Liang-Teh Lee

A novel call admission control policy using mobility prediction and throttle mechanism for supporting QoS in wireless cellular networks

The decision of call admission becomes an important work owing to the scarce wireless spectrum for wireless cellular networks. If there exists adequate information for call admission control (CAC) schemes, the terms of quality of service (QoS), such as call dropping probability (CDP), call blocking probability (CBP), and system utilization, will be kept in a certain acceptable level. Therefore, a prediction system which can predict most information, such as system utilization and CDP, in advance with a novel data mining technique and a distributed CAC scheme is presented in this paper. Based on the prediction results and the bandwidth consumption of adjacent cells, the proposed CAC scheme is able to decide to admit a new call. The throttle flag that can indicate the usage of current cell is proposed to prevent the newly admitted call request from being blocked in adjacent cells if handoff is needed. The simulation results show that the proposed CAC scheme can maintain the CDP below a predefined threshold, and the CBP is also lower than the cluster prediction and traditional guard channel policies.

Performance issues of grid computing based on different architecture cluster computing platforms

This research paper discusses performance issues of cluster and grid computing platforms, and reasons to support the implementation of these computing infrastructures. A number of benchmark programs are executed in these computing systems, in order to perform performance analysis of experimental results. We are able to show that cluster platforms are excellent alternatives to access to supercomputing, due to its cost/performance, scalability and commodity components factors. In addition, we also show that grid technology is viable by increasing total system performance at no additional cost.

An HMM prediction and throttling-based call admission control scheme for wireless multimedia networks

With the increase in data transmission for wireless networks, multimedia services are gaining popularity in next-generation cellular networks. If the appropriate information exists for Call admission control (CAC) schemes, the terms of quality of service (QoS), such as call dropping probability (CDP), and call blocking probability (CBP) will be kept as low as possible, and higher system utilization can be achieved. Unfortunately, it is difficult to obtain such information owing to user indeterminate mobility. In this paper, the proposed scheme reduces the CDP with a statistical method, called Hidden Markov Models (HMM), that is suitable for solving a dynamic situation has been introduced and applied to the CAC scheme. The prediction of user mobility can be modeled and solved as an optimal-state sequence problem for the HMM. The proposed CAC method that adopts the prediction result of user mobility can reserve appropriate bandwidths for a handoff call in advance, thus, the CDP will be kept below a lower level. Moreover, the throttle flag that indicates the usage of bandwidth in each cell is proposed to prevent the new call request from being dropped in the adjacent cells if handoff is needed, and then the CDP will be further lowered. Besides, the CBP will also be kept relatively low since the proposed method can reserve the suitable bandwidths in the appropriate cells but not reserve stationary ones which are always adopted by traditional CAC methods for each cell. The simulation results show that the proposed method can meet CDP and CBP requirements, and the system utilization can also be improved.

A Dynamic Scheduling Algorithm in Heterogeneous Computing Environments

The grid computing system can support execution of computationally intensive parallel and distributed applications. The main characteristics of grid computing system are similar to the heterogeneous computing system, except the fluctuant transfer rate. A dynamic scheduling algorithm, called dynamic HEFT (DH) algorithm is proposed in this paper to enhance the functions of the original static HEFT (SH) algorithm. Instead of dispatching tasks to physical processors directly, the DH algorithm dispatches tasks to multiple queues. During runtime, the DH algorithm continues to dispatch the scheduled tasks to corresponding physical processor and predicts the transfer rate. Once the difference between two consecutive transfer rates is greater than the threshold value, rescheduling will be performed. The experimental results show that the proposed DH algorithm performs better than the SH algorithm in the system, especially under the grid computing environment, with fluctuant transfer rate and high bandwidth differences

Implementation of visual MPI parallel program performance analysis tool for cluster environments

In this paper, we present visual tool for performance measurement and analysis of MPI parallel programs in cluster environments. Most of tools available today for cluster systems show solely system performance data (e.g., CPU load, memory usage, network bandwidth, machine-room temperature, server average load, among others), being more suitable for system administrators who maintain such system. The visual tool is designed to show performance data of all computer nodes involved in the execution of MPI parallel program, such as CPU load level and memory usage. Additionally, this tool is able to display comparative performance data charts of multiple executions of the application (instrumented with MPI interface) under development.

