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.

Future Internet (Dagstuhl Seminar 13131)

Abstract: This report documents the program and the outcomes of Dagstuhl Seminar 13131 "Future Internet". At the seminar, about 40 invited researchers from academia and industry discussed the promises, approaches, and open challenges of the Future Internet. This report gives a general overview of the presentations and outcomes of discussions of the seminar.

Performance comparison of CRAM, SEAM and SPAM multipoint VC schemes for ATM networks

Abstract: Multicast service is an important part of any modern routing architecture. Motivations for many-to-many multicast include general unpredictability of membership in many real applications; simplicity of the rendezvous for the application programmer; and low cost to end systems and switches in terms of state to maintain for the delivery tree. Shared trees have an even greater advantage over source based trees in the latter respect. Shared trees (as in the CBT model for Internet) are supported in the form of a single logical VC per multicast group (i.e., multipoint-to-multipoint VC or mp-mp VC) in the ATM networks. CRAM, SEAM and SPAM have been previously proposed for supporting mp-mp VC. The work in this paper does a performance comparison of these three schemes, with respect to buffer requirements, end-to-end delay, packet jitter and traffic overhead. Our evaluation is carried out through extensive simulations with different topologies and sender traffic types.

Tearing down the Protocol Wall with Software Defined Networking

Abstract: The letter of the law of Software Defined Networking (SDN) is the OpenFlow specification, combined with appropriate controllers. The spirit of the law of SDN affords much more potential for innovation. We take the position that the future of communications is at stake unless the Protocol Wall is overcome. By "Protocol Wall" we mean the artificial barrier which, until recently, has been placed between the inflexible, protocol-bound communications space, and the application space in which far fewer constraints are placed on the programmer and in which far more innovative results can be achieved. Overcoming the Protocol Wall allows fully programmable, software-defined behaviour in both the data plane and the control plane, and opens the way for much-needed innovations in networking. In the stereotypical case, of which sockets are an example, the application functionality and the physical layer are separated between kernel and user respectively, with the kernel below the transport service layer, and the application above it. Archetypically, the router and host are separated between Internet Protocol (IP) and Transmission Control Protocol (TCP) respectively, where IP is responsible for hop-by-hop forwarding and TCP for end-to-end services. The Protocol Wall between application functionality and the physical layer constitutes a hegemony over innovation which is not being challenged sufficiently by current SDN approaches. We assert that the realisation of unconstrained Software Defined Networking is closer at hand than anyone has yet acknowledged, and that networking can be evolved more quickly if we are guided by the spirit of the law of SDN. User mode network software, running on today's commodity and specialised communications hardware, can safely support satisfactory performance, while opening up potential for the same very high rate of innovation in networking as has been seen in appliances - for example, in smart mobile devices - in recent years.

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.