Discrete-time queueing models have been studied for many years because of their direct applicability in the performance evaluation of digital communication system and networks, where buffers are used to temporarily store information packets which cannot be transmitted instantaneously. In this paper, we investigate the behavior of a discrete-time multiserver buffer system with infinite buffer size. Packets arrive in the system according to a two-state correlated arrival process. The service times of the packets are assumed to be independent and identically distributed according to a geometric distribution. We present an analytical technique, based on the use of generating functions, for the analysis of the system. Explicit expressions are obtained for the mean values, the variances and the tail distributions of the system contents and the packet delay. The influence of the various model parameters on the behavior of the system is shown by means of some numerical examples.

Many P2P lookup services based on distributed hash tables (DHT) have appeared recently. These schemes are built upon overlay networks and ignore distance to the target resources. As a result, P2P lookups often suffer from unnecessarily long routes in the underlay network, which we call overlay dilation. This paper proposes a new scheme for resource routing, called hybrid hierarchical overlay routing, dubbed Hyho. We introduce distance-weighted Bloom filters (dwBFs) as a concise representation of routing information for scattered resources in overlay networks. To further reduce the size of Bloom filters, so that they are linear in the number of distinct resources, Hyho splits overlay networks in accordance with DHT, where each subnetwork has a smaller set of resources and spans the entire network thinly. As a result, Hyho constructs a hierarchical overlay network and routes requests accordingly. Simulation results show that Hyho can reduce overlay dilation to one half that yielded by the Chord lookup service.

It is important to predict serious deterioration of telecommunication quality. This paper investigates predicting such serious events by analyzing only a "short" period (i.e., a "small" amount) of teletraffic data. To achieve this end, this paper presents a method for analyzing the tail distributions of teletraffic state variables, because tail distributions are suitable for representing serious events. This method is based on Extreme Value Theory (EVT), which provides a firm theoretical foundation for the analysis. To be more precise, in this paper, we use throughput data measured on an actual network during daily busy hours for 15 minutes, and use its first 10 seconds (known data) to analyze the tail distribution. Then, we evaluate how well the obtained tail distribution can predict the tail distribution of the remaining 890 seconds (unknown data). The results indicate that the obtained tail distribution based on EVT by analyzing the small amount of known data can predict the tail distribution of unknown data much better than methods based on empirical or log-normal distributions. Furthermore, we apply the obtained tail distribution to predict the peak throughput in unknown data. The results of this paper enable us to predict serious deterioration events with lower measurement cost.

The problem of signal restoration in the presence of observation space noise has been tackled extensively. However, restoration of degraded signals in the presence of signal space noise leads to considerable complexity because it becomes difficult to distinguish between the original signal and the noise. In this paper, a partial projection filter has been devised for the restoration of signals degraded by both the signal space and the observation space noises. A closed form of the proposed filter has been derived and its performance has been verified experimentally.

This paper proposes a Real-Time Compression Architecture (RTCA), which maximizes the efficiency of web services, while reducing the response time at the same time. The developed architecture not only guarantees the freshness of compressed contents but also minimizes the time needed to compress the message, especially when the traffic is heavy.

This development proposes a highly efficient air-conditioning airflow system for a computer-machine room having high-heat-generating equipment using forced-air cooling. The proposed system recirculates room air in the area surrounding equipment back to the cooling supply air supplied from a double floor. The recirculated air is therefore used as cooling air for computers. This system enables the blowing temperature difference of air-conditioner units to be increased, blower capacity to be decreased, and overall efficiency of air-conditioner units to be increased. Here, we have proposed an air-conditioning airflow system that decreases the amount of cooling supply air while ensuring adequate air ventilation for equipment using forced-air cooling, and a design method for achieving this system.

AF service class in Diffserv by realizes minimum bandwidth guarantee with the use of differentiated drop precedence property marked on each packet. In the context of a multiple domains environment, however, QoS of individual flow is not always preserved due to the re-marking behavior forced at the domain boundaries. Focusing on this point, this paper proposes new packet re-marking schemes that can improve the per-flow QoS of AF service traversing multiple domains. The basic concept of the schemes distinguishes packets re-marked to out-of-profile at the domain boundaries from those already marked as out-of-profile at the time of entering the network, and allows the re-marked packet to recover back to in-of-profile, thus regaining its rightful QoS within the networks. The performance of the proposed schemes is evaluated through simulation. The results on UDP flows show the effectiveness of the proposed schemes for reducing packet losses on the flow through multiple domains and preserving fairness between flows. Simulations on TCP flows show that the proposed schemes improve the throughput of the flows through multiple domains. The proposed scheme is especially effective on the transfer time of short TCP flows such as Web traffic, whose throughput is affected more seriously by a single packet loss due to its flow control mechanisms.

