A method of performance improvement of token ring networks is presented, based on the use of stations with two latency states. Station latency is defined as the time delay introduced in passing data through a station. Most token ring protocol standards (e.g. IEEE 802.5 or ANSI X3T9.5) require incoming data to be decoded and encoded in the station before transmission onto the ring. These encoding and decoding operations add significantly to the station latency. The bypassing of the encoding and decoding steps is proposed, which improves the mean message waiting time. A detailed evaluation and comparison of the networks is based on both analytical and simulation results. The performance of identical stations and symmetric traffic is obtained analytically. A discrete event simulation model for a token ring network is written in GPSS for general traffic. Results show a significant reduction in mean waiting time for the dual latency ring, with performance approaching or exceeding that of gated and exhaustive service, for certain ranges of network utilization. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The UbuntuNet Alliance, a consortium of National Research and Education Networks (NRENs) runs an exclusive data network for education and research in east and southern Africa. Despite a high degree of route redundancy in the Alliance's topology, a large portion of Internet traffic between the NRENs is circuitously routed through Europe. This thesis proposes a performance-based strategy for dynamic ranking of inter-NREN paths to reduce latencies. The thesis makes two contributions: firstly, mapping Africa's inter-NREN topology and quantifying the extent and impact of circuitous routing; and, secondly, a dynamic traffic engineering scheme based on Software Defined Networking (SDN), Locator/Identifier Separation Protocol (LISP) and Reinforcement Learning. To quantify the extent and impact of circuitous routing among Africa's NRENs, active topology discovery was conducted. Traceroute results showed that up to 75% of traffic from African sources to African NRENs went through inter-continental routes and experienced much higher latencies than that of traffic routed within Africa. An efficient mechanism for topology discovery was implemented by incorporating prior knowledge of overlapping paths to minimize redundancy during measurements. Evaluation of the network probing mechanism showed a 47% reduction in packets required to complete measurements. An interactive geospatial topology visualization tool was designed to evaluate how NREN stakeholders could identify routes between NRENs. Usability evaluation showed that users were able to identify routes with an accuracy level of 68%. NRENs are faced with at least three problems to optimize traffic engineering, namely: how to discover alternate end-to-end paths; how to measure and monitor performance of different paths; and how to reconfigure alternate end-to-end paths. This work designed and evaluated a traffic engineering mechanism for dynamic discovery and configuration of alternate inter-NREN paths using SDN, LISP and Reinforcement Learning. A LISP/SDN based traffic engineering mechanism was designed to enable NRENs to dynamically rank alternate gateways. Emulation-based evaluation of the mechanism showed that dynamic path ranking was able to achieve 20% lower latencies compared to the default static path selection. SDN and Reinforcement Learning were used to enable dynamic packet forwarding in a multipath environment, through hop-by-hop ranking of alternate links based on latency and available bandwidth. The solution achieved minimum latencies with significant increases in aggregate throughput compared to static single path packet forwarding. Overall, this thesis provides evidence that integration of LISP, SDN and Reinforcement Learning, as well as ranking and dynamic configuration of paths could help Africa's NRENs to minimise latencies and to achieve better throughputs.

by Chan Kwok-sum, Mak Wai-sing. / Bibliography: leaves 85-86 / Thesis (M.B.A.)--Chinese University of Hong Kong, 1986

The recent proliferation of personal wireless devices has led to the emergence of disruption-tolerant networks (DTNs), which are characterized by intermittent connectivity among some or all participating nodes and a consequent lack of contemporaneous end-to-end paths between the source and consumer of information. However, the success of DTNs as a communication paradigm is critically dependent on the following challenges being addressed: (1) How to enable popular but demanding applications, such as video-on-demand, to operate in such constrained network settings, and (2) How to incentivize individual devices to cooperate when network operation is only possible under, or greatly benefits from cooperation. In this dissertation, we present a novel set of protocols and develop real systems that effectively meet the above challenges. We make the following contributions: First, we design and implement a novel system for enabling high bandwidth content distribution in vehicular DTNs by leveraging infrastructure access points (APs). We predict which APs will soon be visited by a vehicular node and then proactively push content-of-interest to those APs. Our replication schemes optimize content delivery by exploiting Internet connectivity, local wireless connectivity, node relay connectivity and mesh connectivity among APs. We demonstrate the effectiveness of our system through trace-driven simulation and Emulab emulation using real taxi and bus traces. We further deploy our system in two vehicular networks: a fourteen AP 802.11b network and a four AP 802.11n network with smartphones and laptops as clients. Second, we propose an incentive-aware routing protocol for DTNs. In DTNs, routing takes place in a store-and-forward fashion with the help of relay nodes. If the nodes in a DTN are controlled by rational entities, such as people or organizations, the nodes can be expected to behave selfishly by attempting to maximize their utilities and conserve their resources. Since routing is inherently a cooperative activity, system operation will be critically impaired unless cooperation is incentivized. We propose the use of pair-wise tit-for-tat (TFT) as a simple, robust and practical incentive mechanism for DTNs. We then develop an incentive-aware routing protocol that allows selfish nodes to maximize their own performance while conforming to TFT constraints. / text

Thesis(M.S.)--Auburn University, 2005. / Abstract. Includes bibliographic references (p.100-103).

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science Degree in Engineering." "A thesis entitled"--at head of title. Bibliography: leaves 80-84.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 106-113). Also available in electronic version.

This thesis work is done for the department of Electronic System at The Institute of Technology at Linköping University (Linköpings Tekniska Högskolan). Study's focus is to design and implement a protocol for smart dust networks to improve the energy consumption algorithm for this kind of network. Smart dust networks are in category of distributed sensor networks and power consumption is one of the key concerns for this type of network. This work shows that by focusing on improving the algorithmic behavior of power consumption in every network element (so called as mote), we can save a considerable amount of power for the whole network. Suggested algorithm is examined using Erlang for one mote object and the whole idea has put into test for a small network using SystemC.

The advent of high-speed networks may soon increase the network bandwidth available to workstation class computers by two orders of magnitude. Combined with the dramatic increase in microprocessor speed, these technological advances make possible new kinds of applications, such as multimedia and parallel computing on networks of workstations. At the same time, the operating system, in its role as mediator and multiplexor of computing resources, is threatening to become a bottleneck. The underlying cause is that main memory performance has not kept up with the growth of CPU and I/O speed, thus opening a bandwidth gap between CPU and main memory, while closing the old gap between main memory and I/O. Current operating systems fail to properly take into account the performance characteristics of the memory subsystem. The trend towards server-based operating systems exacerbates this problem, since a modular OS structure tends to increase pressure on the memory system. This dissertation is concerned with the I/O bottleneck in operating systems, with particular focus on high-speed networking. We start by identifying the causes of this bottleneck, which are rooted in a mismatch of operating system behavior with the performance characteristics of modern computer hardware. Then, traditional approaches to supporting I/O in operating systems are re-evaluated in light of current hardware performance tradeoffs. This re-evaluation gives rise to a set of novel techniques that eliminate the I/O bottleneck.

No description available.