A variable partition duplex scheme on packet reservation multiple access protocol (VPD-PRMA) is analyzed in this paper. We assume a four-state speech model for a conversational pair and successfully obtain performance measures by approximate Markovian analysis. Analytical results show that they quite fit simulation results; and VPD-PRMA can get higher statistical multiplexing gain than fixed partition duplex (FPD)-PRMA, due to the trunking effect. We further investigate the effect of design parameters of permission probability and enlarged reservation duration on system performance by computer simulation. Simulation results shows that it exists appropriate values for these two design parameters so that the packet dropping probability can be minimized. The adjustment of permission probability can greatly improve the performance of uplink traffic with slight deterioration of the performance of downlink traffic; the provision of enlarged reservation duration scheme can enhance the system performance.

In universal personal telecommunication (UPT) environments, UPT networks retain information related to incall/outcall registration in UPT user service profiles in order to provide incoming UPT calls for UPT users in any location who have registered at a terminal. As UPT networks support incall registration, terminal users can be different from terminal owners, and several UPT users can register for incoming calls on a single terminal. Therefore, appropriate third-party protection procedures are needed to protect the rights of terminal owners. A terminal profile database can be used to store information regarding terminal states and incall UPT users registered on a terminal in order to enable third-party protection procedures. In order to manage information within both the terminal profile and the service profile, we propose a request-based scheme for incall registration/deregistration of UPT users and incall registration resets of terminal owners. We evaluate the performance of the scheme in terms of; 1) total cost and, 2) the number of terminal profile accesses per unit time for a terminal.

We first demonstrate a self-pulsation phenomenon in a semiconductor ring laser(SRL). Not only self-mode-locked optical pulse but self-Q-switched optical pulse can be observed in a SRL. Furthermore, experimental results show that the repetition period of the Q-switched optical pulse train can be controlled by the injection current to a SRL.

Network applications such as FTP, WWW, Mirroring etc. are presently operated with little or no knowledge about the characteristics of the underlying network. These applications could operate more efficiently if the characteristics of the network are known and/or are made available to the concerned application. But network characteristics are hard to come by. The IP Performance Metrics working group (IETF-IPPM-WG) is working on developing a set of metrics that will characterize Internet data delivery services (networks). Some tools are being developed for measurements of these metrics. These generally involve active measurements or require modificationsin applications. Both techniques have their drawbacks. In this work, we show a new and more practical approach of estimating network characteristics. This involves gathering and analyzing the network's experience. The experience is in the form of traffic statistics, information distilled from management related activities and ubiquitously available logs (squid access logs, mail logs, ftp logs etc. ) of network applications. An analysis of this experience provides an estimate of the characteristics of the underlying network. To evaluate the concept we have developed and experimented with a system wherein the network characteristics are generated by analyzing the logs and traffic statistics. The network characteristics are made available to network clients and administrators by Network Performance Metric (NPM) servers. These servers are accessed using standard network management protocols. Results of the evaluation are presented and a framework for efficient operation of network operations, using the network characteristics is outlined.

This letter presents a cryptographic key assignment scheme for dynamic access control in a hierarchy. A scheme for extending a previous cryptographic key assignment scheme to reduce the computation required for key generation and derivation algorithms is also proposed.

This paper proposes a medium access control (MAC) protocol for single-hop WDM star-coupler networks, in which the number of stations is larger than the number of channels and the stations have arbitrary distances to the star coupler. The proposed protocol has one control channel for reserving the slots of data channels and several data channels which are used to transmit traffic. This paper also suggests a scheme that accomplishes load balancing among data channels for arbitrary traffic patterns between stations. Since this load balancing scheme diminishes an influence that traffic patterns have on the performance of the proposed MAC protocol, the proposed system is appropriate for systems which have asymmetric traffic intensity between stations. Throughput and mean message delay of the MAC protocol are analyzed using a discrete time Markov process and a D/G/1 queue with batch arrivals. The numerical results show that the performance is improved as the message length increases, the maximum round-trip propagation delay decreases, and the number of data channels increases.

This paper describes a newly developed FET Coupled Logic (FCL) circuit that operates at very high frequencies with very low supply voltages below 3.3 V. An FCL circuit consists of NMOS source-coupled transistor pairs for current switches, load resistors, emitter followers and current sources that are controlled by a band-gap reference bias generator. The characteristics and performance are discussed by comparing this circuit with other high-speed circuits. The optimal circuit parameters for FCL circuits are also discussed, and the fact is noted that a larger swing voltage enhances the circuit's performance. The simulated delay of a 0.25 µm FCL circuit is less than 15 ps for a 2.5 V power supply, and the simulated maximum toggle frequencies are over 5 GHz and 10 GHz at 2.5 V and 3.3 V power supply, respectively. The simulation results show that FCL circuits achieve the best performance among the current mode circuits, which include ECL circuits, NMOS source-coupled logic circuits. The delay of the FCL circuit is less than half that of an ECL circuit. The maximum toggle frequency of the FCL circuit is about triple that of NMOS source-coupled logic circuit. Because the FCL circuit uses low-cost CMOS-based BiCMOS technologies, its cost performance is superior to ECL circuits that require expensive base-emitter self-aligned processes and trench isolation processes. Using depletion-mode NMOS transistors for current switches can lower the minimum supply voltage for FCL circuits and it is below 1.5 V. The FCL circuit is a promising logic gate circuit for multi-Gbit/s tele/data communication LSIs.

