Server Problem Research Articles

Fast heuristics for the time‐constrained immobile server problem

AbstractWe propose easy‐to‐implement heuristics for time‐constrained applications of a problem referred to in the literature as the facility location problem with immobile servers, stochastic demand, and congestion, the service system design problem, or the immobile server problem (ISP). The problem is typically posed as one of allocating capacity to a set of M/M/1 queues to which customers with stochastic demand are assigned with the objective of minimizing a cost function composed of a fixed capacity‐acquisition cost, a variable customer‐assignment cost, and an expected‐waiting‐time cost. The expected‐waiting‐time cost results in a nonlinear term in the objective function of the standard binary programming formulation of the problem. Thus, the solution approaches proposed in the literature are either sophisticated linearization or relaxation schemes, or metaheuristics. In this study, we demonstrate that an ensemble of straightforward, greedy heuristics can rapidly find high‐quality solutions. In addition to filling a gap in the literature on ISP heuristics, new stopping criteria for an existing cutting plane algorithm are proposed and tested, and a new mixed‐integer linear model requiring no iterating algorithm is developed. In many cases, our heuristic approach finds solutions of the same or better quality than those found by exact methods implemented with expensive, state‐of‐the‐art mathematical programming software, in particular a commercial nonlinear mixed‐integer linear programming solver, given a five‐minute time limit.

Stalling in Queuing Systems with Heterogeneous Channels

The present paper considers a model of stalling in a queueing system (QS) with any number of different capacities of heterogeneous servers. The state graph and the corresponding linear system for steady-state probabilities are derived using the standard Markov chain technique. The obtained solution of the steady-state probabilities model is numerically stable; the complexity of the corresponding expressions does not depend on the number of QS states; thus, they enable us to analytically study the QS characteristics. Optimization of a stalling buffer is considered as well, and it is shown that stalling helps us to solve the slow server problem under an appropriate choice of stalling buffer size, making the slow servers usable under various values of system load. The asymptotic conditions of optimal query distribution in channels, when the ratio of the capacities of the fast and slow servers is increasing, are also established. Moreover, some applications of the developed model in heterogeneous server clusters and in work productivity modelling for forest harvesting applications are discussed.

Breaking the 2-competitiveness barrier for two servers in a tree

A randomized on-line algorithm is given for the 2-server problem on a tree, with competitiveness less than 1.94 against the oblivious adversary. This is the first algorithm for this problem with competitive ratio less than 2. The algorithm generalizes earlier work for the line using fractional analysis, and defines a potential in terms of isolation indices from T-theory.

Blockchain and PUF-Based Lightweight Authentication Protocol for Wireless Medical Sensor Networks

Due to the emergence of heterogeneous Internet of Medical Things (IoMT) (e.g., wearable health devices, smartwatch monitoring, and automated insulin delivery systems), large volumes of patient data are dispatched to central cloud servers for disease analysis and diagnosis. Although this direct mode brings a lot of convenience for both patients and medical professionals (MPs), the open communication channel between them also incurs several security and privacy issues, such as man-in-the-middle attacks, eavesdropping attacks, and tracking attacks. Based on the unsolved challenges in wireless medical sensor networks (WMSNs), several researchers have proposed various authentication and key agreement (AKA) protocols for this type of healthcare system recently. However, most of these protocols do not perceive physical-layer security and over-centralized server problem in WMSN. In this article, to address these two open problems, we propose a lightweight and reliable authentication protocol for WMSN, which is composed of cutting-edge blockchain technology and physically unclonable functions (PUFs). In addition, a fuzzy extractor scheme is introduced to deal with biometric information. Subsequently, two security evaluation methods are used to prove the high reliability of our proposed scheme. Finally, performance evaluation experiments illustrate that the proposed mutual authentication protocol requires the least computation and communication cost among the compared schemes.

