Designing control and robotic systems as autonomous decentralized systems introduces a new degree of flexibility in the manufacturing and in the application of such systems. This flexibility is required for the systems to work in environments that are not totally predictable and that can change dynamically. In this paper, we present a new concept for real-time communication that supports this flexibility while still preserving real-time guarantees for hard real-time communication. The concept is designed to work on multiple-access busses. In particular, we consider its application on wireless local area networks and field-busses. The concept addresses requirements of hard-real time, soft real-time and non real-time communication. For this, we extend the TDMA (time- division multiple-access) approach for time-triggered hard-real time communication by the concept of shared channels that support event-triggered communication and coexist with hard real-time channels. A first implementation of concept has been carried out in the context of the CAN-bus.

For cluster systems consisting of multiple processing nodes and shared servers which consist of an on-line and a backup shared server, we propose a hot-standby scheme for shared servers. In this scheme for shared servers, when the on-line shared server receives a command from a node, it sends only an update command and its data identifier to the backup shared server. Both the on-line and the backup shared server execute the update command independently, and the command result of the on-line shared server is identical to that of the backup shared server. When the on-line shared server fails, the backup reconstructs the shared data by using its own shared data and the user data from each node. We evaluated the system recovery time and the performance overhead for this hot-standby scheme. It enables the performance overhead to be ignored, and the system recovery time to be shortened to 20 seconds in cluster systems.

Asynchronous, distributed, decision-making (ADDM) systems constitute a special class of distributed problems and are characterized as large, complex systems wherein the principal elements are the geographically-dispersed entities that communicate among themselves, asynchronously, through message passing and are permitted autonomy in local decision-making. A fundamental property of ADDM systems is stability that refers to their behavior under representative perturbations to their operating environments, given that such systems are intended to be real, complex, and to some extent, mission critical systems, and are subject to unexpected changes in their operating conditions. ADDM systems are closely related to autonomous decentralized systems (ADS) in the principal elements, the difference being that the characteristics and boundaries of ADDM systems are defined rigorously. This paper introduces the concept of stability in ADDM systems and proposes an intuitive yet practical and usable definition that is inspired by those used in Control Systems and Physics. A comprehensive stability analysis on an accurate simulation model will provide the necessary assurance, with a high level of confidence, that the system will perform adequately. An ADDM system is defined as a stable system if it returns to a steady-state in finite time, following perturbation, provided that it is initiated in a steady-state. Equilibrium or steady-state is defined through placing bounds on the measured error in the system. Where the final steady-state is equivalent to the initial one, a system is referred to as strongly stable. If the final steady-state is potentially worse then the initial one, a system is deemed marginally stable. When a system fails to return to steady-state following the perturbation, it is unstable. The perturbations are classified as either changes in the input pattern or changes in one or more environmental characteristics of the system such as hardware failures. Thus, the key elements in the study of stability include steady-state, perturbations, and stability. Since the development of rigorous analytical models for most ADDM systems is difficult, if not impossible, the definitions of the key elements, proposed in this paper, constitute a general framework to investigate stability. For a given ADDM system, the definitions are based on the performance indices that must be judiciously identified by the system architect and are likely to be unique. While a comprehensive study of all possible perturbations is too complex and time consuming, this paper focuses on a key subset of perturbations that are important and are likely to occur with greater frequency. To facilitate the understanding of stability in representative real-world systems, this paper reports the analysis of two basic manifestations of ADDM systems that have been reported in the literature --(i) a decentralized military command and control problem, MFAD, and (ii) a novel distributed algorithm with soft reservation for efficient scheduling and congestion mitigation in railway networks, RYNSORD. Stability analysis of MFAD and RYNSORD yields key stable and unstable conditions.

In cellular systems, autonomous reuse partitioning (ARP) is one of the channel assignment strategy which attains the high spectral efficiency. In the strategy, the movement of mobile stations (MSs) causes the disturbance of reuse partition. Furthermore the smaller cell size causes the spectral efficiency worse. In this paper, we propose a new ARP strategy with reuse partitioning reconstructing, named RP-reconstructing ARP strategy, for microcellular systems. We evaluate the performance of the proposed strategy with blocking rate and forced call termination rate by the computer simulation. The results show that the system with the proposed strategy accommodates 1.5 times as many users as the system with ARP does.

This paper proposes a model checking method for microcomputer programs. To deal with the state explosion problem, we adopt a compositional verification approach. Based on the proposed method, a microcomputer program for a real-life air-conditioner is verified. The program is large enough to cause state explosion. Among fourteen typical properties of the program, five properties are successfully verified by our method.

In this paper, we propose the high-level service architecture supporting multimedia multicast. The proposed architecture specifies network-oriented and lightweight communication management, which includes group management, multiparty call control and multicast connection/multiple connections control. Many of the existing approaches handling multimedia multicast applications are dependent on specific transport technologies, such as the Internet and ATM, and lack effective communication management. On the other hand, our approach defines flexible and extensible communication management that can be applied to a variety of multimedia multicast applications, independently of transport technologies. Our architecture supports the separation of control from a terminal, which enables remote control and control mobility, so that a user can use a multicast service in a more various way. The architecture is overlaid above legacy transport networks so that the existing network protocols are used for connection control. This minimizes the modification to a legacy transport network and enhances the practicality of the architecture. In addition, terminal manager and virtual device concepts are introduced that hide the details of physical devices from an application designer. The architecture consists of several service components that effectively interact with each other on a distributed platform. To verify and evaluate our architecture, we have prototyped the high-level service architecture on a CORBA platform and analyzed the architecture using a simulation.