Operation of fiber-grating semiconductor laser (FGL) has been stabilized by using the semiconductor optical amplifier which has a simple slant-waveguide structure. The emission wavelength, which depends on a temperature, shows hysteresis. Employing the directly modulated FGL at 2.5 Gb/s, transmission over 400 km in standard optical fiber has been successfully achieved.

A novel testing-pad placement method has been developed to greatly improve E-beam observability for multi-level wiring LSIs. In the method, testing pads connecting a lower-metal-layer wire with a top-metal-layer electrode are positioned in the design layout, making removal of the insulator unnecessary. The method features i) pad placement in unoccupied areas in mask patterns to avoid increases in chip size, ii) minimized pad size through the use of stacked vias so that the pads can be placed on as many wire nodes as possible, iii) placement as far as possible from the nearby wires to avoid local field effects, and iv) allocation of one testing pad to one circuit node to minimize the number of testing pads. These measures give us a practical pad-placement method, that has little influence on LSI design. It was shown that the proposed method yielded a dramatic improvement of observability from 13-33% to 88-99% in actual layouts of 0.25-µm ASICs with 20k, 120k, and 390k gates. It was also found that local field effects from nearby wires are negligible for almost all the testing pads. This approach will enable the use of E-beam testing on LSIs made with 0.25-µm technology and the even more sophisticated process technologies to come.

Operation of fiber-grating semiconductor laser (FGL) has been stabilized by using the semiconductor optical amplifier which has a simple slant-waveguide structure. The emission wavelength, which depends on a temperature, shows hysteresis. Employing the directly modulated FGL at 2.5 Gb/s, transmission over 400 km in standard optical fiber has been successfully achieved.

Epsilon serializability (ESR) was proposed to relax serializability constraints by allowing transactions to execute with a limited amount of inconsistency (ε-spec). Divergence control algorithms, viewed as extensions of concurrency control algorithms, enable read-only transactions to complete if their inconsistencies do not exceed ε-spec. This paper studies the performance of two-phase locking divergence control (2PLDC) and optimistic divergence control (ODC) algorithms. We develop a central part of the ESR transaction processing system that runs with 2PLDC and ODC. We applied a comprehensive centralized database simulation model to measure the performance. Evaluations are conducted with multi-class workloads where on-line update transactions and long-duration queries progress under various ε-spec. Our results demonstrate that significant performance enhancements are achieved with a non-zero tolerable inconsistency. With sufficient ε-spec and limited system resources, both algorithms result in comparable performance. However, with low resource contention, ODC performs significantly better than 2PLDC. Furthermore, in the range of small ε-spec, the queries committed by ODC have more accurate results than those committed by 2PLDC.

This paper proposes a new framework of managing virtual spaces based on spatial databases as an extension of VRML-based systems. The framework is suitable for treating continuous virtual spaces and for managing the quality of service (QoS) of the virtual spaces depending on user's operations and situations of computer resources. Levels of detail (LoD) of 3D objects is the most important rule for rendering scenes dynamically while managing the QoS. This paper describes a method of managing the QoS depending on the LoD in the form of spatial queries. An advantage of the framework is that spatial databases can incrementally construct virtual spaces in clients using differential descriptions based on VRML, that is, DVRML, proposed in this paper. Dynamic spatial data such as avatar's movement and real-time multimedia data such as videos should be shared by all participants in a virtual space in real time. Our framework can also handle dynamic spatial data by means of real-time updating of some spatial objects in spatial databases as well as static spatial data. We developed some experimental applications based on the framework in order to prove that it is feasible for networked virtual spaces with video components.

The advent of high-speed networks with quality of service guarantees, will enable the deployment of data-server distributed systems over wide-area networks. Most implementations of data-server systems have been over local area networks. Thus it is important, in this context, to study the performance of existing distributed data management protocols in the new networking environment, identify the performance bottlenecks and develop protocols that are capable of taking advantage of the high speed networking technology. In this paper, we examine and compare the scalability of the server-based two-phase locking protocol (s-2PL), and the group two-phase locking protocol (g-2PL). The s-2PL protocol is the most widely used concurrency control protocol, while the g-2PL protocol is an optimized version of the s-2PL protocol, tailored for high-speed wide-area network environments. The g-2PL protocol reduces the effect of the network latency by message grouping, client-end caching and data migration. Detailed simulation results indicate that g-2PL indeed scales better than s-2PL. For example, upto 28% improvement in response time is reported.

