Stephen Strowes

An experimental study of home gateway characteristics

Many residential and small business users connect to the Internet via home gateways, such as DSL and cable modems. The characteristics of these devices heavily influence the quality and performance of the Internet service that these users receive. Anecdotal evidence suggests that an extremely diverse set of behaviors exists in the deployed base, forcing application developers to design for the lowest common denominator. This paper experimentally analyzes some characteristics of a substantial number of different home gateways: binding timeouts, queuing delays, throughput, protocol support and others.

Self-Managed Cell: A Middleware for Managing Body-Sensor Networks

Body sensor networks consisting of low-power on- body wireless sensors attached to mobile users will be used in the future to monitor the health and well being of patients in hospitals or at home. Such systems need to adapt autonomously to changes in context, user activity, device failure, and the availability or loss of services. To this end, we propose a policy- based architecture that uses the concept of a Self-Managed Cell (SMC) to integrate services, managed resources and a policy interpreter by means of an event bus. Policies permit the declarative specification of adaptation strategy for self- configuration and self-management. We present the design and implementation of the SMC and describe its potential use in a scenario for management of heart monitoring. Preliminary performance measurements are also presented and discussed.

Policy-based Management for Body-Sensor Networks

Body sensor networks e.g., for health monitoring, consist of several low-power on-body wireless sensors, higher-level devices such as PDAs and possibly actuators such as drug delivery pumps. It is important that such networks can adapt autonomously to changing conditions such as failures, changes in context e.g., user activity, or changes in the clinical condition of patients. Potential reconfiguration actions include changing the monitoring thresholds on sensors, the analysis algorithms or the configuration of the network itself. This paper presents a policy-based approach for autonomous management of body-sensor networks using the concept of a Self- Managed Cell (SMC). Ponder2 is an implementation of this approach that permits the specification and enforcement of policies that facilitate management and adaptation of the response to changing conditions. A Tiny Policy Interpreter has also been developed in order to provide programmable decision- making capability for BSN nodes.

Towards Supporting Interactions between Self-Managed Cells

Management in pervasive systems cannot rely on human intervention or centralised decision-making functions. It must be devolved, based on local decision-making and feedback control-loops embedded in autonomous components. We have previously proposed the self-managed cell (SMC) as an architectural pattern for building ubiquitous applications, where a SMC consists of hardware and software components that form an autonomous administrative domain. SMCs may be realised at different scales, from body-area networks for health monitoring, to an entire room or larger distributed settings. However, to scale to larger systems, SMCs must collaborate with each other, and federate or compose in larger SMC structures. This paper discusses requirements for interactions between SMCs and proposes key abstractions and protocols for realising peer-to-peer and composition interactions. These enable SMCs to exchange data, react to external events and exchange policies that govern their collaboration. Dynamically customisable interfaces are used for encapsulation and interaction mediation. Although the examples used here are based on healthcare scenarios, the principles and abstractions described in the paper are more generally applicable.

An Event Service Supporting Autonomic Management of Ubiquitous Systems for e-Health

An event system suitable for very simple devices corresponding to a body area network for monitoring patients is presented. Event systems can be used both for self-management of the components as well as indicating alarms relating to patient health state. Traditional event systems emphasise scalability and complex event dissemination for internet based systems, whereas we are considering ubiquitous systems with wireless communication and mobile nodes which may join or leave the system over time intervals of minutes. Issues such as persistent delivery are also important. We describe the design, prototype implementation, and performance characteristics of an event system architecture targeted at this application domain.

Dynamic ontology mapping for interacting autonomous systems

With the emergence of mobile and ubiquitous computing environments, there is a requirement to enable collaborative applications between these environments. As many of these applications have been designed to operate in isolation, making them work together is often complicated by the semantic and ontological differences in the meta-data describing the data to be shared. Typical approaches to overcoming ontological differences require the presence of a third party administrator, an approach incompatible with autonomous systems. This paper presents an approach to automatic ontology mapping suitable for deployment in autonomous, interacting systems for a class of collaborative application. The approach facilitates the collaboration of application-level data collections by identifying areas of ontological conflict and using meta-data values associated with those collections to establish commonality. A music sharing application has been developed to facilitate the sharing of music between peers.

An experimental study of client-side spotify peering behaviour

Spotify is a popular music-streaming service which has seen widespread use across Europe. While Spotifys server-side behaviour has previously been studied, little is known about the client-side behaviour. In this paper, we describe an experimental study where we collect packet headers for Spotify traffic over multiple 24-hour time frames at a client host. Two distinct types of behaviour are observed, when tracks are being downloaded, and when the client is only serving requests from other peers. We also note wide variation in connection lifetimes, as seen in other studies of peer-to-peer systems. These findings are relevant for improving Spotify itself, and for the designers of other hybrid peer-to-peer and server-based distribution architectures.

Compact routing on the Internet AS-graph

Compact routing algorithms have been presented as candidates for scalable routing in the future Internet, achieving near-shortest path routing with considerably less forwarding state than the Border Gateway Protocol. Prior analyses have shown strong performance on power-law random graphs, but to better understand the applicability of compact routing algorithms in the context of the Internet, they must be evaluated against real-world data. To this end, we present the first systematic analysis of the behaviour of the Thorup-Zwick (TZ) and Brady-Cowen (BC) compact routing algorithms on snapshots of the Internet Autonomous System graph spanning a 14 year period. Both algorithms are shown to offer consistently strong performance on the AS graph, producing small forwarding tables with low stretch for all snapshots tested. We find that the average stretch for the TZ algorithm increases slightly as the AS graph has grown, while previous results on synthetic data suggested the opposite would be true. We also present new results to show which features of the algorithms contribute to their strong performance on these graphs.

Harnessing Internet topological stability in Thorup-Zwick compact routing

Thorup-Zwick (TZ) compact routing guarantees sublinear state growth with the size of the network by routing via landmarks and incurring some path stretch. It uses a pseudo-random landmark selection designed for static graphs, and unsuitable for Internet routing. We propose a landmark selection algorithm for the Internet AS graph that uses k-shells decomposition to choose landmarks. Using snapshots of the AS graph from 1997-2010, we demonstrate that the ASes in the kmax-shell are highly-stable over time, and form a sufficient landmark set for TZ routing in the overwhelming majority of cases (in the remainder, adding the next k-shell suffices). We evaluate path stretch and forwarding table sizes, and show that these landmark sets retain low average path stretch with tiny forwarding tables, but are better suited to the dynamic nature of the AS graph than the original TZ landmark selection algorithm.

Deterministic, reduced-visibility inter-domain forwarding

Inter-domain forwarding state is growing at a super-linear rate, rendering older routers obsolete and increasing the cost of replacement. A reduction of state will alleviate this problem. In this paper, we outline a new reduced-state inter-domain forwarding mechanism. We carefully drop portions of the advertised forwarding state using a utility measure for prefixes based on the length of the prefix and the path length to its origin. A deterministic forwarding algorithm uses the resulting partial view. The graph of connections between autonomous systems is shallow, offering many viable paths for data flows, a property we aim to use to achieve minimal detrimental effect on delay and AS path stretch.