Alistair Neil Coles

The SmartFrog configuration management framework

SmartFrog is a framework for creating configuration-driven systems. It has been designed with the express purpose of making the design, deployment and management of distributed component-based systems simpler and more robust. Over the last decade it has been the focus for ongoing research into aspects of configuration management and large-scale distributed systems, providing a platform for experimentation. The paper covers the rationale for the design of the framework, details of its design, plus a description of the further research that is in progress.

A framework for coordinated multi-modal browsing with multiple clients

As users acquire or gain access to an increasingly diverse range of web access clients, web applications are adapting their user interfaces to support multiple modalities on multiple client types. User experiences can be enhanced by clients with differing capabilities combining to provide a distributed user interface to applications. Indeed, users will be frustrated if their interaction with applications is limited to one client at a time.This paper discusses the requirements for coordinating web interaction across an aggregation of clients. We present a framework for multi-device browsing that provides both coordinated navigation between web resources and coordinated interaction between variants, or representations, of those resources once instantiated in the clients. The framework protects the application from some of the complexities of client aggregation.We show how a small number of enhancements to the XForms and XML Events vocabularies can facilitate coordination between clients and provide an appropriate level of control to applications. We also describe a novel proxy which consolidates HTTP requests from aggregations of clients and reduces the burden that multi-client browsing places on the application.

Design techniques for subcarrier multiplexed broadcast optical networks

Design techniques which enable the performance of subcarrier multiplexed FM broadcast optical networks to be optimized at the planning stage are described. At the transmitter node, criteria for maximizing the subscriber carrier-to-noise ratio (CNR) are presented. At the subscriber node, it is shown that under the majority of circumstances, the optimum direct detection receiver consists of a low-noise III-V avalanche photodiode and high-impedance front-end preamplifier. Sensitivities approaching -40 dB (1 mW) for 16.5 dB CNR in 36 MHz subscriber bandwidth are predicted for a 60-channel system. Preliminary experimental tests on an optical-feedback subcarrier receiver showed -34 dB (1 mW) sensitivity at 1.55 mu m from 16.5 dB CNR in a 36 MHz bandwidth centered on 1.2 GHz with a 12% modulation index single-channel FM test signal. >

Rapid Node Reallocation Between Virtual Clusters for Data Intensive Utility Computing

Utility computing achieves efficiencies by dynamically reallocating shared resources between services operating on virtual clusters. These efficiencies can be hard to realize for data intensive applications; newly allocated nodes must be populated with a large amount of data which impedes rapid node reallocation. We describe a data management architecture that uses disk caches on each node to reduce data copying and speed up node reallocation for data intensive applications. Cache consistency management is simplified by extensive use of copy-on-write techniques. A data-driven scheme is then used to select nodes for reallocation between virtual clusters based on the amount of relevant cached data. These nodes are identified using a novel technique of statistically sampling the contents of caches. We demonstrate the benefits of this architecture using our implementation of an efficient block level caching and copy-on-write target for the Linux device-mapper framework

High-speed Storage Nodes for the Cloud

In this paper, we describe an architecture for high-speed storage nodes intended for supporting cloud-based storage I/O intensive applications such as file servers, backup servers and databases. The nodes can host multiple virtual machines each having direct access to a storage array via Single Route I/O Virtualization (SR-IOV). This is done in a way which does not compromise security. We demonstrate that SR-IOV imposes negligible overhead for storage I/O and provides the hosted virtual machines with four times the storage I/O bandwidth than is available from the same hardware when I/O is redirected through the hyper visor. We describe how the storage nodes are incorporated into a heterogeneous Infrastructure as a Service (IaaS) consisting of mixed storage and compute nodes.

100 Mb/s data transmission on UTP and STP cabling for demand priority networks

There have been considerable advances towards higher speed (100 Mb/s) workgroup LANs which support the existing UTP and STP structured cabling utilized by 10 BASE-T and token ring LANs. The paper describes the transmission techniques used by an IEEE 802.12 demand priority network with UTP and STP structured cabling. The UTP transmission scheme supports categories 3-5 UTP (i.e. voice-grade and data-grade) using a 5B6B block coded binary signalling scheme on four pairs. This binary signalling scheme is shown to provide better immunity against crosstalk and external (impulse) noise than multilevel signalling schemes. The STP scheme combines the strengths of the 5B6B block code with signalling technology similar to existing SDDI links.

Cells: A Self-Hosting Virtual Infrastructure Service

We describe the design and implementation of Cells, a novel multi-tenanted virtual infrastructure service. Cells has the unique property of being self-hosting: it operates its own management system within one of the tenant virtual infrastructures that it manages and therefore benefits from the same security, flexibility and scalability as other tenant services. Cells is also differentiated by its declarative interface for infrastructure configuration, and its fine-grained control of network and storage connections within and between tenant infrastructures.

New pseudorandom sequence measurement technique for subcarrier multiplexed distribution networks

The nonlinear characteristics of subcarrier network electronic, optoelectronic, and optical components set an upper limit to the available carrier to noise ratio (CNR). Conventionally, the harmonic and intermodulation distortion of system components such as semiconductor lasers has been assessed with multitone tests (e.g., Ref. 1). While these measurements give an accurate account of laser nonlinearity, they do not reflect the spectral characteristics of active communication channels. The statistical properties of the subcarrier channel signal ensemble must also be considered since peak signal clipping can introduce further CNR degradation.2 These issues are common to frequency-division-multiplex radio systems where it has been found that Gaussian statistics only apply with more than sixty speech signals (e.g., Ref. 3). Consequently, a new test procedure for the emerging subcarrier optical network systems is required.