The Infinite Server Problem

We study a variant of the k -server problem, the infinite server problem, in which infinitely many servers reside initially at a particular point of the metric space and serve a sequence of requests. In the framework of competitive analysis, we show a surprisingly tight connection between this problem and the resource augmentation version of the k -server problem, also known as the (h,k) -server problem, in which an online algorithm with k servers competes against an offline algorithm with h servers. Specifically, we show that the infinite server problem has bounded competitive ratio if and only if the (h,k) -server problem has bounded competitive ratio for some k = O ( h ). We give a lower bound of 3.146 for the competitive ratio of the infinite server problem, which holds even for the line and some simple weighted stars. It implies the same lower bound for the (h,k) -server problem on the line, even when k/h → ∞, improving on the previous known bounds of 2 for the line and 2.4 for general metrics. For weighted trees and layered graphs, we obtain upper bounds, although they depend on the depth. Of particular interest is the infinite server problem on the line, which we show to be equivalent to the seemingly easier case in which all requests are in a fixed bounded interval. This is a special case of a more general reduction from arbitrary metric spaces to bounded subspaces. Unfortunately, classical approaches (double coverage and generalizations, work function algorithm, balancing algorithms) fail even for this special case.

The Electronic Registration of Liability Rights

This research aims to examine the inhibiting factor of electronic mortgage registration procedures. The type of this research is empirical normative legal research by using the statutory, conceptual and empirical approach. The result shows that the electronic registration of mortgage performed through several steps, namely: (1) login to the application of electronic land services; (2) choosing the mortgage service on the menu bar; (3) submit an application to make a mortgage file; (4) completing the entry; (5) uploading the necessary documents; (6) confirming file; (7) paying a deposit order for the security rights registration; (8) recording and issuance of mortgage certificate. While the inhibiting factors on the electronic registration of mortgages are: (a) there is some official land registrar (in short term known as PPAT) who do not understand the registration procedures of electronic mortgage rights services. (b) the PPAT has not validated and registered their data in the PPAT Partner application at mitra.atrbpn.go.id; (c) the creditors have not validated and registers in the financial services partners application at mitra.atrbpn.go.id (d) the certificate of land rights has not been validated which will be used as the object to grant a mortgage right. Before the deed of mortgage rights granted, at the time of the checking the PNBP can only be paid a day after the validation completed; (e) the server problem which often occurred when uploading the requirements and the deed documents; (f) the required documents for filing a mortgage rights application are not complete.

The Policy on Law Enforcement of Illegal Sand Mining In Special Region of Yogyakarta

This research aims to examine the inhibiting factor of electronic mortgage registration procedures. The type of this research is empirical normative legal research by using the statutory, conceptual and empirical approach. The result shows that the electronic registration of mortgage performed through several steps, namely: (1) login to the application of electronic land services; (2) choosing the mortgage service on the menu bar; (3) submit an application to make a mortgage file; (4) completing the entry; (5) uploading the necessary documents; (6) confirming file; (7) paying a deposit order for the security rights registration; (8) recording and issuance of mortgage certificate. While the inhibiting factors on the electronic registration of mortgages are: (a) there is some official land registrar (in short term known as PPAT) who do not understand the registration procedures of electronic mortgage rights services. (b) the PPAT has not validated and registered their data in the PPAT Partner application at mitra.atrbpn.go.id; (c) the creditors have not validated and registers in the financial services partners application at mitra.atrbpn.go.id (d) the certificate of land rights has not been validated which will be used as the object to grant a mortgage right. Before the deed of mortgage rights granted, at the time of the checking the PNBP can only be paid a day after the validation completed; (e) the server problem which often occurred when uploading the requirements and the deed documents; (f) the required documents for filing a mortgage rights application are not complete.

