21934561
Location and Configuration Management in Mobile-Switch ATM Networks
The features of two important application scenarios, supporting mobile switches with fixed end users and mobile switches with mobile users, are dramatically different from those of the traditional wired network structure. To exploit mobile switches, the location and configuration management of mobile switches is essential to handle the mobility and topology change of the wireless/mobile ATM network. In this paper we address the location management and configuration problems of mobile switches in an ATM network. We investigate several aspects of the location management problem including architecture to support switch mobility, mobile switch tracking, and mobile switch locating. We propose an approach that is based on the Private Network-Network Interface (PNNI) protocol. We extend the PNNI protocol to enable it to handle mobile switches. Moreover, we develop analytical models to determine the tracking and locating costs for mobile switches under the proposed scheme. The models illustrate the relation between total cost (tracking cost + locating cost) and peer group size. The models can be used to derive the optimal configuration for an ATM network with mobile switches.
30645069
Backtrack Routing and Priority-Based Wavelength Assignment in WDM Networks
In this paper, we consider two key problems in the WDM networks: the wavelengh assignment and routing problems. The objective of the problems is to minimize the request blocking rate. We propose two priority-based methods for the wavelength assignment problem: static and dynamic strategies. Based on the priority of an incoming request, the proposed methods allocate a wavelength among the available wavelengths for the given priority. Analytic models and simulations are presented for the proposed wavelength assignment methods so as to analyse the link blocking rate. The simulation results show that the link blocking rate by the dynamic strategy is less than that by the assignment strategy. We also develop a routing algorithm that works together with the proposed wavelength assignment methods to reduce the overall blocking rates. The proposed routing method maintains a routing tree for a given connection request. Based on the routing tree, the algorithm finds a route with one available wavelength for each link along the route. We compare the proposed routing method with the fixed routing and fixed alternate routing algorithms. The experiments show that the proposed routing algorithm performs better than the fixed routing and the alternate routing methods.
14292166
A self-adjusting quality of service control scheme
We propose and analyze a self-adjusting Quality of Service (QoS) control scheme with the goal of optimizing the system reward as a result of servicing different priority clients with varying workload, QoS and reward/penalty requirements. Our scheme is based on resource partitioning and designated "degrade QoS areas" such that system resources are partitioned into priority areas each of which is reserved specifically to serve only clients in a corresponding class with no QoS degradation, plus one "degraded QoS area" into which all clients can be admitted with QoS adjustment being applied only to the lowest priority clients. We show that the best partition is dictated by the workload and the reward/penalty characteristics of clients in difference priority classes. The analysis results can be used by a QoS manager to optimize the system total rewawrd dynamically in response to changing workloads at run time. We demonstrate the validity of our scheme by means of simulation and comparing the proposed QoS self-adjusting scheme with those that do not use resource partitioning or designated degraded QoS area.
117206
On Integrated Location and Service Management for Minimizing Network Cost in Personal Communication Systems
We investigate the notion of per-user integrated location and service management in personal communication service (PCS) networks by which a Per-user service proxy is created to serve as a gateway between the mobile user and all client-server applications engaged by the mobile user. The service proxy is always colocated with the mobile user's location database such that whenever the MU's location database moves during a location handoff, a service handoff also ensues to colocate the service proxy with the location database. This allows the proxy to know the location of the mobile user all the time to reduce the network communication cost for service delivery. We investigate four integrated location and service management schemes. Our results show that the centralized scheme performs the best when the mobile user's SMR (service to mobility ratio) is low and CMR (call to mobility ratio) is high, while the fully distributed scheme performs the best when both SMR and CMR are high. In all other conditions, the dynamic anchor scheme is the best except when the service context transfer cost is high, under which the static anchor scheme performs the best. Through analytical and simulation results, we demonstrate that different users with vastly different mobility and service patterns should adopt different integrated location and service management methods to optimize system performance. Further, the best integrated scheme always performs better than the best decoupled scheme that considers location and service managements separately and management schemes that do not use any service proxy
1362947
Optimal Replication of Series-Parallel Graphs for Computation-Intensive Applications
Abstract We consider the replication problem of series-parallel (SP) task graphs where each task may run on more than one processor. The objective of the problem is to minimize the total cost of task execution and interprocessor communication. We call it the minimum cost replication problem for SP graphs (MCRP-SP). In this paper, we adopt a new communication model where the purpose of replication is to reduce the total cost. The class of applications we consider is computation-intensive applications in which the execution cost of a task is greater than its communication cost. The complexity of MCRP-SP for such applications is proved to be NP-complete. We present a branch-and-bound method to find an optimal solution as well as an approximation approach for a suboptimal solution. The numerical results show that such replication may lead to a lower cost than the optimal assignment problem (in which each task is assigned to only one processor) does. The proposed optimal solution has complexity O ( n 2 2 n M ), while the approximation solution has O ( n 4 M 2 ), where n is the number of processors in the system and M is the number of tasks in the graph.