This paper presents a new design for testing SRAM-based field programmable gate arrays (FPGAs). The original FPGA's SRAM memory is modified so that the FPGA may have the facility to loop the testing configuration data inside the chip. The full testing of the FPGA is achieved by loading typically only one carefully chosen testing configuration data instead of the whole configurations data. The other required configurations data are obtained by shifting the first one inside the chip. As a result, the test becomes faster. This method does not need a large off-chip memory for the test. The evaluation results prove that this method is very effective when the complexity of the configurable blocks (CLBs) or the chip size increases.

Adaptive Agent Oriented Software Architecture (AAOSA) is a new approach to software design based on an agent-oriented architecture. In this approach, agents are considered adaptively communicating concurrent modules that are divided into a "white box" module responsible for communications and learning and a "black box" which is responsible for the independent specialized processes. An AAOSA system is actually parsing input in the interpretation phase. We will show that AAOSA can be applied to the parallel, and distributed parsing of context sensitive languages.

On the Internet, a Quality of Service (QoS) guaranteed services are increasingly being demanded, and the Internet Engineering Task Force (IETF) is developing the specification documents for the QoS services intensively. This overview details the technical rationales underlining the contents of the specification documents developed by the IETF for Differentiated Services (DiffServ)--to provide QoS guarantee services in the large IP networks-- and Policy Framework--to manage DiffServ compliant networks. The IP networks with DiffServ consist of boundary routers and interior routers. These routers are composed of packet classifiers and marker, shaper, and policing function. Many vendors have developed DiffServ-compliant routers with gigabit interfaces. An example of an implementation of a DiffServ-compliant router and a demonstration of a QoS service using this router are presented here. The Policy Framework is expected to be one of the promising management solutions to co-operate with and manage many DiffServ-compliant routers. An experiment that adopts the Policy Framework to a DiffServ compliant network is also outlined.

This paper proposes a new simple method for network measurement. It extracts 6-bit control flags of TCP (Transmission Control Protocol) packets. The idea is based on the unique feature of flag ratios which is discovered by our exhaustive search for the new indexes of network traffic. By the use of flag ratios, one can tell if the network is really congested. It is much simpler than the conventional network monitoring by a network analyzer. The well-known monitoring method is based on the utilization parameter of a communication circuit which ranges from 0% to 100%. One cannot tell the line is congested even if the factor is 100%. 100% means full utilization and does not give any further information. To calculate the real performance of the network, one should estimate the throughput or effective speed of each user. The estimation needs much calculation. Our new method tries to correlate ratios of TCP control flags and network congestion. The result shows the usefulness of this new method. This paper analyzes the reason why the flag ratios show the unique feature.

This paper describes the Profit-Sharing, a reinforcement learning approach which can be used to design a coordination strategy in a multi-agent system, and demonstrates its effectiveness empirically within a coil-yard of steel manufacture. This domain consists of multiple cranes which are operated asynchronously but need coordination to adjust their initial plans of task execution to avoid the collisions, which would be caused by resource limitation. This problem is beyond the classical expert's hand-coding methods as well as the mathematical analysis, because of scattered information, stochastically generated tasks, and moreover, the difficulties to transact tasks on schedule. In recent few years, many applications of reinforcement learning algorithms based on Dynamic Programming (DP), such as Q-learning, Temporal Difference method, are introduced. They promise optimal performance of the agent in the Markov decision processes (MDPs), but in the non-MDPs, such as multi-agent domain, there is no guarantee for the convergence of agent's policy. On the other hand, Profit-Sharing is contrastive with DP-based ones, could guarantee the convergence to the rational policy, which means that agent could reach one of the desirable status, even in non-MDPs, where agents learn concurrently and competitively. Therefore, we embedded Profit-Sharing into the operator of crane to acquire cooperative rules in such a dynamic domain, and introduce its applicability to the realistic world by means of comparing with RAP (Reactive Action Planner) model, encoded by expert's knowledge.

Packet concentrators are used in many high-speed computer communication systems such as fast packet switches. In these systems, the time available for concentration is very short. It is therefore desirable to realize the packet concentrators as hardware chips for fast concentration. The knockout concentrator was proposed for hardware realization. In this paper, we improve this concentrator to reduce the probability of packet loss, and the improved concentrator is called wraparound knockout concentrator. This concentrator has several wraparound paths within it, and it does not require any additional pin per chip. After contention among the packets in a slot, each winner goes to a distinct output, some losers circulate along the wraparound paths for contention in the subsequent slot, and the remaining losers are discarded. In this manner, some losers are not discarded immediately and they still have the chance to go to the outputs in the subsequent slot, thereby reducing the probability of packet loss. We analyze the number of logic gates required and the probability of packet loss. The numerical results show that if the proposed concentrator has a few wraparound paths, the probability of packet loss can already be reduced by orders of magnitude.

