Dynamic Requests Research Articles

Variable neighborhood search for the stochastic and dynamic vehicle routing problem

In this paper, the authors consider the vehicle routing problem (VRP) with stochastic demand and/or dynamic requests. The classical VRP consists of determining a set of routes starting and ending at a depot that provide service to a set of customers. Stochastic demands are only revealed when the vehicle arrives at the customer location; dynamic requests mean that new orders from previously unknown customers can be received and scheduled over time. The variable neighborhood search algorithm (VNS) proposed in this study can be extended by sampling for stochastic scenarios and adapted for the dynamic setting. We use standard sets of benchmark instances to evaluate our algorithms. When applying sampling based VNS, on average we were able to improve results obtained by a classical VNS by 4.39 %. Individual instances could be improved by up to 8.12 %. In addition, the proposed VNS framework matches 32 out of 40 best known solutions and provides one new best solution. In the dynamic case, VNS improves on existing results and provides new best solutions for 7 out of 21 instances. Finally, this study offers results for stochastic and dynamic scenarios. Our experiments show that the sampling based dynamic VNS provides better results when the demand deviation is small, and reduces the excess route duration by 45–90 %.

Dynamic Request Set based Mutual Exclusion Algorithm in MANETs

Mutual Exclusion (ME) problem involves a group of processes, each of which intermittently requires access to the only resource present in the environment. Handling ME problem becomes difficult due to the dynamic nature of the ad hoc environment. This paper presents a token-based solution to ME problem in the mobile ad hoc environment. The proposed token based algorithm is sensitive to link forming and link breaking and thus is suitable for MANET. The algorithm uses the concept of dynamic request set (DRS). As the request set is dynamically updated, the average size of request set is reduced resulting in less number of messages exchanged per critical section. The algorithm satisfies mutual exclusion, starvation freedom, and freedom from deadlock. The present algorithm has been compared with DRS based ME algorithms for static distributed systems. The results show that the concept of DRS in MANETs can be successfully used. Token loss problem has also been handled separately in the present exposition.

Oil Products Distribution Vehicle Routing Problem with Customers' Dynamic Requests Based on Order Neighborhood System

Oil Products Distribution Vehicle Routing Problem with Customers' Dynamic Requests Based on Order Neighborhood System

A Multicast Sparse-Grooming Algorithm Based on Network Coding in WDM Networks

AbstractTo improve the limited number of wavelength utilization and decrease the traffic blocking probability in sparse-grooming wavelength-division multiplexing (WDM) networks, a multicast sparse-grooming algorithm based on network coding (MCSA-NC) is put forward to solve the routing problem for dynamic multicast requests in this paper. In the proposed algorithm, a traffic partition strategy, that the coarse-granularity multicast request with grooming capability on the source node is split into several fine-granularity multicast requests, is designed so as to increase the probability for traffic grooming successfully in MCSA-NC. Besides considering that multiple destinations should receive the data from source of the multicast request at the same time, the traditional transmission mechanism is improved by constructing edge-disjoint paths for each split multicast request. Moreover, in order to reduce the number of wavelengths required and further decrease the traffic blocking probability, a light-tree reconfiguration mechanism is presented in the MCSA-NC, which can select a minimal cost light tree from the established edge-disjoint paths for a new multicast request.

Launch power determination algorithm for dynamic traffic provisioning in mixed-line-rate optical wavelength division multiplexed networks

In transparent mixed-line-rate MLR optical networks, different line rates, on different wavelengths, can coexist on the same fibre. However, along the path, signal experiences various physical layer impairments PLIs, and its quality also degrades. A major factor that affects transmission quality is launch power of the optical signal. On one hand, power must be high enough to ensure less noise at receiver; on the other hand, it must be lower than the limit where PLIs start to distort the signal. Further, high launch power is disruptive to both, the actual lightpath and its neighbours. In this study, we investigate the problem of determining appropriate launch power for provisioning dynamic connection requests in transparent MLR networks. We propose a heuristic that determines the appropriate launch power of a lightpath. The PLI-average PLI-A approach is based on the optical reach of signals, is practical, and can adapt to the needs of network operators. Results show that performances of the proposed approach are better than the existing schemes.

