Jon Crowcroft

Bio: Jon Crowcroft is an academic researcher from University of Cambridge. The author has contributed to research in topics: The Internet & Multicast. The author has an hindex of 87, co-authored 672 publications receiving 38848 citations. Previous affiliations of Jon Crowcroft include Memorial University of Newfoundland & Information Technology University.

MP-ALM: Exploring Reliable Multipath Multicast Streaming with Multipath TCP

Abstract: In this paper, we present a novel idea of multipath multicast, which is imperative to bandwidth intensive applications, in the context of multimedia streaming. In addition to congestion control, multipath TCP (MPTCP) has been proposed to establish multiple paths in a network to improve network reliability. Application-layer multicast (ALM) has been proposed to leverage end systems instead of dedicated routers to multicast that is important for an easy large-scale deployment as compared to IP-based multicast. This paper presents our novel idea of multipath multicast in the form of a simple experimental framework called MP-ALM in which we combine the multiplicity feature of MPTCP with the application-layer multicast (ALM). We extensively simulate MP-ALM using ns-3 and use iPerf to generate streaming multicast-MPTCP traffic. Simulation results show that MP-ALM can be beneficial for a better user experience and reduced overall network congestion in the perspective of multicast multimedia streaming.

A QoS-negotiable middleware system for reliably multicasting messages of arbitrary size

Abstract: E-business organizations commonly trade services together with quality of service (QoS) guarantees that are often dynamically agreed upon prior to service provisioning. Violating agreed QoS levels incurs penalties and hence service providers agree to QoS requests only after assessing the resource availability. Thus the system should, in addition to providing the services: (i) monitor resource availability, (ii) assess the affordability of a requested QoS level, and (iii) adapt autonomically to QoS perturbations which might undermine any assumptions made during assessment. This paper will focus on building such a system for reliably multicasting messages of arbitrary size over a loss-prone network of arbitrary topology such as the Internet. The QoS metrics of interest will be reliability, latency and relative latency. We meet the objectives (i)-(iii) by describing a network monitoring scheme, developing two multicast protocols, and by analytically estimating the achievable latencies and reliability in terms of controllable protocol parameters. Protocol development involves extending in two distinct ways an existing QoS-adaptive protocol designed for a single packet. Analytical estimation makes use of experimentally justified approximations and their impact is evaluated through simulations. As the protocol extension approaches are complementary in nature, so are the application contexts they are found best suited to; e.g., one is suited to small messages while the other to large messages.

KylinX: Simplified Virtualization Architecture for Specialized Virtual Appliances with Strong Isolation

Abstract: Unikernel specializes a minimalistic LibOS and a target application into a standalone single-purpose virtual machine (VM) running on a hypervisor, which is referred to as (virtual) appliance. Compared to traditional VMs, Unikernel appliances have smaller memory footprint and lower overhead while guaranteeing the same level of isolation. On the downside, Unikernel strips off the process abstraction from its monolithic appliance and thus sacrifices flexibility, efficiency, and applicability. In this article, we examine whether there is a balance embracing the best of both Unikernel appliances (strong isolation) and processes (high flexibility/efficiency). We present KylinX, a dynamic library operating system for simplified and efficient cloud virtualization by providing the pVM (process-like VM) abstraction. A pVM takes the hypervisor as an OS and the Unikernel appliance as a process allowing both page-level and library-level dynamic mapping. At the page level, KylinX supports pVM fork plus a set of API for inter-pVM communication (IpC, which is compatible with conventional UNIX IPC). At the library level, KylinX supports shared libraries to be linked to a Unikernel appliance at runtime. KylinX enforces mapping restrictions against potential threats. We implement a prototype of KylinX by modifying MiniOS and Xen tools. Extensive experimental results show that KylinX achieves similar performance both in micro benchmarks (fork, IpC, library update, etc.) and in applications (Redis, web server, and DNS server) compared to conventional processes, while retaining the strong isolation benefit of VMs/Unikernels.

A fluid model approximation to quantitative information feedback in congestion control

Abstract: A new approach for deriving quantitative information for rate-based congestion schemes is presented. Using the fluid model, it is shown that the bottleneck capacity can be estimated from round trip delay when the sender is increasing its traffic rate linearly. The exact solution for a time-dependent M(t)/M(t)/1 queue verifies that the approximation is accurate when the traffic load is high. The analytical results were verified with simulation experiments, and the practical issues in applying the estimation techniques in congestion control schemes are discussed. >

BOURSE – Broadband Organisation of Unregulated Radio Systems through Economics

Abstract: This is a technical report about an idea for research in the intersection of active nets, cognitive radio and power laws of network topologies.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Community detection in graphs

Abstract: The modern science of networks has brought significant advances to our understanding of complex systems. One of the most relevant features of graphs representing real systems is community structure, or clustering, i. e. the organization of vertices in clusters, with many edges joining vertices of the same cluster and comparatively few edges joining vertices of different clusters. Such clusters, or communities, can be considered as fairly independent compartments of a graph, playing a similar role like, e. g., the tissues or the organs in the human body. Detecting communities is of great importance in sociology, biology and computer science, disciplines where systems are often represented as graphs. This problem is very hard and not yet satisfactorily solved, despite the huge effort of a large interdisciplinary community of scientists working on it over the past few years. We will attempt a thorough exposition of the topic, from the definition of the main elements of the problem, to the presentation of most methods developed, with a special focus on techniques designed by statistical physicists, from the discussion of crucial issues like the significance of clustering and how methods should be tested and compared against each other, to the description of applications to real networks.