Leaky waves have been known for many years in the context of leaky-wave antennas, but it is only within the past dozen years or so that it was realized that the dominant mode on printed-circuit transmission lines used in microwave and millimeter-wave integrated circuits can also leak. Such leakage is extremely important because it may cause power loss, cross talk between neighboring parts of the circuit, and various undesired package effects. These effects can ruin the performance of the circuit, so we must know when leakage can occur and how to avoid it. In most cases, these transmission lines leak only at high frequencies, but some lines leak at all frequencies. However, those lines can be modified to avoid the leakage. This paper explains why and when leakage occurs, and shows how the dominant mode behaves on different lines. The paper also examines certain less well known but important features involving unexpected new physical effects. These include an additional dominant mode on microstrip line that is leaky at higher frequencies, and a simultaneous propagation effect, which is rather general and which occurs when the line's relative cross-sectional dimensions are changed. The final section of the paper is concerned with three important recent developments: (a) the new effects that arise when the frequency is raised still higher and leakage occurs into an additional surface wave, (b) a basic and unexpected discovery relating to improper real modes, which are nonphysical but which can strongly influence the total physical field under the right circumstances, and (c) the important practical issue of how leakage behavior is modified when the circuit is placed into a package.

The purpose of this note is to carry out study on a 3-out-of-4:G warm standby system with nonidentical components. By using Markov model, the general form solution of stationary availability of the system is obtained. Examples are given to illustrate the solutions of transient and stationary availability of such system.

This paper proposes an electronic soccer lottery protocol suitable for the Internet environment. Recently, protocols based on public-key schemes such as digital signature have been proposed for electronic voting systems or other similar systems. For a soccer lottery system in particular, it is important to reduce the computational complexity and the amount of communication data required, because we must expect that a large number of tickets will be purchased simultaneously. These problems can be solved by introducing hash functions as the core of protocol. This paper shows a practical soccer lottery system based on bit commitment and hash functions, in which the privacy of prize-winners is protected and illegal acts by the lottery promoter or lottery ticket shops can be revealed.

The reconfiguration latency defined as the time taken for reconfiguring a system upon failure detection or mode change. We evaluate it quantitatively for backup sparing, which is one of the most popular reconfiguration methods, by investigating the effects of key parameters.

In a decentralised system the problems of fault tolerance, and in particular error recovery, vary greatly depending on the design assumptions. For example, in a distributed database system, if one disregards the possibility of undetected invalid inputs or outputs, the errors that have to be recovered from will just affect the database, and backward error recovery will be feasible and should suffice. Such a system is typically supporting a set of activities that are competing for access to a shared database, but which are otherwise essentially independent of each other--in such circumstances conventional database transaction processing and distributed protocols enable backward recovery to be provided very effectively. But in more general systems the multiple activities will often not simply be competing against each other, but rather will at times be attempting to co-operate with each other, in pursuit of some common goal. Moreover, the activities in decentralised systems typically involve not just computers, but also external entities that are not capable of backward error recovery. Such additional complications make the task of error recovery more challenging, and indeed more interesting. This paper provides a brief analysis of the consequences of various such complications, and outlines some recent work on advanced error recovery techniques that they have motivated.

A per-connection end-to-end call admission control (CAC) problem is solved in this paper to allocate network resources to an input session to guarantee its quality of service (Qos) requirements. In conjunction with the solution of the CAC problem, a traffic descriptor is proposed to describe the loss rate and the delay bound Qos requirements of the connection to be set up as well as the statistical characteristics of the associated input traffic which is modeled as a linear mean function plus a (zero-mean) fractional Brownian motion. The information in the traffic descriptor is sufficient to determine the allocation of channel bandwidth and buffer space to the input traffic in a network which employs leaky bucket shapers and scheduling algorithms to guarantee the Qos requirements. The CAC problem is solved by an iterative algorithm of which there are two stages in each iteration: one is responsible for the search of a candidate end-to-end routing path and the other for the verification of the legitimacy of this candidate path to meet the Qos requirements and for the allocation of resources in such a legitimate path.

Mathematical proof for the equivalent edge currents for physical optics (POEECs) is given for plane wave incidence and the observer in far zone; the perfect accuracy of POEECs for plane wave incidence as well as the degradation for the dipole source closer to the scatterer is clearly explained for the first time. POEECs for perfectly conducting plates are extended to those for impedance plates.

The long spikes have been often recorded at the multiples of the electron cyclotron frequency in the ionograms of the topside sounders observed in low latitudes. There has not been sufficient explanation for the physical cause for occourrence of the long spike so far. Here, by interpreting this phenomenon as receiving the trapped cyclotron harmonic wave, some analyses for the length of spike are done not only from the viewpoint of the sweeping property of the frequency spectrum of the transmitted pulse but also from that of the mutual positional relation between the propagation path and the orbit of the sounder. The cause of forming a single spike and a graphical calculation method for the long spike are proposed, respectively. Thus, the cause and the fine structure of long spike consisting of superposed spikes are clarified.