D. R. W. Holton

A PEPA Specification of an Industrial Production Cell

This paper describes the use of the stochastic process algebra PEPA to model and evaluate the performance of an industrial production cell. An initial specification of the production cell is is developed and transformed to allow performance measures of the cell to be found. The reasons for making these transformations are given, and performance measures for the transformed specification are presented.

Handoff mechanism in Mobile IP

Among the characteristics of the future wireless networks is the desire to support a wide range of wireless users and a diverse set of services from many different types of networks. A unifying technology for diverse wireless networking is Mobile IP, a protocol established by the Internet Engineering Task Force (IETF) that allows mobile nodes (MN) to change their point of attachment to the Internet while still being able to maintain a connection to the network Mobile IP is designed to support the mobility of a user, it is the only current means for offering seamless roaming to mobile computers in the Internet. In this paper, we give a brief survey of Mobile IP operation and functions, as well as proposed Pi-Calculus algorithm of Enhancement Mobile IP (E-Mobile IP) handoff mechanism using Link Layer Information to enhance the performance in term of packet loss and handoff latency.

Performance Evaluation of Local and Cloud Deployment of Web Clusters

Cloud computing adds more power to existing web cluster and internet technologies. A lot of research has been carried out to improve the security of such clouds. However, some users and organizations have not been able to exploit their benefits for several reasons: Firstly, some data is protected by privacy laws which prevent access or transport by third parties. Secondly some organisations fiercely protect their highly sensitive data behind their firewalls. Under these circumstances, the organisations need to use separate clusters for high security traffic and direct the rest of the traffic to a cloud cluster. This scenario leads to poor utilization in the local cluster which additionally increases the cost of the cloud. This paper introduces a model that solves the problem of cost minimisation by maximising local cluster utile and this is achieved by using a front-end load balancer for high and low security traffic. only when demand is high is low security traffic directed to the cloud. In this paper we analyze the model using queuing theory and -calculus. The performance metrics of throughput, delay, utilization and blocking probability were obtained via simulation under a range of parameters.

A class-based scheme for E-commerce web servers: Formal specification and performance evaluation

This paper is an investigation into the performance of E-commerce applications. E-commerce has become one of the most popular applications of the web as a large population of web users is now benefiting from various on-line services including product searches, product purchases and product comparison. E-commerce provides users with 24-7 shopping facilities. However, the consequence of these benefits and facilities is the excessive load on E-commerce web servers and the performance degradation of E-commerce (eCom) requests they process. This paper addresses this issue and proposes a class-based priority scheme which classifies eCom requests into high and low priority requests. In E-commerce, some requests (e.g. payment) are generally considered more important than others (e.g. search or browse). We believe that by assigning class-based priorities at multiple service levels, E-commerce web servers can perform better and can improve the performance of high priority eCom requests. In this paper, we formally specify and implement the proposed scheme and evaluate its performance using multiple servers. Experimental results demonstrate that the proposed scheme significantly improves the performance of high priority eCom requests.

Modeling and Performance Analysis of Scalable Web Servers Deployed on the Cloud

Over the last few years, cloud computing has become quite popular. It offers Web-based companies the advantage of scalability. However, this scalability adds complexity which makes analysis and predictable performance difficult. There is a growing body of research on load balancing in cloud data centres which studies the problem from the perspective of the cloud provider. Nevertheless, the load balancing of scalable web servers deployed on the cloud has been subjected to less research. This paper introduces a simple queueing model to analyse the performance metrics of web server under varying traffic loads. This assists web server managers to manage their clusters and understand the trade-off between QoS and cost. In this proposed model two thresholds are used to control the scaling process. A discrete-event simulation (DES) is presented and validated via an analytical solution.

Enhanced Mobile IP handoff using link layer information

Network layer indications are not readily available upon a link change; therefore, general dependence on the network layer may introduce unnecessary delays due to network layer signaling for a simple link layer handoff. If information could be gathered at link layer to determine the need for network layer signaling, then both the delay and signaling load could be really improved over current standards. In this paper we introduce the use of link layer information which will be the main function of the Mobile IP handoff decision to reduce packet loss and handoff latency during the handoff.

Using transputers in a robot programming and control system

Abstract In this short note we describe our experience of using transputers in a programming and control system for a teaching robot, and we outline our intentions for future work.

A Cross-Layer Decision for Mobile IP Handover

Network layer indications are not readily available upon a link change; therefore, general dependence on the network layer may introduce unnecessary delays due to network layer signaling for a simple link layer handover. If information could be gathered at link layer to determine the need for network layer signaling, then both the delay and signaling load could be really improved over the current standards of Mobile IP. This paper presents a Cross-layer decision on two layer network and link layers to improve the performance of Enhanced Mobile IP (E-Mobile IP) handover in which reducing packet loss and latency during handover process.

Performance evaluation of Mobile IPv6 fast Handover

Handover latency is the primary cause of packet loss resulting in performance degradation of the standard Mobile IPv6. Mobile IPv6 with fast Handover enables a Mobile Node (MN) to quickly detect at that IP layer it has moved to a new subnet by receiving link-related information from the link-layer; furthermore it gathers anticipative information about the new Access Point (AP) and the associated subnet prefix when the MN is still connected to the previous Corresponding Node (CN). This paper proposes an enhancement to Fast Mobile IPv6 Handover (FMIPv6), based on link layer information, we also present performance evaluations in terms of the packet loss and Handover latency using evaluation models.

Synthesis of performance management mechanisms in modern e-commerce services

Modern E-commerce services are offered in a flexible but complex setup involving multiple websites, for example, business web portals or price comparison websites, which are used in drawing the prices of a variety of online products from related websites and presenting them to millions of customers. Though this modern style of service provisioning is very attractive it significantly increases load on the web servers implementing the E-commerce services. The concern is that overloaded servers will become unresponsive and will drop requests which are beyond their capacity. This paper presents a new approach to the synthesis of performance management mechanisms, which we contend, provides more effective way for managing the performance of modern E-commerce services. The proposed approach is formally specified and is implemented as a Java-based prototype system. A number of experiments are conducted in order to test the performance management of the proposed approach.