Cameron Kiddle

Hybrid packet/fluid flow network simulation

Packet level discrete event network simulators use an event to model the movement of each packet in the network. This results in accurate models, but requires that many events are executed to simulate large, high bandwidth networks. Fluid-based network simulators abstract the model to consider only changes in rates of traffic flows. This can result in large performance advantages, though information about the individual packets is lost making this approach inappropriate for many simulation and emulation studies. We present a hybrid model in which packet flows and fluid flows coexist and interact. This enables studies to be performed with background traffic modelled using fluid flows and foreground traffic modelled at the packet level. Results presented show up to 20 times speedup using this technique. Accuracy is within 4% for latency and 15% for jitter in many cases.

SpecNet revisited: bridging flux and remote sensing communities

Spectral Network (SpecNet) began as a Working Group in 2003 with the goals of integrating remote sensing with biosphere-atmosphere carbon flux measurements and standardizing field optical sampling methods. SpecNet has evolved into an international network of collaborating sites and investigators, with a particular focus on matching optical sampling tools to the temporal and spatial scale of flux measurements and ecological sampling. Current emphasis within the SpecNet community is on greater automation of field optical sampling using simple cost-effective technologies, improving the light-use-efficiency (LUE) model of carbon dioxide flux, consideration of view and illumination angle to improve physiological retrievals, and incorporation of informatics and cyberinfrastructure solutions that address the increasing data dimensionality of cross-site and multiscale sampling. In this review, we summarize recent findings and current directions within the SpecNet community and provide recommendations for the larger remote sensing and flux communities. These recommendations include comparing the LUE model to other flux models driven by remote sensing, considering a wider array of biogenic trace gases in addition to carbon dioxide, adoption of standardized and automated field sensors and sampling protocols where possible, continued development of cyberinfrastructure tools to facilitate data comparison and integration, expanding the network itself so that a greater range of sites are covered by combined optical and flux measurements, and encouraging a broader communication between the flux and remote sensing communities.

Facebook Meets the Virtualized Enterprise

ldquoWeb 2.0rdquo and ldquocloud computingrdquo are revolutionizing the way IT infrastructure is accessed and managed. Web 2.0 technologies such as blogs, wikis and social networking platforms provide Internet users with easier mechanisms to produce Web content and to interact with each other. Cloud computing technologies are aimed at running applications as services over the Internet on a scalable infrastructure. In this paper we explore the advantages of using Web 2.0 and cloud computing technologies in an enterprise setting to provide employees with a comprehensive and transparent environment for utilizing applications. To demonstrate the effectiveness of this approach we have developed an environment that uses a social networking platform to provide access to a legacy application. The application is hosted on an internal cloud computing infrastructure that adapts dynamically to user demands. Initial feedback suggests this approach provides an improved user experience while simplifying management and increasing effective utilization of the underlying IT resources.

A Cloud-Based Interactive Application Service

Accessing, running and sharing applications and data presents researchers with many challenges. Cloud computing and social networking technologies have the potential to simplify or eliminate many of these challenges. Cloud computing technologies can provide scientists with transparent and on-demand access to applications served over the Internet in a dynamic and scalable manner. Social networking technologies provide a means for easily sharing applications and data. In this paper we present an on-line/on-demand interactive application service. The service is built on a cloud computing infrastructure that dynamically provisions virtualized application servers based on user demand. An open source social networking platform is leveraged to establish a portal front end that enables applications and results to be easily shared between researchers. Furthermore, the service works with existing/legacy applications without requiring any modifications.

Energy-cost-aware scheduling of HPC workloads

Job submission in high performance computing workloads exhibits a diurnal pattern similar to electrical prices. While high-priority jobs may need immediate access to resources, by altering the cluster scheduler to delay the execution of lower-priority jobs when power prices are high, significant cost savings can be achieved. Reduction of power demands by consumers such as data centres when energy availability is low, as signaled by high prices, can also help to simplify challenges faced in reducing the carbon footprint of the electrical grid. In this paper we discuss patterns in electrical pricing and also look at some challenges in integrating more volatile, but environmentally friendly renewable energy sources into the electrical grid. Simulation results are also presented showing that high-priority jobs can still receive rapid service while achieving 25–50% electricity cost savings for lower priority jobs.