In this paper, we present a priority scheduling algorithm at ATM switches with multi-class output buffers in which the service rate of each class buffer is dynamically adjusted. The service rate is computed periodically by a control scheme. We derive the design formulas of the control scheme to ensure that each class buffer occupancy converges to its desired operating point related to QoS requirement. Moreover, through dynamic service rate control in the proposed scheduling algorithm, the available channel capacity can be estimated exactly. It may be used for rate control of ABR traffic and call admission control of the other real-time traffic (CBR, VBR, etc. ).

Space reservation is important in allocating and releasing storage space in DBMSs to support recoverable actions. Since most existing space reservation methods are designed to perform well when few data pages have spaces reserved by more than one transaction, they are not suitable for some of the newly emerging applications, such as workflow and inventory control systems. In these applications, many concurrent transactions frequently insert and delete records into/from a relatively small table. This paper proposes a new space reservation method that performs well for these types of applications by extending the lock control structures to keep detailed and up-to-date information in a reserved state. This paper also shows, by simulation, that the new method performs better than existing ones for applications in which many concurrent transactions frequently insert and delete records into/from a table, and even for applications where data pages rarely have space reserved by more than one transaction.

The OMG have made the trading service one of the basic CORBA services. A specification has been drawn up (OMG RPF5) but seems to have some problems in terms of scalability and complexity. This paper introduces an architecture called Contextual Clustering Using Service Properties (CCUSP) that deals with issues of scalability. It uses a contextual approach to clustering object service offers based on property commonalities. It also handles issues of scalability of trader federation. An ontological approach is to be used, however not covered in this paper. An implementation of the specialisation graph context model is detailed.

With the introduction of ATM technology, service providers around the world have actively engaged in offering high bandwidth services. Currently, services, such as T1/E1, T3/E3 circuit emulation, are made available to large-volume account users. However, more advanced services, such as multimedia applications, have demanded not just high bandwidth but also flexible rate adaptation with quality-of-service (QoS) guarantee. To support the above service requirements, sophisticated network planning and engineering procedures should be taken. In the past few years, we have conducted various researches on developing the engineering strategies for resource control and management to support multi-rate service offering. We have also looked into the design details of connection control and management for achieving the QoS requirement. We considered the service quality of the underlying transport in regard with the QoS management. In this paper, we will outline those results and give an overview description about the proposed framework.

This paper proposes a novel ultra high-speed file server based on a personal computer (PC) to provide the instantaneous delivery of huge files, like movie files, graphic images and computer programs, over high-speed networks. In order to improve the sustained sequential read speed from arrays of hard drives to host memory in the server, two key techniques are proposed: "multi-stage striping (MSS)" and the "sequential file system (SFS)." An experimental file server based on a general-purpose PC is constructed and its performance is measured. The results show that the server offers ultra high read speeds, up to 105Mbytes/s, with just 8 hard drives.

A method is proposed for deriving a traffic characteristics model that can be used to forecast the traffic volume for intelligent telecommunication services. A sort of regression analysis with dummy variables is used to represent the service quantitatively and to construct the traffic characteristics model. Recursive least squares estimation, which is a special case of the Kalman filter, is applied to the traffic characteristics model to forecast the traffic volume. In the proposed modeling and forecasting, qualitative factors representing a certain service attribute are selected and using an information criterion, the model with the best fit is identified as the most suitable forecasting model. Numerical results using practical observation data showed that the proposed method produces an accurate forecast and is thus effective for practical use.

In this paper we present two traffic control approaches, a circuit emulation traffic control (CETC) and an adaptive priority traffic control (APTC) for supporting voice services in ATM networks. Most voice services can be handled as CBR traffic, this causes a lot of wasted bandwidth. Sending voice through VBR (variable bit rate) may be a better alternative, because it allows the network to allocate voice bandwidth on demand. In CETC, the service discipline guarantees the quality of service (QOS) for voice circuits. Through mathematical analysis, we show that CETC features an adequate performance in delay-jitter. Moreover, it is feasible in implementation. We also present an APTC approach which uses a dynamic buffer allocation scheme to adjust the buffer size based on the real traffic need, as well as employs an adaptive priority queuing technique to handle various delay requirements for VBR voice traffic. It provides an adequate QOS for voice circuits in addition to improving the multiplexing gain. Simulation results show that voice traffic get satisfied delay performance using our approaches. It may fulfill the emerging needs of voice service over ATM networks.