Integrated planning in hybrid courier operations

Purpose– The purpose of this paper is to present the design and evaluation of an integrated system that supports planners and dispatchers to deliver enhanced courier operations. In addition to regular deliveries and pickups, these operations include: first, mass deliveries to be served over a horizon of multiple days; and second, real-time dynamic requests (DRs) to be served within the same service period.Design/methodology/approach– To address the aforementioned challenges, the authors developed an architecture that enhances a typical fleet management system by integrating purpose designed methods. Specifically, the authors plan mass deliveries taking into account typical routes of everyday operations. For planning DRs in real time, the authors propose an efficient insertion heuristic.Findings– The results from testing the proposed optimization algorithms for planning mass deliveries and real-time DRs are encouraging, since the proposed algorithms outperform current practices. Testing in a practical courier environment, indicated that the enhanced planning system may improve significantly operational performance.Research limitations/implications– The proposed optimization algorithm for the dynamic aspect of this problem comprises a heuristic approach that reaches suboptimal solutions of high quality. The development of fast optimal algorithms for solving these very interesting and practical problems is a promising area for further research.Practical implications– The proposed integrated system addresses significant problems of hybrid courier operations in an integrated, balanced manner. The tests showed that the allocation of flexible orders within a three-day time horizon improved the cost per flexible order by 7.4 percent, while computerized routing improved the cost of initial (static) routing by 14 percent. Furthermore, the proposed method for managing DRs reduced the excess cost per served request by over 40 percent. Overall, the proposed integrated system improved the total routing costs by 16.5 percent on average compared to current practices.Originality/value– Both the planning problems and the related solution heuristics address original aspects of practical courier operations. Furthermore, the system integration and the proposed systematic planning contribute to the originality of the work.

Request differentiation in dynamic light-path establishment for WDM routed all optical networks of data centers

Existing routing and wavelength assignment (RWA) solutions try to minimize the blocking rate as the main quality of service (QoS) metric. However, in ultra high-speed all optical interconnection networks of data centers, more important metrics such as network throughput and channel utilization are of interest for network designers. This paper proposes dynamic request buffering routing and wavelength assignment (DRB-RWA) that aims at maximizing the network throughput and total amount of transmitted data in addition to minimizing the blocking rate by proposing a dynamic RWA scheme based on request differentiation. The proposed scheme tries to exploit buffering approach in order to be able to achieve a pseudo static traffic out of a dynamic traffic; and hence, it would be able to differentiate requests in terms of desired metrics. However, conventional dynamic RWA solutions solely aim at minimizing the blocking rate. We evaluate the performance of the proposed algorithm via analytical approach as well as comprehensive simulations to confirm the fact that the network throughput, and therefore, total amount of transmitted data are maximized when the proposed scheme is applied.

Large scale real-time ridesharing with service guarantee on road networks

Urban traffic gridlock is a familiar scene. At the same time, the mean occupancy rate of personal vehicle trips in the United States is only 1.6 persons per vehicle mile. Ridesharing has the potential to solve many environmental, congestion, pollution, and energy problems. In this paper, we introduce the problem of large scale real-time ridesharing with service guarantee on road networks. Trip requests are dynamically matched to vehicles while trip waiting and service time constraints are satisfied. We first propose two scheduling algorithms: a branch-and-bound algorithm and an integer programing algorithm. However, these algorithms do not adapt well to the dynamic nature of the ridesharing problem. Thus, we propose kinetic tree algorithms which are better suited to efficient scheduling of dynamic requests and adjust routes on-the-fly. We perform experiments on a large Shanghai taxi dataset. Results show that the kinetic tree algorithms outperform other algorithms significantly.

Dynamic Request Redirection and Elastic Service Scaling in Cloud-Centric Media Networks

We consider the problem of optimally redirecting user requests in a cloud-centric media network (CCMN) to multiple destination Virtual Machines (VMs), which elastically scale their service capacities in order to minimize a cost function that includes service response times, computing costs, and routing costs. We also allow the request arrival process to switch between normal and flash crowd modes to model user requests to a CCMN. We quantify the trade-offs in flash crowd detection delay and false alarm frequency, request allocation rates, and service capacities at the VMs. We show that under each request arrival mode (normal or flash crowd), the optimal redirection policy can be found in terms of a price for each VM, which is a function of the VM's service cost, with requests redirected to VMs in order of nondecreasing prices, and no redirection to VMs with prices above a threshold price. Applying our proposed strategy to a YouTube request trace data set shows that our strategy outperforms various benchmark strategies. We also present simulation results when various arrival traffic characteristics are varied, which again suggest that our proposed strategy performs well under these conditions.