Managing Multiple Mobile Resources

We extend the Mobile Server problem introduced in Feldkord and Meyer auf der Heide (TOPC 6(3), 14:1–14:17 2019) to a model where k identical mobile resources, here named servers, answer requests appearing at points in the Euclidean space. To reduce communication costs, the positions of the servers can be adapted by a limited distance ms per round for each server. The costs are measured similarly to the classical Page Migration problem: i.e., answering a request induces costs proportional to the distance to the nearest server, and moving a server induces costs proportional to the distance multiplied with a weight D. We show that, in our model, no online algorithm can have a constant competitive ratio: i.e., one which is independent of the input length n, even if an augmented moving distance of (1 + δ)ms is allowed for the online algorithm. Therefore we investigate a restriction of the power of the adversary dictating the sequence of requests: We demand locality of requests: i.e., that consecutive requests come from points in the Euclidean space with distance bounded by some constant mc. We show constant lower bounds on the competitiveness in this setting (independent of n, but dependent on k, ms and mc). On the positive side, we present a deterministic online algorithm with bounded competitiveness when an augmented moving distance and locality of requests is assumed. Our algorithm simulates any given algorithm for the classical k-Page Migration problem as guidance for its servers and extends it by a greedy move of one server in every round. The resulting competitive ratio is polynomial in the number of servers k, the ratio between mc and ms, the inverse of the augmentation factor 1/δ and the competitive ratio of the simulated k-Page Migration algorithm. We also show how to directly adapt the Double Coverage algorithm (Chrobak et al. SIAM J. Discrete Math. 4(2), 172–181 11) for the k-Server problem to receive an algorithm with improved competitiveness on the line.

5G Network Performance by Cell-Edge Servers Optimization Assignment (5GNP-CESOA)

With the rapid increased growth of Internet of Things (IoT) and 5G networks in smart cities, big data can be generated, resulting in higher latency for the conventional cloud computing model. To enhance users experience, commodity servers were built at the edges of decentralized networks of mini data centers serving regions. Our paper deals with this problem, in purposes of making a total cost optimization assignment cell to servers in Edge computing network where a so-called meta-heuristic (MH) optimization method was chosen. The first task of the present work is devoted to different methods used in server’s Edge placement network optimization including MH methods. Second, the cell assignment to Edge server problem is formulated. The third task is taken up by developing a Tabu Search (TS) application (of fourteen cells network and three Edge servers as a quasi-optimal procedure) for total costs of networks, simulated under MATLAB software. As perspectives, the results compared with other MH methods should be validated, and the server capacity and traffic constraints for each cell have to be added.

Multiple Server SRPT With Speed Scaling Is Competitive

Can the popular shortest remaining processing time (SRPT) algorithm achieve a constant competitive ratio on multiple servers when server speeds are adjustable (speed scaling) with respect to the flow time plus energy consumption metric? This question has remained open for a while, where a negative result in the absence of speed scaling is well known. The main result of this paper is to show that multi-server SRPT with speed scaling can be constant competitive, with a competitive ratio that only depends on the power-usage function of the servers, but not on the number of jobs/servers or the job sizes (unlike when speed scaling is not allowed). When all job sizes are unity, we show that round-robin routing is optimal and can achieve the same competitive ratio as the best known algorithm for the single server problem. Finally, we show that a class of greedy dispatch policies, including policies that route to the least loaded or the shortest queue, do not admit a constant competitive ratio. When job arrivals are stochastic, with Poisson arrivals and i.i.d. job sizes, we show that random routing and a simple gated-static speed scaling algorithm achieves a constant competitive ratio.

The Mobile Server Problem

We introduce the Mobile Server problem, inspired by current trends to move computational tasks from cloud structures to multiple devices close to the end user. An example of this is embedded systems in autonomous cars that communicate to coordinate their actions. Our model is a variant of the classical Page Migration problem. More formally, we consider a mobile server holding a data page. The server can move in the Euclidean space (of arbitrary dimension). In every round, requests for data items from the page pop up at arbitrary points in the space. The requests are served, each at a cost of the distance from the requesting point and the server, and the mobile server may move, at a cost D times the distance traveled for some constant D . We assume a maximum distance m that the server is allowed to move per round. We show that no online algorithm can achieve a competitive ratio independent of the length of the input sequence in this setting. Hence, we augment the maximum movement distance of the online algorithms to (1+&delta) times the maximum distance of the offline solution. We provide a deterministic algorithm that is simple to describe and works for multiple variants of our problem. The algorithm achieves almost tight competitive ratios independent of the length of the input sequence. Our algorithm also achieves a constant competitive ratio without resource augmentation in a variant where the movement of clients is also restricted.

