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Lesaint D.,BT Research | Mehta D.,University College Cork | O'Sullivan B.,University College Cork | Quesada L.,University College Cork | Wilson N.,University College Cork
Journal of Artificial Intelligence Research | Year: 2010

Call control features (e.g., call-divert, voice-mail) are primitive options to which users can subscribe off-line to personalise their service. The configuration of a feature subscription involves choosing and sequencing features from a catalogue and is subject to constraints that prevent undesirable feature interactions at run-time. When the subscription requested by a user is inconsistent, one problem is to f find an optimal relaxation, which is a generalisation of the feedback vertex set problem on directed graphs, and thus it is an NP-hard task. We present several constraint programming formulations of the problem. We also present formulations using partial weighted maximum Boolean satisfiability and mixed integer linear programming. We study all these formulations by experimentally comparing them on a variety of randomly generated instances of the feature subscription problem. © 2010 AI Access Foundation.


Khan B.,BT Research | Goodman D.,University of Manchester | Khan S.,Solarflare Communications | Toms W.,University of Manchester | And 3 more authors.
Journal of Supercomputing | Year: 2015

To harness the compute resource of many-core system with tens to hundreds of cores, applications have to expose parallelism to the hardware. Researchers are aggressively looking for program execution models that make it easier to expose parallelism and use the available resources. One common approach is to decompose a program into parallel ‘tasks’ and allow an underlying system layer to schedule these tasks to different threads. Software-only schedulers can implement various scheduling policies and algorithms that match the characteristics of different applications and programming models. Unfortunately with large-scale multi-core systems, software schedulers suffer significant overheads as they synchronize and communicate task information over deep cache hierarchies. To reduce these overheads, hardware-only schedulers like Carbon have been proposed to enable task queuing and scheduling to be done in hardware. This paper presents a hardware scheduling approach where the structure provided to programs by task-based programming models can be incorporated into the scheduler, making it aware of a task’s data requirements. This prior knowledge of a task’s data requirements allows for better task placement by the scheduler which result in a reduction in overall cache misses and memory traffic, improving the program’s performance and power utilization. Simulations of this technique for a range of synthetic benchmarks and components of real applications have shown a reduction in the number of cache misses by up to 72 and 95 % for the L1 and L2 caches, respectively, and up to 30 % improvement in overall execution time against FIFO scheduling. This results not only in faster execution and in less data transfer with reductions of up to 50 %, allowing for less load on the interconnect, but also in lower power consumption. © 2015, Springer Science+Business Media New York.


Paverd A.J.,University of Oxford | El-Moussa F.,BT Research | Brown I.,University of Oxford
UbiComp 2014 - Adjunct Proceedings of the 2014 ACM International Joint Conference on Pervasive and Ubiquitous Computing | Year: 2014

The Personal Network (PN) is a logical network of interconnected components used by an individual. It encompasses the home network, the Personal Area Network (PAN), and the Vehicular Area Network (VAN) and includes cloud-based services. Previous security analyses, including ITU-T Recommendation X.1111, have focussed on the individual physical networks rather than the PN itself. By consolidating and structuring previous work, we propose an updated and enhanced security analysis for the PN. In our characteristic-based approach we identify the primary characteristics of the PN and its components and use these to develop an abstract PN asset model. From this, we derive the main attacker objectives and a list of attack vectors through which these could be achieved. We propose a mapping between the attack vectors and the PN component characteristics that can be used to determine the specific attacks to which a particular component is vulnerable. In this paper, we present a summary of this analysis and discuss its usage. Copyright 2014 ACM.


Kuhlewind M.,ETH Zurich | Wagner D.P.,University of Stuttgart | Espinosa J.M.R.,University of Stuttgart | Briscoe B.,BT Research
2014 IEEE Globecom Workshops, GC Wkshps 2014 | Year: 2014

Data Center TCP (DCTCP) is an Explicit Congestion Notification (ECN)-based congestion control and Active Queue Management (AQM) scheme. It has provoked widespread interest because it keeps queuing delay and delay variance very low. There is no theoretical reason why Data Center TCP (DCTCP) cannot scale to the size of the Internet, resulting in greater absolute reductions in delay than achieved in data centres. However, no way has yet been found for DCTCP traffic to coexist with conventional TCP without being starved. This paper introduces a way to deploy DCTCP incrementally on the public Internet that could solve this coexistence problem. Using the widely deployed Weighted Random Early Detection (WRED) scheme, we configure a second AQM that is applied solely to ECN-capable packets. We focus solely on long-running flows, not because they are realistic, but as the critical gating test for whether starvation can occur. For the non-ECN traffic we use TCP New Reno; again not to seek realism, but to check for safety against the prevalent reference. We report the promising result that, not only does the proposed AQM always avoid starvation, but it can also achieve equal rates. We even derived how the sharing ratio between DCTCP and conventional TCP traffic depends on the various AQM parameters. The next step beyond this gating test will be to quantify the reduction in queuing delay and variance in dynamic scenarios. This will support the standardization process needed to define new ECN semantics for DCTCP deployment that the authors have started at the IETF. © 2014 IEEE.


Menth M.,University of Tubingen | Briscoe B.,BT Research | Tsou T.,Huawei
IEEE Communications Magazine | Year: 2012

Admission control is a well-known technique to explicitly admit or block new flows in order to keep a network's traffic load at a moderate level and to guarantee QoS for admitted flows. Flow termination is a new flow control function that terminates some admitted flows when the network capacity does not suffice, such as in the case of unexpected failures. Admission control and flow termination are useful to protect QoS for inelastic flows that require a minimum bit rate. Examples are real-time applications like voice and video. Precongestion notification (PCN) provides feedback about load conditions on the path to boundary nodes. They use this information to implement lightweight admission control and flow termination without per-flow state on interior nodes of a domain. These mechanisms are significantly simpler than explicit reservation schemes. In the context of DiffServ, IP, MPLS, and Ethernet networks, we explain the concept of PCN-based admission control and flow termination, present recent standards of the IETF, and discuss benefits and limitations. © 2012 IEEE.

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