Receding horizon temporal logic control in dynamic environments

We present a receding horizon method for controlling an autonomous vehicle that must satisfy a rich mission specification over service requests occurring at the regions of a partitioned environment. The overall mission specification consists of a temporal logic statement over a set of static, a priori known requests, a regular expression over a set of dynamic requests that can be sensed only locally, and a servicing priority order over these dynamic requests. Our approach is based on two main steps. First, we construct an abstraction for the motion of the vehicle in the environment by using input–output linearization and assignment of vector fields to the regions in the partition. Second, a receding horizon controller computes local plans within the sensing range of the vehicle such that both local and global mission specifications are satisfied. We implement and evaluate our method through experiments and simulations consisting of a quadrotor performing a persistent surveillance task over a planar grid environment.

Back-End Forwarding Scheme in Server Load Balancing using Client Virtualization

Load balancing can be done at two levels, the HTTP level and the network level. It refers to the distribution of the HTTP request made by the user across the web server in a server cluster and is achieved by various algorithms such as Random Selection, Round Robin, weighted Round Robin etc. At the network level load balancers are used for the purpose of balancing the load. The approach such as DNS forwarding and spraying the load across the servers is very useful and effective at the network level (11)(12). The load balancers receives the request and proxies the destination ip for forwarding the request to the less utilized servers in order to gain better performance. This paper proposes a server load balancing scheme mainly for the webservers by making the limited number of clients to work as a virtual server which are called virtual clients in the webserver network. This approach is done at the HTTP level by forwarding the HTTP request to the nearest and less loaded virtual client. The HTTP request is only forwarded to get the static content in order to save the current bandwidth utilization of the web server and process more dynamic request on the server side. The daemon routine controls the whole process of web server load balancing but it only processes the HTTP requests. The daemon routine only resides on the web server backend. The client virtualization provides a new anti-overloading technique to reduce the access time of the server and to utilize the server resources without any additional cost. The Client Virtualization also provides a better way to utilize the system bandwidth in web server network. clients the web server easily gets overload thus, it's better to migrate (10) (distribute) the load on other available servers too. The server load also has to be distributed so as not to overload the other available servers in the web-server network. The network congestion in system can reason the overloading which prompts break-down of servers. The best possible appropriation of load on the server is carried out by the load balancer. The load balancer is answerable for the equally assigning the requests to the server pool in order to disallow the over-loading of the single server in the web- server system. The load balancing techniques could be exceptionally adequate for the server hubs to process the client's demands. The load balancing strategies helps in minimizing the reaction time and to legitimately use the throughput of the server network. A large number of algorithms are being utilized by the load balancers to verify which server to send the request to. Random choice, round robin, saturation load balancing, load based, least connection and failover load balancing are the algorithms which are being very frequently used by the load balancers to distribute the load. To enhance the load adjust around the servers various parameters, for example server's recent load, recent reaction time and how much traffic it has been recently assigned are taken into account.

Application of Inclinometer in Arch Bridge Dynamic Deflection Measurement

Dynamic deflection measurement is an important component to the bridge loading experiment or health monitoring. Using high-precision inclinometers to test the dynamic deflection is a good method for High-Speed Railway Bridge deflection measurement in this paper, we develop a kind of precision inclinometer which comprehensives the Capacitive sensor technology and the Servo sensor technology and has been called QY inclinometer. We also derive a new theory to calculate deflection based on inclination. Using eleven QY inclinometers and three Cable-Displacement sensors, we have done a comparison dynamic deflection measurement experiment on an arch bridge. Test results indicate: using inclinometers to measure dynamic deflection can achieve the same accuracy with Cable-Displacement sensor which can achieve 0.1 mm accuracy. Therefore, this experiment has proved Using high-precision inclinometers to measure dynamic deflection of bridge can satisfy the dynamic deflection measurement request of high-speed railway bridge. Comparing with other methods of dynamic deflection measurement, using high-precision inclinometers to measure dynamic deflection is very easy to operate, and also do not need find a static reference point. DOI : http://dx.doi.org/10.11591/telkomnika.v12i5.4933

Provisioning of dynamic traffic in mixed-line-rate optical networks with launch power determination

In mixed-line-rate (MLR) networks, different line rates on different wavelengths can coexist on the same fiber. MLR architectures can be built over transparent optical networks, where the transmitted signals remain in the optical domain along the entire path. Along the transparent optical path, a signal experiences various physical layer impairments (PLIs), and its quality degrades as it travels through each optical component. One of the major factors that affect the transmission quality is the launch power of the optical signal. The power must be large enough to ensure noise resiliency at the receiver, but it must be below the limit where fiber nonlinearities distort the signal. Moreover, high launch power is disruptive not only for the actual lightpath itself but also for neighboring lightpaths, and this effect is particularly critical in MLR networks since advanced modulation techniques used for high line rates are highly susceptible to PLIs. In this study, we investigate the problem of determining the appropriate launch power for provisioning of dynamic connection requests in MLR networks. By setting the appropriate launch power for each connection, we aim to maximize the number of established connections. We propose two different heuristics to determine the appropriate launch power of a lightpath. Worst-case best-case average (WBA) is based on optical reach of signal in a transparent optical network. In impairment-aware launch power determination (I-ALPD), current state of the network and impairments are evaluated to determine the launch power. The proposed approaches are practical and can adapt to the needs of network operators. Simulation results show that the performances of the proposed approaches show better results than the existing schemes in terms of blocking probability and bandwidth blocking ratio.

