Νέες μέθοδοι για τον έλεγχο προσπέλασης σε δίκτυα ευρείας ζώνης
Authors: Λελίγκου Ελένη-Αικατερίνη 
Published: August 2021

The information volume and the application variety is constantly increasing imposing new demands on the telecommunication networks. The emerging technologies intend to offer new broadband services to the end users, extending the access opportunities in wider areas and broader user groups. The next step includes the development of new methods to control access that will maximize the utilization providing at the same time service differentiation, efficient switching techniques and new systems to cover the new functional requirements. The demand for Quality of Service becomes imperative nowadays with the multi-media services spreading around. The solution is pursued in the study, development and implementation of new dynamic and flexible mechanisms embedded in every networking component. Addressing this need, the dissertation investigates access mechanisms for three different systems and focuses on the service strategy and the design of the controller, which is responsible for allocating the resources satisfying a set of requirements. The first system dealt with is this of a Hybrid Fiber Co-axial network of tree-topology, where the Medium Access Controller is allocating the upstream channel slots. The MAC controller governs this distributed queuing system collecting requests from the modems and issuing transmission permits. The dissertation presents an innovative algorithm, which is aligned with the Differentiated Services architecture, to efficiently allocate the resources and provide different Quality of Service levels. The connections are grouped/aggregated in four different classes with different Quality of Service guarantees and are dynamically serviced on request basis. The implementation cost is assessed while the performance evaluation is based on results of a large set of tests that were carried out on the corresponding laboratory demonstrator system using either traffic generators boards or real applications to inject traffic in the system. A wavelength division multiplexing (WDM) ring covering metropolitan areas is the second system that is referenced. Every node attached to this ring is allowed to transmit in slots of fixed duration in multiple wavelengths at 10Gbps. A dynamic access algorithm based on the empty slot protocol is proposed to offer service differentiation. The execution of the algorithm is performed in a distributed way and is based on the information circulating in one wavelength, which carries control information. The basic scheme is this of the class reservation instead of individual node reservation. The functional requirements are analyzed while the implementation architecture is presented to certificate that the algorithm is executable in less than a slot time (1 μs) and with very little hardware resources, while backing different node’s configurations in terms of number of tunable and fixed transceivers. Finally, the access to the processing engines and to the output path of a protocol processor implemented as system on a chip is addressed. The dissertation proposes a scheme for the task and the traffic schedulers which employs flow classification and aggregation in scheduling queues and allows them to operate on the same structures -eliminating the cost- while satisfying the very different requirements imposed on them. The main result is the design of a task scheduler that supports processing throughput of 2,5Gbps and capable of implementing different service algorithms and, on the other hand, the design of a traffic scheduler which performs peak rate shaping for the transmission of both fixed size packets (e.g. ATM cells) or variable length packets (as in the case of IP networks). The implementation requirements and cost are also analyzed. The dissertation presents new methods to control access in different systems, which prove to be efficient and flexible while their implementation cost and performance is analyzed. The target has in all systems be the maximization of the utilization and the service differentiation, while their impact on the system scalability is also presented.