Analytical Modelling of Scheduling Schemes under Self-similar Network Traffic. Traffic Modelling and Performance Analysis of Centralized and Distributed Scheduling Schemes.

High-speed transmission over contemporary communication networks has drawn many research efforts. Traffic scheduling schemes which play a critical role in managing network transmission have been pervasively studied and widely implemented in various practical communication networks. In a sophisticated communication system, a variety of applications co-exist and require differentiated Quality-of-Service (QoS). Innovative scheduling schemes and hybrid scheduling disciplines which integrate multiple traditional scheduling mechanisms have emerged for QoS differentiation. This study aims to develop novel analytical models for commonly interested scheduling schemes in communication systems under more realistic network traffic and use the models to investigate the issues of design and development of traffic scheduling schemes. In the open literature, it is commonly recognized that network traffic exhibits self-similar nature, which has serious impact on the performance of communication networks and protocols. To have a deep study of self-similar traffic, the real-world traffic datasets are measured and evaluated in this study. The results reveal that selfsimilar traffic is a ubiquitous phenomenon in high-speed communication networks and highlight the importance of the developed analytical models under self-similar traffic. The original analytical models are then developed for the centralized scheduling schemes including the Deficit Round Robin, the hybrid PQGPS which integrates the traditional Priority Queueing (PQ) and Generalized Processor Sharing (GPS) schemes, and the Automatic Repeat reQuest (ARQ) forward error control discipline in the presence of self-similar traffic. Most recently, research on the innovative Cognitive Radio (CR) techniques in wireless networks is popular. However, most of the existing analytical models still employ the traditional Poisson traffic to examine the performance of CR involved systems. In addition, few studies have been reported for estimating the residual service left by primary users. Instead, extensive existing studies use an ON/OFF source to model the residual service regardless of the primary traffic. In this thesis, a PQ theory is adopted to investigate and model the possible service left by selfsimilar primary traffic and derive the queue length distribution of individual secondary users under the distributed spectrum random access protocol

Delay-aware Link Scheduling and Routing in Wireless Mesh Networks

Resource allocation is a critical task in computer networks because of their capital-intensive nature. In this thesis we apply operations research tools and technologies to model, solve and analyze resource allocation problems in computer networks with real-time traffic. We first study Wireless Mesh Networks, addressing the problem of link scheduling with end-to-end delay constraints. Exploiting results obtained with the Network Calculus framework, we formulate the problem as an integer non-linear optimization problem. We show that the feasibility of a link schedule does depend on the aggregation framework. We also address the problem of jointly solving the routing and link scheduling problem optimally, taking into account end-to-end delay guarantees. We provide guidelines and heuristics. As a second contribution, we propose a time division approach in CSMA MAC protocols in the context of 802.11 WLANs. By grouping wireless clients and scheduling time slots to these groups, not only the delay of packet transmission can be decreased, but also the goodput of multiple WLANs can be largely increased. Finally, we address a resource allocation problem in wired networks for guaranteed-delay traffic engineering. We formulate and solve the problem under different latency models. Global optimization let feasible schedules to be computed with instances where local resource allocation schemes would fail. We show that this is the case even with a case-study network, and at surprisingly low average loads

Performance Analysis of Modified Deficit Round Robin Schedulers

Deficit Round Robin (DRR) is a scheduling algorithm which provides fair queuing at O(1) complexity. However, due to its round robin structure, its latency properties are not adequate for latency-critical applications, such as voice. For this reason, router manufacturers implement variants of the DRR algorithm which guarantee lower latencies to one (or a subset of) queue(s). In this paper we evaluate the performance of two such variants, both of which are known as Modified Deficit Round Robin, currently implemented in commercial routers. The comparison is carried out analytically, by deriving the latency and bandwidth guarantees of both algorithms, and by simulation