DyCaPPON: Dynamic circuit and packet passive optical network

Dynamic circuits are well suited for applications that require predictable service with a constant bit rate for a prescribed period of time, such as cloud computing and e-science applications. Past research on upstream transmission in passive optical networks (PONs) has mainly considered packet-switched traffic and has focused on optimizing packet-level performance metrics, such as reducing mean delay. This study proposes and evaluates a dynamic circuit and packet PON (DyCaPPON) that provides dynamic circuits along with packet-switched service. DyCaPPON provides (i) flexible packet-switched service through dynamic bandwidth allocation in periodic polling cycles, and (ii) consistent circuit service by allocating each active circuit a fixed-duration upstream transmission window during each fixed-duration polling cycle. We analyze circuit-level performance metrics, including the blocking probability of dynamic circuit requests in DyCaPPON through a stochastic knapsack-based analysis. Through this analysis we also determine the bandwidth occupied by admitted circuits. The remaining bandwidth is available for packet traffic and we conduct an approximate analysis of the resulting mean delay of packet traffic. Through extensive numerical evaluations and verifying simulations we demonstrate the circuit blocking and packet delay trade-offs in DyCaPPON.

Characterizing the scalability of a Web application on a multi‒core server

SUMMARYThe advent of multi‒core technology motivates new studies to understand how efficiently Web servers utilize such hardware. This paper presents a detailed performance study of a Web server application deployed on a modern eight‒core server. Our study shows that default Web server configurations result in poor scalability with increasing core counts. We study two different types of workloads, namely, a workload with intense TCP/IP related OS activity and the SPECweb2009 Support workload with more application‒level processing. We observe that the scaling behaviour is markedly different for these workloads, mainly because of the difference in the performance of static and dynamic requests. While static requests perform poorly when moving from using one socket to both sockets in the system, the converse is true for dynamic requests. We show that, contrary to what was suggested by previous work, Web server scalability improvement policies need to be adapted based on the type of workload experienced by the server. The results of our experiments reveal that with workload‒specific Web server configuration strategies, a multi‒core server can be utilized up to 80% while still serving requests without significant queuing delays; utilizations beyond 90% are also possible, while still serving requests with ‘acceptable’ response times. Copyright © 2014 John Wiley & Sons, Ltd.

SeaHttp: A Resource-Oriented Protocol to Extend REST Style for Web of Things

Web of Things (WoT) makes it possible to connect tremendous embedded devices to web in Representational State Transfer (REST) style. Some lightweight RESTful protocols have been proposed for the WoT to replace the HTTP protocol running on embedded devices. However, they keep the principal characteristic of the REST style. In particular, they support one-to-one requests in the client–server mode by four standard RESTful methods (GET, PUT, POST, and DELETE). This characteristic is however inconsistent with the practical networks of embedded devices, which typically perform a group operation. In order to meet the requirement of group communication in the WoT, we propose a resource-oriented protocol called SeaHttp to extend the REST style by introducing two new methods, namely BRANCH and COMBINE respectively. SeaHttp supports parallel processing of group requests by means of splitting and merging them. In addition SeaHttp adds spatiotemporal attributes to the standard URI for naming a dynamic request group of physical resource. Experimental results show that SeaHttp can reduce average energy consumption of group communication in the WoT by 18.5%, compared with the Constrained Application Protocol (CoAP).

Evaluation of Web Security Mechanisms Using Inline Scenario & Online Scenario

In today's world there is large amount use of computer especially for web application. Most of the people do their transaction through web application. So there are chances of personal data gets hacked then need to be provide more security for both web server and database server. For that double guard system is used. The double guard system is used to detect and prevent attacks using Intrusion detection system.This system prevents attacks and prevents user account from intruder from hacking his/her account. By using IDS, system can provide security for both web server and database server using mapping of request and query. An IDS system that models the network behavior of user sessions across both the front-end web server and the back-end database. This system able to search for in a place (container) attacks that previous Intrusion Detection System (IDS) would not be able to identify. System will try this by isolating the flow of information from each web server session. It quantify the detection accuracy when system attempt to model static and dynamic web requests with the back-end file system and database queries. For static websites, system built a well-correlated model, for effectively detecting different types of attacks. Moreover, system showed that this held true for dynamic requests where both retrieval of information and updates to the back-end database occur using the web- server front end.

