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Title: Transmission control protocol modelling of dynamical complexity and chaos in UMTS networks
Author: Vasalos, Ioannis
Awarding Body: University of Newcastle Upon Tyne
Current Institution: University of Newcastle upon Tyne
Date of Award: 2009
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Teletraffic studies in wired networks showed that during peak traffic time chaotic dynamics appear in the network's traffic flows that can induce severe Quality of Service (QOS) degradation and destabilize network grids. The nature of these effects is targeted on the Transmission Control Protocol (TCP) as the dominant transmission protocol for data and Internet applications. These effects suggest that similar behaviour will appear in mobile networks of which the latest evolution is the Universal Mobile Telecommunications System (UMTS). So far there is still a limited understanding of UMTS traffic dynamics and performance under increased traffic loads and congestion. Therefore the objective of this Thesis is twofold. To study and analyze the nonlinear chaotic behaviour of the TCP inside the UMTS network along with the impact of this behaviour on the QoS. To present a modelling framework to portray the TCP traffic flows and capture the chaotic dynamics developed in the network traffic under increased congestion levels. Initially using the fundamentals of chaos theory chaotic dynamics in the TCP traffic flow are theoretically analysed by studying the TCP packet sending mechanism in relation to the feedback that TCP receives from the UMTS network. The theoretical analysis is validated with extensive simulation modelling of TCP traffic flows in the UMTS network under a variety of congestion level scenarios and taking into account the randomness existing in the feedback of the TCP from packet drops and packet delays inside the network. Analysis of the results is performed using the concepts of Lyapunov Exponents and exponential divergence curves as one of the strictest tests for deterministic chaos. Results showed that according to the network traffic load the TCP can exhibit from periodic to highly complex behaviour with a combination of dominant chaotic dynamics caused by the TCP and randomness induced from the network. This highly complex behaviour has a major impact on the QoS of the UMTS and results in unfairness and underutilization of the UMTS radio resources. From the theoretical model of the TCP and based on the hybrid systems modelling approach, a hybrid modelling platform is developed for modelling of the UMTS network. The model consists of continuous and discrete dynamical subsystems used to model the nonlinear dynamics of the TCP packet flow, the fading of the wireless radio channel, the Selective-Repeat Automatic Repeat Request Link Layer protocol and the packet flow in the queues of the network. The modelling implementation is extensively validated by comparison to OPNET simulations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available