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Performance Guarantees (performance + guarantee)

Distribution by Scientific Domains
Mathematics and Statistics50%

Selected Abstracts

On the hardness of range assignment problems

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2008
Bernhard Fuchs
Abstract We investigate the computational hardness of the connectivity, the strong connectivity, and the broadcast type of range assignment problems in ,2 and ,3. We present new reductions for the connectivity problem, which are easily adapted to suit the other two problems. All reductions are considerably simpler than the technically quite involved ones used in earlier works on these problems. Using our constructions, we can for the first time prove NP-hardness of these problems for all real distance-power gradients , > 0 (resp. , > 1 for broadcast) in 2D, and prove APX-hardness of all three problems in 3D for all , > 1. Our reductions yield improved lower bounds on the approximation ratios for all problems where APX-hardness was known before already. In particular, we derive the overall first APX-hardness proof for broadcast. This was an open problem posed in earlier work in this area, as was the question whether (strong) connectivity remains NP-hard for , = 1. In addition, we give the first hardness results for so-called well-spread instances. On the positive side, we prove that two natural greedy algorithms are 2-approximations for (strong) connectivity, and show that the factor 2 is tight in ,2 for , > 1. We also analyze the performance guarantee of the well-known MST-heuristic as a function of the input size. © 2008 Wiley Periodicals, Inc. NETWORKS, 2008 [source]

QoS experiences in native IPv6 networks

INTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 2 2009
Athanassios Liakopoulos
Deployment of IPv6 technology in research and commercial networks has accelerated in the last few years. Inevitably, as more advanced services take advantage of the new technology, IPv6 traffic gradually increases. Today, there is limited experience in the deployment of Quality of Service (QoS) for IPv6 traffic in backbone networks that support the Differentiated Services framework. As available software and hardware are designed to handle IPv4 packets, there is a need to accurately measure and validate performance of QoS mechanisms in an IPv6 environment. This paper discusses tests and technical challenges in the deployment of IPv6 QoS in core networks, namely the production dual stack gigabit-speed Greek Research and Education Network (GRNET) and the IPv6-only 6NET European test network, using both hardware and software platforms. In either case, we succeeded in delivering advanced transport services to IPv6 traffic and provided different performance guarantees to portions of traffic. The deployed QoS schema was common to IPv6 and IPv4; in most cases both v4 and v6 traffic exhibited comparable performance per class, while imposing no significantly different overhead on network elements. A major conclusion of our tests is that the IPv6 QoS mechanisms are efficiently supported with state-of-the-art router cards at gigabit speeds. Copyright © 2008 John Wiley & Sons, Ltd. [source]

An index policy for a stochastic scheduling model with improving/deteriorating jobs

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 7 2002
K.D. Glazebrook
We consider stochastic scheduling models which have the natural character that jobs improve while being processed, but deteriorate (and may possibly leave the system altogether) while processing is diverted elsewhere. Such restless bandit problems are shown to be indexable in the sense of Whittle. A numerical study which elucidates the strong performance of the resulting index policy is complemented by a theoretical study which demonstrates the optimality of the index policy under given conditions and which develops performance guarantees for the index heuristic more generally. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 706,721, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10036 [source]

Principles for Utilization of Seawater in the Flue-Gas Desulfurization Process

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2001
Tong Yao
The Flake-Hydro Process (SWFGD) is a flue gas desulfurization method in which sea water is used for absorption of sulfur dioxide. Shenzhen West Power Plant Unit 4 (300MW) imported this technology from Norway and installed SWFGD system. At present, the operational situation is good. All performance guarantees are secured. Shenzhen Energy Environmental Engineering Co. Ltd, also takes responsibility for monitoring and study of key techniques. [source]