Spectrum-efficient optical drop-add-drop network with a centralized multi-carrier light source

Traditional ROADM networks strictly follow the coarse ITU-T standard wavelength grids and channel spacings, which would result in low optical spectrum utilizations under dynamic traffic requests of variable spectrum lightpaths. This paper presents a spectrum-efficient optical drop-add-drop network with a centralized multi-carrier light source (C-MCLS). The C-MCLS generates thousands of optical carriers with uniform and narrow channel spacings. The optical carriers are distributed to each network node as light sources on demand through ROADMs designed with the carrier-drop function. Spectrum-aware optical carrier allocation is studied first in the proposed network. This paper proposes a Minimum Fragmentation Request First (MinFragRF) optical carrier allocation algorithm compared with the Maximum Spectrum Request First (MaxSRF) and Minimum Spectrum Request First (MinSRF) allocation algorithms. This paper also studies how channel spacings of optical carriers impact on the network performance under variable traffic demands. We perform both network analysis and simulations to evaluate the network performance in terms of the lightpath blocking probability (LP_BP) and the effective spectrum efficiency. We analytically derive the formulas of LP_BP and average effective spectrum efficiency in the proposed network. Simulation results show that the proposed network with more narrow channel spacings greatly reduces the lightpath blocking probability compared with the traditional ROADM network. The average effective spectrum efficiency of the proposed network can be improved about 100 % compared with that of the traditional ROADM network by choosing appropriate network design parameters. The MinFragRF allocation algorithm has a better LP_BP performance than that of the MaxSRF and has a better spectrum utilization efficiency than that of the MinSRF. The optimal channel spacing evaluations show that narrow channel spacings such as 6.25 and 12.5 GHz greatly improve LP_BP performance when low bit-rate traffic requests dominate in the traffic model. However, as the high bit-rate traffic requests increase, the performance advantage of narrow channel spacings is gradually disappearing.

Space4time: Optimization latency-sensitive content service in cloud

Nowadays, as cloud service is increasingly a commodity, some Cloud Service Providers (CSPs) make profit by providing content services, and play the more important role of delivering content to users. Providing content services presents new challenges for coordination between storage systems and network infrastructures, specifically for latency-sensitive applications such as voice, video, and terminal services.However, prior research has not applied collaboration techniques of storage and network inline to the request path for latency sensitive applications. In this paper, we propose a latency-sensitive content distribution mechanism, Space4time, for a real world system. We observe that operation is largely affected by the collaboration among end users, storage and networks in cloud. Meanwhile, dynamic request routing within the cloud is strongly coupled with content placement decisions when designing the mechanism. Based on blocking probability, we propose content distribution and request routing strategies that take as input storage and network traffic information. Our strategies enable us to balance storage capacity savings and network traffic for performance, as demonstrated in our YouTube trace-based simulation. Our evaluation shows that Space4time outperforms StaticScheme on average 22.3% for access latency improvement. With more sites, Space4time has a better performance due to reduced traffic.

Optimizing Concurrency Performance of Complex Services in Mobile Environment

Hosting services on mobile devices has been considered as the key solution for domains that have special requirement on portability, timeliness, and flexibility on service deployment. Typical examples include, among many others, military, music, healthcare, gaming, and data sharing. Despite the recent boom of mobile computing makes service deployment in mobile environment possible, significant challenges arise due to the limitations in existing mobile hardware/software capable of managing resource intensive applications. The situation gets worse when managing complex services that allow concurrent clients and requests. This paper addresses the issue related specifically to concurrency control improvement in mobile web servers to support the mobile deployment of complex services. The authors identify key factors that affect a system to respond a request, including request related factors, system resource related factors, and context. Based on this, the authors propose a dynamic heavy request classification model (DHRC) to estimate the heaviness of an incoming request using machine-learning methods. The heavy request will be detected, which requires relatively heavy system resources of the mobile server to generate a response. The authors design a dynamic request management strategy (DRMS), which reduces the number of discarded requests by adding heavy requests to a queue and processing them asynchronously. The proposed solution is implemented on Android-based mobile devices as an extension of I-Jetty web server. Experimental studies are conducted and the result indicates the effectiveness of our solution.