Stalling for solving slow server problem

The model of stalling in queueing system (QS) with two heterogeneous severs is considered, the probabilities of steady states by means of Tchebyshev polynomials of second order are derived. The obtained expressions are stable numerically, their complexity does not depend on the number of states, and they enable us to study QS characteristics analytically. Optimization of a stalling buffer is considered as well and it was shown that stalling helps us to solve the slow server problems under an appropriate choice of stalling buffer size, making a slow server usable under various values of system load. Asymptotic conditions of optimal query distribution in servers are established, when the ratio of capacities of fast and slow channels is increasing. Application of the model developed in computer networks is discussed as well.

The ( h,k )-Server Problem on Bounded Depth Trees

We study the k -server problem in the resource augmentation setting, i.e., when the performance of the online algorithm with k servers is compared to the offline optimal solution with h ≤ k servers. The problem is very poorly understood beyond uniform metrics. For this special case, the classic k -server algorithms are roughly (1+1/ϵ)-competitive when k =(1+ϵ) h , for any ϵ > 0. Surprisingly, however, no o ( h )-competitive algorithm is known even for HSTs of depth 2 and even when k / h is arbitrarily large. We obtain several new results for the problem. First, we show that the known k -server algorithms do not work even on very simple metrics. In particular, the Double Coverage algorithm has competitive ratio Ω ( h ) irrespective of the value of k , even for depth-2 HSTs. Similarly, the Work Function Algorithm, which is believed to be optimal for all metric spaces when k = h , has competitive ratio Ω ( h ) on depth-3 HSTs even if k =2 h . Our main result is a new algorithm that is O (1)-competitive for constant depth trees, whenever k =(1+ϵ) h for any ϵ > 0. Finally, we give a general lower bound that any deterministic online algorithm has competitive ratio at least 2.4 even for depth-2 HSTs and when k / h is arbitrarily large. This gives a surprising qualitative separation between uniform metrics and depth-2 HSTs for the ( h , k )-server problem.

Value Iteration Proof of the Three-Server Heterogeneous Server Problem

We study a three-server queueing system where servers are heterogeneous in terms of their service speed. The goal of the system operator is to find an optimal routing strategy, which assigns each customer to a server, in order to minimize all customers' expected sojourn time in the system. Using a value iteration approach, we establish that the optimal routing policy is of a threshold type. In addition, suppose the service speed of server-1 is greater than that of server-2 which is greater than that of server-3, it is found that the optimal routing threshold of server-2 when server-3 is busy, is no greater than the optimal routing threshold of server-3 or that of server-2 when server-3 is idle. Finally, we employ numerical experiments to demonstrate sensitivity analysis.

A Comparative Study in Online Movie Ticket Booking System

Due to increase in technology and digitalization online movie system has become much more popular. Instead of wasting time in queues of movie counter, it provides easy and efficient way to book the tickets online. It is quite fascination to sit at home browses the movies which have been released, read the review and then book the tickets according to our feasibility. Movie booking system is actually in action for the last 15 years but it gained its popularity after 2004 and its reach increased several folds in the past 6–10 years because of increasing net accessibility. In the proposed research paper we have sorted out some of the major issues related to online movie management system. Due to increased traffic server problem and transaction failure are the major problems with online movie booking system. To sort out these Node JS and Mongo DB connectivity has been used. Also, there are some more features which have been addend and are new to movie booking system like mailing the review and trailer of the movie to the user while they book the ticket and showing the view of screen from different orientation of screen. For some trustworthy review we have designed our own questionnaire so that it can give exact view of what is the true review of movie. These reviews will cross checked by the editorial team and then published on the web site. So basically it¶s an advanced version of online movie booking system in which few new features has been added as well as the problems with previous system has been rectified.

R–LINE: A better randomized 2-server algorithm on the line

A randomized on-line algorithm is given for the 2-server problem on the line, with competitiveness less than 1.901 against the oblivious adversary. This improves the previously best known competitiveness of 15578≈1.987 for the problem. The algorithm uses a new approach and defines a potential in terms of isolation indices from T-theory.