With the need and adoption of link aggregation where multiple links exist between two adjacent nodes in order to increase transmission capacity between them, there arise the problems of service guarantee and fair sharing of multiple servers. Although a lot of significant work has been done for single-server scheduling disciplines in the past years, not much work is available for multi-server scheduling disciplines. In this paper, we present and investigate two round robin based multi-server scheduling disciplines, which are Multi-Server Uniform Round Robin (MS-URR) and Multi-Server Deficit Round Robin (MS-DRR). In particular, we analyze their service guarantees and fairness bounds. In addition, we discuss the misordering problem with MS-DRR and present a bound for its misordering probability.

Personal communication service (PCS) networks support the delivery of communication services as the mobile user moves from one region to another. When a mobile user receives a call, the network has to quickly determine its current location. The existing approach suffers from high delay in locating the mobile since the mobile's current location has to be always consulted on the location databases. Caching the location of the remote mobile is useful to reduce this delay. However, the longer the useless record caused by the movement of the mobile remains in a cache, the higher the degradation of cache memory utilization is imposed on a system. In this paper, we propose an efficient caching scheme that a cached record is not allowed to remain over the predefined time, called a time-threshold, in a cache. A long time-threshold may cause to increase the obsoleteness of the cached record. In contrast, a short time-threshold may cause to degrade memory utilization. This paper finds the optimal time-threshold to enlarge cache memory utilization. Also, we provide a unique solution for determining the optimal time-threshold, and study the effects of changing the important parameters of mobility, calling patterns, and network conditions on the optimal time-threshold. Furthermore, we compare the performance of the proposed caching call delivery scheme and the existing call delivery schemes.

The reliability of a 266 nm cw (continuous-wave) solid-state laser under the influence of purge gas was considered. Scatterers on a mirror during long-term operation were ammonium sulfate (NH4SO4). The synthesis of ammonium sulfate was related to the amount of water in the purge gas. UV power decreased by scatterers when the purge was not conducted.

This paper treats the least-squares linear filtering and smoothing problems of discrete-time signals from uncertain observations when the random interruptions in the observation process are modelled by a sequence of independent Bernoulli random variables. Using an innovation approach we obtain the filtering algorithm and a general expression for the smoother which leads to fixed-point, fixed-interval and fixed-lag smoothing recursive algorithms. The proposed algorithms do not require the knowledge of the state-space model generating the signal, but only the covariance information of the signal and the observation noise, as well as the probability that the signal exists in the observed values.

The notion of effective bandwidth provides an elegant and powerful mathematical basis for the provision of QoS-assured services over IP networks. In this paper, we propose a semi-parametric estimator of effective bandwidth, called Gaussian estimator using buffer masurement, for superposition of sources in IP networks. In contrast to most existing proposals concerning the effective bandwidth estimator, our proposal works based on a small set of measurements of the workload in the buffer of a router. We analytically show the property of the proposed estimator with respect to the dependence on the service rate. We provide numerical results to show that our proposed estimator is more accurate than estimators that rely only on the amount of traffic from sources.

Availability of network access "anytime and anywhere" will impose new requirements to presence services - server load sharing and privacy protection. In such cases, presence services would have to deal with sensor device information with maximum consideration of user's privacy. In this paper, we propose FieldCast: peer-to-peer system architecture for presence information exchange in ubiquitous computing environment. According to our proposal, presence information is exchanged directly among user's own computing resources. We illustrate our result of evaluation that proves the feasibility of our proposal.

The partial projection filter gives optimal signal restoration in the presence of both the signal space and the observation space noises. In this paper, the filter has been characterized from the point of view of its signal restoration and noise suppression capabilities. The filter is shown to suppress the noise component in the restored signal while retaining the signal component, thus maximizing the signal-to-noise ratio. Further, a digital implementation of the filter is presented in matrix form in contrast to its original operator based derivation, for practical applications.

Replication to mask the effects of failures is a basic technique for improving reliability of a file system. Consistency control protocols are implemented to ensure the consistency among these replicas. The native token-based mechanism which merely sequences the distributed requests suffered from the poor system utilization due to the lack of dependence checking between writes and management of out-of-ordered requests. Hence, in this paper, by utilizing the idempotent property of NFS and executing ahead most of independent WRITE requests, the new consistency control scheme is proposed to improve the performance of operations and failure recovery. Finally, a numeric case shows the efficiency of the new scheme.