Sequential Performance of Asynchronous Conservative PDES Algorithms

The widespread use of sequential simulation in large scale parameter studies means that large cost savings can be made by improving the performance of these simulators. Sequential discrete event simulation systems usually employ a central event list to manage future events. This is a priority queue ordered by event timestamps. Many different priority queue algorithms have been developed with the aim of improving simulator performance. Researchers developing asynchronous conservative parallel discrete event simulations have reported exceptional performance for their systems running sequentially in certain cases. This paper compares the performance of simulations using a selection of high performance central event list implementations to that achieved using techniques borrowed from the parallel simulation community. Theoretical and empirical analysis of the algorithms is presented demonstrating the range of performance that can be achieved, and the benefits of employing parallel simulation techniques in a sequential execution environment.

Addressing blocking and scalability in critical channel traversing

This paper presents two new versions of the Critical Channel Traversing (CCT) algorithm. CCT is a conservative parallel discrete event simulation algorithm that has been shown to achieve very high performance when used in a wide area computer network simulator. The first of the new algorithms called simple sender side CCT is similar to the original, but busy waiting is eliminated. Results presented show that simple sender side CCT avoids performance problems that can be caused by busy waiting.The second new algorithm called receive side CCT employs a different strategy for updating channel clocks and determining which objects should be scheduled on critical channels. Performance results show that this version provides better scaling with respect to the connectivity of the model, at the expense of some added complexity.

Improving Scalability of Network Emulation through Parallelism and Abstraction

One approach to network emulation involves simulating a virtual network with a real-time network simulator and providing an I/O interface that enables interaction between real hosts and the virtual network. This allows real protocols and applications to be tested in a controlled and repeatable environment. To reflect conditions of large networks such as the Internet it is important that the emulation environment be scalable. This paper examines improvements in scalability of the virtual network achieved through the use of parallel discrete event simulation and simulation abstraction. Using just parallel simulation techniques, real-time emulation performance of nearly 50 million packet transmissions per second is achieved on 128 processors for a network model consisting of about 20,000 nodes. Using both parallel simulation and abstraction techniques, real-time emulation performance of nearly 500 million packet transmissions per second is achieved on 128 processors for a network model consisting of about 200,000 nodes.

Green cloud VM migration: Power use analysis

To migrate virtual machines requires not only time but also energy. If pursuing a follow-the-renewables computing paradigm, migrating virtual machines between data centres on the basis of clean energy availability, understanding not only the time requirements of migration but also its energy consumption is key. Existing research has paid little attention to the energy required to perform virtual machine migrations however. In this paper we present the results of an experimental study focused on the power and energy consumption of various workloads throughout the migration process. We also discuss challenges encountered during the study restricting our ability to migrate certain types of workloads. Based on our analysis we draw conclusions about the types of workloads suitable for migration and the manner in which each can be most effectively migrated.

CyberSKA: an on-line collaborative portal for data-intensive radio astronomy

Managing the growing volume of data being output by radio telescopes is a significant challenge faced by radio astronomers today. This challenge will only be further compounded with future telescopes such as the Square Kilometre Array (SKA), which will be the worlds largest radio telescope when completed and produce data at unprecedented rates. This paper introduces the CyberSKA collaborative portal which is aimed at addressing the current and future needs of data-intensive radio astronomy. A wide variety of tools and services that have been developed and integrated with the CyberSKA portal, including a distributed data management system, a data access tool, remote visualization tools and a third party application interface are described. Current international usage of CyberSKA focusing on several different SKA Pathfinder survey projects and how they make use of the portal are also highlighted.