Ali, Ashraf

English

Mission Critical Systems (MCSs) are needed mainly as All-Time-Available backbone system for emergencies, crises, and disaster scenarios. They are used in Public Protection and Disaster Relief (PPDR) operations, Utility Networks, and Intelligent Transportation Systems. Due to the critical nature of MCSs, they need to adhere to strict requirements to ensure the accomplishment of tasks and duties that are usually strongly associated with human lives and national security. Delay, Interoperability, Availability, Reliability, Security, and Resilience are some of the requirements that need to be met by an MCS to ensure optimum functionality as required by its users. There are two main deployment options for an MCS; the first is a dedicated system, such as TErristrial Trunked Radio (TETRA), that is designed to meet all the MCS requirements and which operates only for mission critical operations and tasks, while the second is a commercial general purpose mobile communication system that can be used for both conventional mobile communication as well as an MCS. The first option can only support low data rates to support limited applications. Whereas the second option can provide users with broadband services using a more generic communication system that can be used as an MCS as well as conventional mobile communications system, but it lacks the scalability and reliability support provided by dedicated MCSs.This research, articulated in this thesis, de-risks the compliance of a new mission critical system proposed by standardisation bodies and governmental authorities, merging the strengths of both dedicated and generic mobile communication systems, to meet the MCS requirements. Delay of Session Initiation Protocol (SIP) signalling between different entities in the core network, such as in IP Multimedia Subsystem (IMS), is considered one of the major factors that contributes to the Scalability, Reliability, and end-to-end delay challenges of generic next generation MCS. This thesis, presents a literature study of recent findings and enhancements in signalling domain, in addition to an appraisal of the multimedia communications signalling performance metrics and evaluation techniques along with a bottleneck analysis of the core network entities. A systematic methodology to run a set of experiments and evaluation techniques was developed by referring to recent methodological techniques found in the literature and a new framework was designed and evaluated to overcome the challenges of dedicated systems.The evaluation, using simulations and experimental testbed, showed the effect of SIP signalling delay over the overall system performance in terms of scalability and robustness. Simulation results showed the delay effects introduced by the access technology over the entire system performance. Moreover, the testbed results, using different systematic scenarios, showed the core network part effect over the entire system performance especially the scalability, responsiveness, and reliability aspects. Both, the simulations and testbed experiments, show that there is a need to improve the performance of the current real-time processing techniques at the user end interface (access technology domain) and the core end subsystems (IMS and related interfaces) to compensate for the performance impairments. The framework proposed, was able to process the traffic in real time and send feedback information utilising the information found in the header of different network layers to decide a load balancing mechanism able to minimise the end-to-end delay and scalability shortcoming during heavy load scenarios

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Mission Critical Communication Systems: Performance Evaluation, Enhancement, and Modelling

https://pure.southwales.ac.uk/ws/files/3598439/PhD_Thesis_Ashraf_Ali_Final_postViva.pdf

Mission Critical Communication Systems: Performance Evaluation, Enhancement, and Modelling

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