The massively multiplayer online game (MMOG) industry is suffering from huge outgoing traffic from centralized servers. To accommodate this traffic, game companies claim large bandwidth to Internet Data Centers (IDCs), and several months' payment for that bandwidth is likely to even exceed the cost for MMOG servers. In this paper, we propose a MMOG server architecture to reduce outgoing bandwidth consumption from MMOG servers. The proposed architecture distributes some functions of servers to selected clients, and those clients are in charge of event notification to other clients in order to reduce the outgoing traffic from servers. The clients with server functions communicate with each other in peer-to-peer manner. We analyze traffic reduction as a function of cell-daemonable ratio of clients, and the results show that up to 80% of outgoing traffic from servers can be reduced using the proposed architecture when 10% of clients are cell-daemonable.

Location control of grains by µ-Czochralski process with excimer-laser is a powerful tool for realizing high performance single-crystalline Si TFTs (c-Si TFTs). This study reports the behavior of p-channel single-crystalline Si TFTs fabricated inside a location-controlled grain by µ-Czochralski method. Self-aligned p-channel single-crystalline Si TFTs is fabricated with a top gate structure having ECR-PECVD SiO2 as gate insulator. The field effect hole mobility of 250 cm2/Vs and subthreshold swing of 0.29 V/dec. are obtained successfully. Effects of active Si thickness and boron channel doping on the characteristics of the c-Si TFTs were studied.

Next generation wireless networks are expected to support multimedia applications (audio phone, video on demand, video conference, file transfer, etc.). Multimedia applications make a great demand for bandwidth and impose stringent quality of service (QoS) requirements on the wireless networks. In order to provide mobile hosts with high QoS, efficient and better bandwidth reservation is necessary in multimedia wireless networks. This paper presents a novel hybrid dynamic-grouping bandwidth reservation scheme to support QoS guarantees in the next generation wireless networks. The proposed scheme is based on probabilistic resource estimation to provide QoS guarantees for multimedia traffic in cellular networks. We establish several reservation time-sections, called groups, according to the mobility information of mobile hosts (MHs) of each base station (BS). The amount of reserved bandwidth for each BS is dynamically adjusted for each reservation group. We use the hybrid dynamic-grouping bandwidth reservation scheme to decrease the connection-dropping probability (CDP) and connection-blocking probability (CBP), while increasing the bandwidth utilization. The simulation results show that the hybrid dynamic-grouping bandwidth reservation scheme provides less CDP and less CBP, and achieves high bandwidth utilization.

Masqueraders who impersonate other users pose serious threat to computer security. Unfortunately, firewalls or misuse-based intrusion detection systems are generally ineffective in detecting masqueraders. Anomaly detection techniques have been proposed as a complementary approach to overcome such limitations. However, they are not accurate enough in detection, and the rate of false alarm is too high for the technique to be applied in practice. For example, recent empirical studies on masquerade detection using UNIX commands found the accuracy to be below 70%. In this research, we performed a comparative study to investigate the effectiveness of SVM (Support Vector Machine) technique using the same data set and configuration reported in the previous experiments. In order to improve accuracy of masquerade detection, we used command frequencies in sliding windows as feature sets. In addition, we chose to ignore commands commonly used by all the users and introduce the concept of voting engine. Though still imperfect, we were able to improve the accuracy of masquerade detection to 80.1% and 94.8%, whereas previous studies reported accuracy of 69.3% and 62.8% in the same configurations. This study convincingly demonstrates that SVM is useful as an anomaly detection technique and that there are several advantages SVM offers as a tool to detect masqueraders.

A novel Multiple-Valued Field-Programmable VLSI (MV-FPVLSI) architecture using the Multiple-Valued Source-Coupled Logic (MVSCL) is proposed to implement special-purpose processors. An MV-FPVLSI consists of identical cells, which are connected to 8-neighborhood ones. To reduce the complexity of the interconnection block between two cells in an MV-FPVLSI, a bit-serial fine-grain pipeline architecture is introduced which allows single-wire data transmission and as a result, the data-transmission delay becomes very small in comparison with that of a conventional FPGA. To reduce the number of switches in the interconnection block further, a cell, using multiple-valued source-coupled logic circuits, is proposed, where the input currents can be linearly summed just by wiring without using any active devices. Not only the data, but also the control signal can be superposed by linear summation. As a result, no input switch is required which contributes to smaller data transmission delay. Moreover, an arbitrary 2-input logic function can be generated by linear summation of the input currents and threshold operations using these reconfigurable MVSCL circuits. As the MVSCL circuit has high driving capability in comparison with that of an equivalent CMOS circuit, high-speed logic operation is also possible while maintaining low power.