On the Advice Complexity of the k-server Problem Under Sparse Metrics

We consider the k-Server problem under the advice model of computation when the underlying metric space is sparse. On one side, we introduce ź(1)-competitive algorithms for a wide range of sparse graphs. These algorithms require advice of (almost) linear size. We show that for graphs of size N and treewidth ź, there is an online algorithm that receives O (n(log ź + log log N))* bits of advice and optimally serves any sequence of length n. We also prove that if a graph admits a system of μ collective tree (q, r)-spanners, then there is a (q + r)-competitive algorithm which requires O (n(log μ + log log N)) bits of advice. Among other results, this gives a 3-competitive algorithm for planar graphs, when provided with O (n log log N) bits of advice. On the other side, we prove that advice of size Ω(n) is required to obtain a 1-competitive algorithm for sequences of length n even for the 2-server problem on a path metric of size N ź 3. Through another lower bound argument, we show that at least n2(logźź1.22)$\frac {n}{2}(\log \alpha - 1.22)$ bits of advice is required to obtain an optimal solution for metric spaces of treewidth ź, where 4 ≤ ź < 2k.

Mixed integer programming formulations for the Biomass Truck Scheduling problem

In this paper, we introduce the Biomass Truck Scheduling (BTS) problem that originated in a real-life herbaceous biomass supply chain (HBSC) around Pecs, Hungary. BTS can be considered as a Parallel Machine Scheduling with a Single Server problem, where identical trucks (parallel machines) deliver biomass from satellite storage locations to a central biorefinery operating a single unloader (single server). We make two particular assumptions regarding the server: the server operation has a unit time length for each trip and idle periods are not allowed for it (server no idle time constraint). We consider two objective functions associated with the revealed HBSC logistic cost structure. First, the number of trucks is minimized (resource availability cost) following which the total truck idle time is minimized. Three mixed integer programming formulations are constructed to solve BTS, and their efficiency is evaluated using a number of test cases. We found that, even if the number of trucks is locked at its minimum value, there is always a schedule with zero truck idle time—that is, there is no trade-off between these two objective functions.

Automatic Backup System for Virtualization Environment

Virtualization is a technology lately much discussed and considered as the proper way to cut costs in the construction of a data center. One example of the implementation of virtualization technologies is to using VMware. Another tools for virtualization are Xen and OpenVZ, but VMware is more flexible than Xen or OpenVZ because VMware can run a variety of operating systems. Although it has the advantage, virtualization technology also has a vital weakness, virtualization technologies could be analogous by putting all the eggs in a basket. This means that if the master server problem, all systems inside the virtual machine can not be used. However, it can be anticipated by provide backup facilities that run continually and automatically. VMware itself has had an application to backup/replicate virtual machines. However, that application is not free yet.This research has been design and creates a web-based software forbacking up virtual machines on VMware. So it made easier for users and admins to perform periodic backups of virtual machines. From the test results has been done, it can be seen that used disk type thin or zeroed thick make process backup faster, system can’t work well when virtual machine has snapshot, scheduling system and restoring system has worked well, physical ability data storage influence system.Keywords: Virtual machine, virtualization, Vmware, Backup, Data Center.

A Comparison of Performance Measures for Online Algorithms

This paper provides a systematic study of several proposed measures for online algorithms in the context of a specific problem, namely, the two server problem on three colinear points. Even though the problem is simple, it encapsulates a core challenge in online algorithms which is to balance greediness and adaptability. We examine Competitive Analysis, the Max/Max Ratio, the Random Order Ratio, Bijective Analysis and Relative Worst Order Analysis, and determine how these measures compare the Greedy Algorithm, Double Coverage, and Lazy Double Coverage, commonly studied algorithms in the context of server problems. We find that by the Max/Max Ratio and Bijective Analysis, Greedy is the best of the three algorithms. Under the other measures, Double Coverage and Lazy Double Coverage are better, though Relative Worst Order Analysis indicates that Greedy is sometimes better. Only Bijective Analysis and Relative Worst Order Analysis indicate that Lazy Double Coverage is better than Double Coverage. Our results also provide the first proof of optimality of an algorithm under Relative Worst Order Analysis.