Dynamic buffer management policy for shared memory packet switches by employing per-queue thresholds

Gazi, Boran (2007) Dynamic buffer management policy for shared memory packet switches by employing per-queue thresholds. Doctoral thesis, Northumbria University.

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Abstract

One of the main problems concerning high-performance communications networks is the unavoidable congestion in network nodes. Network traffic is normally characterised as "bursty", which may use up network resources during peak periods. As a consequence end-user applications are subject to end-to-end delays and disruptions. Simultaneous transmission of packets on a finite bandwidth channel might result in contentions, where one or more packets are refrained from entering the transmission channel resulting in packet losses. Hence, the motivations of this thesis are two-fold: investigation and evaluation of switch architectures with electronic and optical buffers, and the development and evaluation of an improved dynamic threshold policy for shared memory switch architecture. In this work, switch architectures based on modular designs are evaluated, with simulation results showing that modular switch structures, i.e. multistage interconnection networks with optical delay line buffers, offer packet loss rate, throughput and average delay time similar to their electronic counterparts. Such optical architectures emulate prime features of shared memory switch architecture under general traffic conditions. Although the shared memory switch architecture is superior to other buffering approaches, but its performance is inadequate under imbalanced input traffic. Here its limiting features are investigated by means of numerical analysis. Different buffer management schemes, namely static thresholds, dynamic thresholds, pre-emptive, adaptive control, are investigated by using the Markov simulation model. An improved dynamic buffer management policy, decay function threshold (DFT) policy, is proposed and it is compared with the dynamic thresholds (DT), partial sharing partial partitioning (PSPP) and dynamic queue thresholds (DQT) buffer management policies by using bursty traffic source models, such as interrupted Poisson process (IPP), by means of simulations. Simulation results show that proposed policy is as good as well-known dynamic thresholds policy in the presence of best-effort traffic and offers improved packet loss performance when multicast traffic is considered. An integration framework for dynamic buffer management and bandwidth scheduling is also presented in this study. This framework employs loosely coupled buffer management and scheduling (weighted round robin, weighted fair queueing etc.) providing support for quality of service traffic. Conducted tests show that this framework matches the best-effort packet loss performance of dynamic thresholds policy.

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