However, most of the attention is currently more towards the development of sophisticated platform technologies that have long endurance and capable of offering high system capacity. Consequently, the implementation and desperately required proof of the concept are significantly delayed. Furthermore, many studies have covered the exploitation of the strength of aerial platforms but none has comprehensively addressed the challenging properties of such platforms. Therefore, instead of waiting for the maturity of the platform technologies to fit with the mobile communications requirements, in this work airplane (an existing aerial platform) is selected as infrastructure for UMTS. Apart from the maturity of the airplane technology and the ultra-fast deployment features for emergency situations, airplanes also resemble the most challenging features of aerial platforms that are also addressed in this thesis. Severe atmospheric disturbance, high airplane speed, and short endurance are identified as the main features of Airplane UMTS. These features are realistically incorporated into an Airplane UMTS system level simulator, which is developed for the study of the characteristics and performance of the system in terms of Doppler, coverage, interference, coexistence with ground-based system, and airplane handover. The results show that the viability of Airplane UMTS is very encouraging. The Doppler rates are less than the ones of the benchmark system, ground-based UMTS, although the Doppler shifts are higher due to the mobility of the airplane. The airplane attitude does not have significant effects to the system coverage but it does affect the handover performance particularly for a system with fixed mounted multibeams antenna. The overall interference in the system is also affected by the airplane mobility, but it is still better than the ground-based system. Airplane UMTS can also coexist very well with the ground-based UMTS as a neighbouring or even as an overlay system. The short endurance problem can be overcome by the implementation of the proposed smooth airplane handover technique.

It has been observed that the current best-effort IP packet delivery service in the global Internet is sometimes not good enough for emerging real-time multimedia applications. These resource intensive applications normally have more stringent requirements on bandwidth, delay, delay jitter etc. The quality of service (QoS) requirements of these applications raise new challenges for the development of new routing mechanisms. QoS routing can provide increased network utilisation compared to best-effort routing by efficiently regulating and managing resource sharing across a network. However, the benefit of QoS routing comes with complex routing computation costs and increased routing protocol overhead. It is impractical to collect detailed global state information and keep it up-to-date in large-scale dynamic networks, such as the Internet. As a result, inaccurate link-state information increases the flow blocking probability and makes source nodes select non-optimal paths. To maximise the link utilisation and meet application QoS requirements, routing algorithms need accurate link-state information to make routing decisions. This thesis investigates the statistical properties of time series of link utilisation. In particular, the evaluation focuses on the presence of autocorrelation in the time series. Further study under various link-state update policies, network and traffic configurations identifies the factors that may affect the statistical properties of the time series. Based on this analysis, a prediction-based link-state update policy is proposed to reduce the effect of inaccurate link-state information. The approach predicts the link-state utilisation trend based on past values. By advertising trend rather than instantaneous link utilisation, the routing algorithms may have more valuable information to make routing decisions instead of being affected by short lived sudden changes. An appropriate model that can satisfactorily fit the actual model is identified, estimated and validated. Finally, the performance of the proposed prediction-based link-state update policy is validated by simulation and compared with conventional update policies under a variety of network configurations. the results show that this approach is effective in improving routing performance.

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A Mobile Ad Hoc Networks (MANET) is a collection of mobile nodes that can communicate with each other using multihop wireless links without utilizing any fixed based-station infrastructure and centralized management. Each mobile node in the network acts as both a host generating flows or being destination of flows and a router forwarding flows directed to other nodes. Future applications of MANETs are expected to be based on all-IP architecture and be capable of carrying multitude real-time multimedia applications such as voice and video as well as data. It is very necessary for MANETs to have an efficient routing and quality of service (QoS) mechanism to support diverse applications. This thesis proposes an on-demand Node-Disjoint Multipath Routing protocol (NDMR) with low broadcast redundancy. Multipath routing allows the establishment of multiple paths between a single source and single destination node. It is also beneficial to avoid traffic congestion and frequent link breaks in communication because of the mobility of nodes. The important components of the protocol, such as path accumulation, decreasing routing overhead and selecting node-disjoint paths, are explained. Because the new protocol significantly reduces the total number of Route Request packets, this results in an increased delivery ratio, smaller end-to-end delays for data packets, lower control overhead and fewer collisions of packets. Although NDMR provides node-disjoint multipath routing with low route overhead in MANETs, it is only a best-effort routing approach, which is not enough to support QoS. DiffServ is a standard approach for a more scalable way to achieve QoS in any IP network and could potentially be used to provide QoS in MANETs because it minimises the need for signalling. However, one of the biggest drawbacks of DiffServ is that the QoS provisioning is separate from the routing process. This thesis presents a Multipath QoS Routing protocol for 111 supporting DiffServ (MQRD), which combines the advantages of NDMR and DiffServ. The protocol can classify network traffic into different priority levels and apply priority scheduling and queuing management mechanisms to obtain QoS guarantees.