29681392
Schedulability-oriented replication of periodic tasks in distributed real-time systems
We consider the schedulability-oriented replication problem of a set of periodic real-time tasks where each task can be decomposed into several modules and intermodule communications. The objective is to find an allocation in which there exists a feasible schedule for the given task set. In this paper, we adopt a communication model where the replication of modules is not for the sake of fault tolerance but for increasing the degree of schedulability. To solve the problem, we develop a replication technique and embed the technique in a simulated annealing algorithm. Experimental results show that such replication may lead to a higher degree of schedulability and obtain a feasible solution.
15145046
A novel approach to diagnose diabetes based on the fractal characteristics of retinal images
A novel diagnostic scheme to develop quantitative indexes of diabetes is introduced in this paper. The fractal dimension of the vascular distribution is estimated because we discovered that the fractal dimension of a severe diabetic patient's retinal vascular distribution appears greater than that of a normal human's. The issue of how to yield an accurate fractal dimension is to use high-quality images. To achieve a better image-processing result, an appropriate image-processing algorithm is adopted in this paper. Another important fractal feature introduced in this paper is the measure of lacunarity, which describes the characteristics of fractals that have the same fractal dimension but different appearances. For those vascular distributions in the same fractal dimension, further classification can be made using the degree of lacunarity. In addition to the image-processing technique, the resolution of original image is also discussed here. In this paper, the influence of the image resolution upon the fractal dimension is explored. We found that a low-resolution image cannot yield an accurate fractal dimension. Therefore, an approach for examining the lower bound of image resolution is also proposed in this paper. As for the classification of diagnosis results, four different approaches are compared to achieve higher accuracy. In this study, the fractal dimension and the measure of lacunarity have shown their significance in the classification of diabetes and are adequate for use as quantitative indexes.
1223930
Approximate Strategic Reasoning through Hierarchical Reduction of Large Symmetric Games
To deal with exponential growth in the size of a game with the number of agents, we propose an approximation based on a hierarchy of reduced games. The reduced game achieves savings by restricting the number of agents playing any strategy to fixed multiples. We validate the idea through experiments on randomly generated local-effect games. An extended application to strategic reasoning about a complex trading scenario motivates the approach, and demonstrates methods for game-theoretic reasoning over incompletely-specified games at multiple levels of granularity. Motivation Consider the task of selecting among a large set of strategies to play in an 8-player game. Through careful judgment you manage to narrow down the candidates to a reasonable number of strategies (say 35). Because the performance of a strategy for one agent depends on the strategies of the other seven, you wish to undertake a game-theoretic analysis of the situation. Determining the payoff for a particular strategy profile is expensive, however, as your observations of prior game instances are quite limited, and the only operational description of the game is in the form of a simulator that takes a non-negligible time (say 10 minutes) to produce one outcome. Moreover, since the environment is stochastic, numerous samples (say 12) are required to produce a reliable estimate for even one profile. At two hours per profile, ex
16505104
Approximate minimum weight Steiner triangulation in three dimensions
ApproximateMinimumWeightSteinerTriangulationinThreeDimensionsSiu-WingChengyTamal K. DeyAbstractDicultyofminimumweighttriangulationap oinsetinR2is well known.In this pap er we study the minimumweight triangulation problem for p olyhedra and general ob-stacle set in three dimensions.The weight of a triangulationin three dimensionsis assumed to b e the total surface areaof alltrianglesinvolved.It isshownthat ap olyhedronPof sizencan b e triangulated withO(2log) tetrahedra intimeO(n2log3) approximating the minimum weight trian-gulation ofPwithin a constant factor. No such prior resultisknown.Thesameb oundsalsoholdfor a3Dp ointsettriangulationallowingSteiner p oints.We consider anothersetting called general obstacle set, where the convex hull ofa set ofntrianglesis triangulatedconforming to the inputtriangles.In thiscase we show thatour metho dpro ducesa triangulati onof sizeO(n3log) in time) ap-proximating the weight of the minimum wt triangulationwithin a constant factor. This is a considerable improvementover theO(n6) b ound known for this case [3]. It is shown in[3] that minimumweighttriangulationisgo o dfor averagecase ray sho oting in three dimensions.This further substan-tiates the signi cance of