| Summary: | This thesis investigates the application of the Active Networks (AN) paradigm in congestion control. ANs provide an alternative paradigm to solving network problems by allowing the network elements to perform computation. Thus, the AN is a promising paradigm to shorten the deployment time of new protocols. Congestion control is a vital element for the Internet to avoid undesirable situations such as congestion collapse. The complexity and importance of congestion control has attracted many researchers to approach it in different ways, i.e. queuing theory, control theory, and recently game theory (pricing). This thesis is concerned with the performance evaluation of AN-based congestion control protocols which have been classified according to their modes of operation, i.e. unicast, multicast single rate, and multicast multirate protocols. The research phase includes modelling and simulation experiments with the ns-2 network simulator. The first area of interest in this thesis is unicast congestion control protocols. We integrate, run and test the novel active queue management called Random Early Marking (REM) over an AN-based unicast congestion controlled network called Active Congestion Control Transmission Control Protocol. (ACC TCP). It can be concluded that the implementation of an ANs paradigm is congestion control, enhanced by the application of REM queuing policy, improves the performance of the network in terms of its low buffer occupancy and stability compared with the one using Random Early Detection (RED) queue management algorithm. Results of simulation studies comparing the performance of conventional protocols with those of AN-based protocols are presented. We investigate the TCP-friendliness behaviour of an AN-based single rate multicast congestion control called Active Error Recovery/Nominee Congestion Avoidance (AER/NCA), which uses active services to recover from loss at the point of loss and assists the congestion control. The use of AN helps the multicast application to achieve optimal data rates. We compare the results of AER/NCA TCP-friendliness to those of a single rate multicast protocols called Pragmatic General Multicast Congestion Control (PGMCC). Our simulation revealed that AER/NCA achieves the desirable property of TCP-friendliness. We also calculated AER/NCAs fairness index. For multicast multirate congestion control protocols we compare an adaptive AN-based layered multicast protocol called ALMA (Active Layered Multicast Adaptation) with a non-active network-based one called Packet-pair Receiver-driven Layered Multicast (PLM). ALMA performs layered multicast congestion control using AN approach, whereas PLM uses packet-pair techniques and fair scheduler. Experiments results shows that ALMA reacts differently from PLM in sharing the bottleneck link with CBR and TCP flows. We found that ALMA has fast convergence properties and provides flexibility to manage the network using the price function. Our experiments show that ALMA is not a TCP-friendly protocol and has a low inter-protocol fairness index.
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