Applying linux high-availability and load balancing servers for video-on-demand (VOD) systems

In this research paper, we integrate and implement High-Availability (HA) and Load-Balancing technologies to clusters of workstations, increasing both the availability and scalability of services and resources in these systems. The cluster of workstations is commonly built and used as web-based VOD servers. Thus, this paper presents the hardware and software configurations of cluster systems working as VOD servers.

A Cell-based Call Admission Control Policy with Time Series Prediction and Throttling Mechanism for Supporting QoS in Wireless Cellular Networks

Due to the scarce wireless spectrum, the decision of call admission becomes an important work when a mobile call requests for bandwidth in cellular networks. A prediction system which can predict most information, such as system utilization and CDP and a CAC scheme which uses the prediction information generated by the proposed predicted system are proposed in this paper. Our proposed prediction system can provide prediction information in advance, whether the repetitive time series pattern of the information exists or not. A simple scheme that requires less resource has been used to generate prediction values, before the repetitive patterns have been found. The proposed CAC scheme is based on the prediction results and the bandwidth consumptions in the adjacent cell for deciding to admit a new call or not. The throttle flag that indicates the usage of current cell is proposed to prevent the newly admitted call request being blocked in the adjacent if handoff needed. In order to simplify the complexity of implementation and avoid computations being extremely riveted on the mobile switch center (MSC), an agent which consists of the prediction module and the CAC algorithm is implemented in each cell, and the statistics of each agent can be gathered and analyzed by the central unit. The simulation results show that the proposed CAC scheme can maintain CDP below a predefined threshold, and the CBP is lower than traditional guard channel policies

An extenics-based load balancing mechanism for distributed computing systems

In distributed computing systems, load balancing is one of the most important factors that affect the system performance. This paper presents sender-initiated dynamic load balancing policies in a distributed computing system. There are four policies consisted in the proposed extenics-based load. balancing mechanism (ELBM). For the transfer policy, instead of defining a fixed threshold value in the traditional load balancing policies, we apply the extension set theory and use the average response time of jobs as a factor to create an adaptive threshold value which is calculated by a relational function of average response time, for determining that a new arriving job should be migrated or not. In addition to the transfer policy, a bypass-transfer method is used in the location policy. Jobs that need to be migrated do not need to be transferred to central node first, but are transferred to destination node directly. so as to reduce the communication costs. In order to make the system more reliable, a template queue is added at the master node of the system to reduce the job arrival failure. A simulation model has been built for evaluating the performance of the system. Compared with other load balancing mechanisms, such as RT and ALBCII algorithms, the simulation results show that a better performance can be achieved by the proposed mechanism.

Design and Implementation of a PC-Cluster Based Video-On-Demand Server

The video-on-demand (VOD) is one of the most potential services of internet applications. In this paper, a load balanced PC-Cluster for implementing the VOD server has been proposed to offer the video-information to users efficiently. In the proposed scheme, two-Tier model has been adopted in the systematic architecture. The PC-Cluster is used to be the storage system of the VOD server and the load balancing mechanism in the proposed system is based on the Least-Connection-First algorithm. For enhancing the sharing and balancing of the system load among video servers in the cluster, a video placement strategy has also been proposed. Accompany with the dynamically adjusted files in each video level, a dynamical cyclical video replacement mechanism is applied to replicate and allocate video files for improving the load balance of the system. From the experimental results, we can see that a better load balance of the system can be achieved by applying the proposed scheme.

A Dynamic Reservation and Call Admission Control Policy with HMM for Multimedia Cellular Networks

The multimedia services are getting to become the major trend in next-generation cellular networks. Call admission control (CAC) plays the key role for guaranteeing the quality of service (QoS) in cellular networks. The goal which keeps both the call dropping probability (CDP) and call blocking probability (CBP) as low as possible is more difficult owing to the user indeterminate mobility. In this paper, the hidden Markov models (HMM) concept which is suitable for solving a dynamic situation is introduced and applied to the call admission control policy. The prediction of user mobility can be modeled and resolved as a decoding problem for the HMM. According to the prediction result, the proposed CAC method can reserve appropriate bandwidths for a handoff call beforehand, thus the call dropping probability is almost the same as the traditional guard channel policies that can keep lower CDP than unpredicted ones, moreover, the call blocking probability is also lower than the traditional guard channel policies since the proposed method can reserve the suitable bandwidths in the appropriate cells but not reserve a stationary ones which are always adopted by traditional CAC methods. Therefore, the proposed method can not only satisfy both CDP and CBP issues, but also improve the system utilization