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Author

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.


Papers
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Proceedings ArticleDOI
09 Dec 2013
TL;DR: A detailed picture of the mechanisms selected to implement online presence, along with their effect on handset energy consumption and network signaling traffic is revealed, and it is found that a two-way push notification system, with messages being sent at a low (regular) frequency and low volume by a network-aware sender, can alleviate many of the costs.
Abstract: Mobile phones in the 3G/4G era enable us to stay connected not only to the voice network, but also to online services like social networks. In this paper, we study the energy and network costs of mobile applications that provide continuous online presence (e.g. WhatsApp, Facebook, Skype). By combining measurements taken on the mobile and the cellular access network, we reveal a detailed picture of the mechanisms selected to implement online presence, along with their effect on handset energy consumption and network signaling traffic. We are surprised to find that simply having idle online presence apps on a mobile (that maintain connectivity in the background, with no user interaction) can drain the handset battery nine times more quickly. This high cost is partly due to online presence apps that are excessively ``chatty'', in particular when their design philosophy stems from a similar desktop version. However, we also find that the cost of background app traffic is disproportionately large because of cross-layer interactions in which the traffic unintentionally triggers the promotion of cellular network states. Our experiments show that both of these effects can be overcome with careful implementation. We posit that a two-way push notification system, with messages being sent at a low (regular) frequency and low volume by a network-aware sender, can alleviate many of the costs.

47 citations

Proceedings Article
01 Aug 2004
TL;DR: Preliminary results are presented showing that Vigilante can effectively contain fast spreading worms that exploit unknown vulnerabilities, and is proposed as a new host centric approach for automatic worm containment.
Abstract: Worm containment must be automatic because worms can spread too fast for humans to respond. Recent work has proposed a network centric approach to automate worm containment: network traffic is analyzed to derive a packet classifier that blocks (or rate-limits) worm propagation. This approach has fundamental limitations because the analysis has no information about the application vulnerabilities exploited by worms. This paper proposes Vigilante, a new host centric approach for automatic worm containment that addresses these limitations. Vigilante relies on collaborative worm detection at end hosts in the Internet but does not require hosts to trust each other. Hosts detect worms by analysing attempts to infect applications and broadcast self-certifying alerts (SCAs) when they detect a worm. SCAs are automatically generated machine-verifiable proofs of vulnerability; they can be independently and inexpensively verified by any host. Hosts can use SCAs to generate filters or patches that prevent infection. We present preliminary results showing that Vigilante can effectively contain fast spreading worms that exploit unknown vulnerabilities.

47 citations

Journal ArticleDOI
TL;DR: Vigilante is proposed, a new end-to-end architecture to contain worms automatically that addresses limitations of network-level techniques to automate worm containment and does not require any changes to hardware, compilers, operating systems, or the source code of vulnerable programs.
Abstract: Worm containment must be automatic because worms can spread too fast for humans to respond. Recent work proposed network-level techniques to automate worm containment; these techniques have limitations because there is no information about the vulnerabilities exploited by worms at the network level. We propose Vigilante, a new end-to-end architecture to contain worms automatically that addresses these limitations.In Vigilante, hosts detect worms by instrumenting vulnerable programs to analyze infection attempts. We introduce dynamic data-flow analysis: a broad-coverage host-based algorithm that can detect unknown worms by tracking the flow of data from network messages and disallowing unsafe uses of this data. We also show how to integrate other host-based detection mechanisms into the Vigilante architecture. Upon detection, hosts generate self-certifying alerts (SCAs), a new type of security alert that can be inexpensively verified by any vulnerable host. Using SCAs, hosts can cooperate to contain an outbreak, without having to trust each other. Vigilante broadcasts SCAs over an overlay network that propagates alerts rapidly and resiliently. Hosts receiving an SCA protect themselves by generating filters with vulnerability condition slicing: an algorithm that performs dynamic analysis of the vulnerable program to identify control-flow conditions that lead to successful attacks. These filters block the worm attack and all its polymorphic mutations that follow the execution path identified by the SCA.Our results show that Vigilante can contain fast-spreading worms that exploit unknown vulnerabilities, and that Vigilante's filters introduce a negligible performance overhead. Vigilante does not require any changes to hardware, compilers, operating systems, or the source code of vulnerable programs; therefore, it can be used to protect current software binaries.

46 citations

Journal ArticleDOI
01 Jun 2009
TL;DR: It is argued that people, architecture and technology together provide the infrastructure for these applications and an understanding of this infrastructure is important for effective design and development.
Abstract: The increasing popularity of mobile computing devices has allowed for new research and application areas. Specifically, urban areas exhibit an elevated concentration of such devices enabling potential ad-hoc co-operation and sharing of resources among citizens. Here, we argue that people, architecture and technology together provide the infrastructure for these applications and an understanding of this infrastructure is important for effective design and development. We focus on describing the metrics for describing this infrastructure and elaborate on a set of observation, analysis and simulation methods for capturing, deriving and utilising those metrics.

45 citations

Proceedings ArticleDOI
10 Dec 2010
TL;DR: This paper presents a novel Inter-MANET Routing protocol called InterMR that can handle the heterogeneity and dynamics of MANETs, and shows that the performance of InterMR can be improved by up to 112% by adaptive gateway assignment functionalities.
Abstract: The advancements of diverse radio technologies and emerging applications have spawned increasing heterogeneity in mobile ad hoc networks (MANETs). But the collaborative nature of communications and operations often requires that these heterogeneous MANETs to be interoperable. Nonetheless, the existing interconnection protocols designed for the Internet (namely inter-domain routing protocol such as BGP) are not adequate for handling the unique challenges in MANETs. In this paper, we present a novel Inter-MANET Routing protocol called InterMR that can handle the heterogeneity and dynamics of MANETs. Our first contribution is an Inter-MANET address scheme based on a variety of node attributes (e.g., symbolic name, property, etc.); this allows dynamic merging/split of network topologies without a separate Name Server. Our second contribution is to provide a seamless routing mechanism across heterogeneous MANETs without modifying the internal routing mechanisms in each MANET. The proposed scheme can transparently adapt to topological changes due to node mobility in MANETs by dynamically assigning the gateway functionalities. We show, by packet-level simulation, that the performance of InterMR can be improved by up to 112% by adaptive gateway assignment functionalities. We also show that InterMR is scalable with only modest overhead by analysis.

44 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
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 …

33,785 citations

Journal ArticleDOI
TL;DR: In this paper, Imagined communities: Reflections on the origin and spread of nationalism are discussed. And the history of European ideas: Vol. 21, No. 5, pp. 721-722.

13,842 citations

Journal ArticleDOI
TL;DR: A thorough exposition of community structure, or clustering, is attempted, 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.
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.

9,057 citations

Journal ArticleDOI
TL;DR: A thorough exposition of the main elements of the clustering problem can be found in this paper, 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.

8,432 citations