In this dissertation, analysis and design of the efficient Medium Access Control (MAC) sub-layer schemes are considered for Vehicular Ad hoc Networks (VANE~s). The contributions of this study are three-fold. First, an analytical model based on Markov chain is developed in order to investigate the performance of the MAC sub-layer of the IEEE 802.11p for vehicular communications. The results indicate that single channel MAC sub-layers may not be adequate for the future Intelligent Transportation Systems (ITS). The analytical model is validated with the results from simulation-based analysis. Performance analysis based on simulations is given on MAC metrics such as throughput, access delay, packet delivery. Second, a multi-channel MAC protocol is proposed and comprehensively analyzed in terms of channel utilizing and Quality of service (QoS) differentiation for dense VANETs. It is demonstrated that the proposed scheme, namely Asynchronous Multichannel MAC with Distributed TDMA (AMCMACD), improves the system performance in terms of throughput, packet delivery rate, collision rate on service channels, load balancing, and service differentiation for dense vehicular networks. Third, to cope with the interference from contention with neighbours within two hops in large-scale networks, a Large-scale Asynchronous Multichannel MAC (LS-AMCMAC) is proposed. The proposed scheme outperforms other benchmark multichannel MAC schemes in large-scale networks, in terms of throughput, channel utilization, dissemination of emergency messages, and the collision rates on control and service channels.

Organisational information systems development (OISD) projects have long been associated with failure. Not surprisingly, the cost of these failures is enormous. Yet, despite numerous studies, understanding of real-world projects is limited. In particular, little is known about the way in which various factors affect the success of OISD projects. Prior research has focussed on OISD projects from an in-house or client perspective, and the views of the supplier have largely been ignored. By investigating OISD project success factors from the supplier perspective, this doctoral study helps address this gap. Based on an empirical investigation drawn from data collected from Scottish IS/IT solution suppliers, this research identifies and analyses 20 success factors for supplier-based OISD projects, and a range of more detailed, inter-related sub-factors related to each of the twenty. The work confirms the importance of many factors identified in the extant literature. A number of additional factors not previously identified are also exposed. Important differences between supplier and client perspectives are revealed. The findings also develop a variety of factors that have merited scant treatment in the OISD project success factor literature. The means by which OISD project success factors propagate their influences to affect project success was also investigated. This is revealed to be a complex phenomenon comprising billions of causal chains interacting with a few million causal loops. The propagation process is performed by a sizeable network of factors, the topology of which seems to reflect the complexities of real-world OISD projects. Hence, the network is used to propose a new theory for success factors that contributes new insight into the behaviour of these projects. The research also reveals that supplier-based OISD projects are oriented more towards project success than project management success and that OISD project success criteria are far more than simply measures of success. Indeed, the overall conclusion of this thesis is that the concept of OISD project success factors is far more complicated than has been previously articulated.

This research reported in this thesis explores job search networking amongst 16-24 year olds living in Scotland, and the role of social media platforms (i.e. Facebook, Twitter, and LinkedIn) during this process. Networking is treated as an information behaviour; reflecting this, the study is underpinned by a prominent model from the domain of information science. A sequential, mixed methods approach was applied to gather data. This included the use of interviews, focus groups, and a survey questionnaire. The interviews incorporated ego-centric network methods to develop a relational perspective of job search networking. The findings show that young people accrue different types of information from network contacts which can be useful for all job search tasks. Indeed, frequent networking offline and on social media is associated with positive job search outcomes. This is especially true of engaging with family members and acquaintances, and frequent use of Facebook for job search purposes. However, demographic and other contextual factors have a substantial impact on the nature of networking behaviours, and the extent to which they can influence outcomes. Additionally, young jobseekers face a range of barriers to networking, do not always utilise their networks thoroughly, and are more likely to use social media platforms as supplementary tools for job search. A key contribution of this work is that it provides a detailed insight into the process of networking that has been neglected in previous studies. Its focus on social media also reveals a new dimension to the concept which has received little attention in the job search literature. Given its focus on young jobseekers living in Scotland, the findings have also been used to create a detailed list of recommendations for practitioners.