our result.1Intro ductionThe minimum weight triangulation (MWT) problem ismostwell-knownintheplane,whereatriangulationwiththeminimumtotaledgelengthissoughtfora2Dp ointset.Theproblemisnotknowntob eNP-hard but no p olynomial-time algorithm is known.Re-centlyanapproximation algorithm withconstantfac-tor p erformance guarantee has b een designed for MWTby Levcop oulos and Krznaric[10].In another versionof theproblem Steinerp ointsareallowed andamini-mum weight Steinertriangulation (MWST)among allp ossibleSteinertriangulationsisdesired.Inparticu-lar, MWT is also a Steiner triangulation but with zeroSteiner p oints.Eppstein [8] showed how to approximatethe MWST of a 2Dp oint set within a constant factor.Instead of a 2Dp oint set, general inputs such as planarstraight line graphs (PSLG) have also b eenconsideredDepartment of Computer Science, HKUST, Hong Kong.e-mail: scheng@cs.ust.hkyDepartmentofCSE,I ITKharagpur,Kharagpur721302,India. e-mail: dey@cse.iitkgp.ernet.infor their applications in ray sho oting [3, 7]. A triangula-tion of a PSLG is the decomp osition of the convex hullof its verticeswhere the input line segments app ear asedges.When Steiner p oints are allowed these segmentsmay app ear as union of edges.Aronov and Fortune [3]observe that the technique of [8] applies to this case topro duce a p olynomial size triangulation approximatingMWSTwithinaconstantfactor.Inthesp ecialcasewhen the input PSLG is a p olygon p ossibly with holes,Cheng and Lee [7] presented an algorithm with b oth sizeand running timeO(nlog), whereis the numb er ofedges.Thetriangulationofap ointsetin3Disthedecomp osition of its convex hull into disjoint tetrahedra.The weight of the triangulation is the sum of the area ofthe triangles in it.Instead of p oint sets, the input mayconsist of a set of triangles with disjoint relative interior,acounterpartofPSLGin3D.Inthissettingcalledgeneral obstacle set, a minimum weight triangulation ofthe convex hull is sought where the input triangles haeto b e conformed.A sp ecial case arises when the inputtrianglesformtheb oundaryofap olyhedronwhoseinterioristob etriangulatedwithminimumweight.Noticethattheformulationofminimumweighttriangulation problem in these cases must allow Steinerp oints since there are arrangements of triangles in threespace such as the b oundary of Schonardt p olyhedron forwhich no triangulation is p ossible without Steiner p oints[12].WeconsiderMWSTproblemforthreedi erentcategories of inputs:p olyhedra, p oint sets, and generalobstaclesets.Of course,thisleaves op entheproblemof MWT of a 3Dp oint set since a p oint set can alwaysb e triangulated without Steiner p oints.ResultonMWSTprobleminthreedimensionsisscarce.Eppstein, in his pap er [8], acknowledges the dif- culty of the problem and observes the obstacles in gen-eralizing a metho d working in two dimension. When thelengths of the edges are taken as weights, he shows thatthemetho dcanb emo di edtopro duceanO(logn)-factorapproximation toMWSTofap ointset.How-ever,withareasoftrianglestakenastheweights,metho d could not b e generalized.Aronov and Fortune[3], building up on the technique of Eppstein showed hotopro duceanO(n6)sizetriangulation approximatingthe MWST of a general obstacle set.They argued that1
206577228
Fast Trellis-Coded Color Quantization of Images
We examine color quantization of images using trellis-coded quantization (TCQ) in both the RGB domain and YUV domain. Together with a simple dithering scheme, an eight-bit trellis-coded color quantizer reproduces images that are visually indistinguishable from the 24-bit originals. It can be viewed as a predictive trellis-coded color quantization scheme. We also study trellis-coded vector quantization (TCVQ) for color quantization. Our proposed TCQ-based color quantization schemes are universal in the sense that no training or look-up table is needed. The complexity of TCQ is linear with respect to image size, making trellis-coded color quantization suitable for color printing, real-time interactive graphics and window-based display environment.
6799009
On packetization of embedded multimedia bitstreams
We study the problem of packetizing embedded multimedia bitstreams to improve the error resilience of source (compression) codes. This problem is important because of the increasing popularity of embedded compression methodology and its suitability for scalable streaming media over IP or/and mobile IP. We study various packetization schemes against packet erasure at both low and high bit rates. Maximizing packetization efficiency for embedded bitstreams is formulated as a discrete optimization problem and globally optimal packetization (OP) algorithms are proposed under different settings. Suboptimal packetization algorithms are also devised to reduce the complexity of the OP algorithms. In order to assess their effectiveness, the proposed packetization algorithms are used to packetize embedded image and video bitstreams with simulated packet loss. Experimental results show that our OP algorithms slightly outperforms suboptimal ones. In addition to confirming the superiority of the OP algorithms, these results also provide justification of heuristic packetization methods published in the literature.