Session length and group size are two most significant factors in achieving efficient scheduling for unicast and multicast traffic in single-hop wavelength division multiplexing (WDM) local area networks (LANs). This paper presents a hybrid protocol to schedule both unicast and multicast traffic in broadcast WDM networks. The protocol makes an important assumption that unicast traffic is the major portion of the overall traffic and is usually scheduled with a pre-allocation-based protocol. On the other hand, multicast traffic is a smaller portion of the overall traffic with multicast sessions and multicast groups, and is scheduled with a reservation-based protocol. The concept of multicast threshold, a function of random variables including the multicast session length and the multicast group size, is also proposed to partition the multicast traffic into two types. If the transmission threshold of a multicast request is larger than the multicast threshold, the request is handled with a reservation-based protocol. Otherwise, the multicast request is handled similar to unicast traffic; that is, each packet in the multicast session is replicated and sent to the unicast queues of destinations. The results show that the hybrid protocol can achieve better channel utilization efficiency and packet delay for unicast traffic under the multicast scenarios with moderate session length and group size. However, separate scheduling or broadcasting will be more suitable for a multicast scenario with very large session length and group size, which is not common on most realistic networks.

Although a number of car-traffic simulators have been developed for various purposes, none of the existing simulators enhance the simulation accuracy using sensor data or allow the system structure to re-configure the system structure depending on the application. Our goal was to develop a highly accurate, highly modular, flexible, and scalable micro-model car-traffic simulation system. The HLA (High Level Architecture) was applied to every system module as a standard interface between each module. This allows an efficient means for evaluating and validating a variety of micro-model simulation schemes. Our ongoing projects consist of running several identical simulations concurrently, with different parameter sets. By sending the results of these simulations to a manager module, which analyzes both the parameter sets and the simulated results, the manager module can evaluate the best-simulated results and determine the next action by comparing these results with the sensor data. In this system, the sensor data or the statistical data on the flow of traffic, obtained by monitoring real roads, is used to improve the simulation accuracy. Future systems are being planned to employ real time sensor data, where the input of the data occurs at almost real time speed. In this paper, we discuss the design of a HLA-based car-traffic simulation system and the construction of a sensor-data fusion algorithm. We also discuss our preliminary evaluation of the results obtained with this system. The results show that the proposed fusion algorithm can adjust the simulation accuracy to the logged sensor data within a difference of 5% (minimum 1.5%) in a specific time period. We also found that simulations with 500 different parameter sets can be executed within 5 minutes using 8 simulator modules.

We propose knockout ATM switches with two speedup factors under non-uniform traffic with variable hot-spot ports in order to handle flexibly when the number and port of hot-spot change. The proposed models have a function that the maximum cell transmission number called a speedup factor L2 is set to be large when the arrival cells are more than L1. By using this function, it is useful to decrease the cell loss probability of hot-spot ports. First, we propose a knockout ATM switch with two speedup factor in order to reduce the number of accesses from a concentrator to a parallel buffer as a proposed model 1. Moreover, we propose a shared knockout ATM switch in order to decrease the switch elements as a proposed model 2. We evaluate the cell loss probability by means of computer simulations and numerical calculations. As a result, we show that the proposed model 2 satisfy the reqirement of the cell loss probability due to contention at outoput of a batcher network with decreasing the hardware.

The Next Generation Internet Initiative was launched in the U.S. to advance key networking technologies that will enable a new wave of applications on the Internet. Now, in its third year, the program has launched and fostered over one hundred new research projects in partnership with academic, industrial and government laboratories. One key research area that has been emphasized within the program is the next-generation optical networking. Given the ever increasing demand for network bandwidth, and the recent phenomenal advances in WDM technologies, the Next Generation Internet is expected to be an IP-based optical WDM network. As IP over WDM networking technologies mature, a number of important architectural, management and control issues have surfaced. These issues need to be addressed before a true Next Generation Optical Internet can emerge. This paper provides a brief introduction to the overall goals and activities of DARPA's NGI program and describes the key architectural, management, and control issues for the Optical Internet. We review the different IP/WDM networking architectural models and their tradeoffs. We outline and discuss several management and control issues and possible solutions related to the configuration, fault, and performance management of IP over dynamic WDM networks. We present an analysis and supporting simulation results demonstrating the potential benefits of dynamic IP over WDM networks. We then discuss the issues related to IP/WDM traffic engineering in more detail, and present the approach taken in the NGI SuperNet Network Control and Management Project funded by DARPA. In particular, we motivate and present an innovative integrated traffic-engineering framework for re-configurable IP/WDM networks. It builds on the strength of Multi-Protocol Label Switching (MPLS) for fine-grain IP load balancing, and on the strength of Re-configurable WDM networking for reducing the IP network's weighted-hop-distance, and for expanding the bottleneck bandwidth.

This paper describes experimental results of the IP traffic condition based dynamic optical path allocation network system. In the system, optical paths are dynamically allocated between congested node pairs to cope with traffic fluctuations. It seems that this experiment is the first of its kind in the world.

This paper presents a Path Bandwidth Management (PBM) model for large-scale networks that leads to an almost optimal PB allocation, under constraints posed by the installed bandwidth in the transmission links of the network. The PB allocation procedure is driven from a traffic demand matrix and consists of three phases. In the first phase, a suitable decomposition of the whole network takes place, where the large-scale network is split to a set of one-level sub-networks. In the second phase, the optimization algorithm developed for one-level telecommunication networks is applied to each sub-network in order to define the optimal PB allocation. The criterion for optimization is to minimize the worst Call Blocking Probability (CBP) of all switching pairs of the sub-network. In the third phase, composition of the sub-networks takes place in a successive way, which leads to the final PB allocation of the large-scale network. As the large-scale network is built up from optimized sub-networks, an almost optimal PB allocation is anticipated. For evaluation, the worst resultant CBP of the proposed scheme is compared with that obtained by the optimal PB allocation procedure in order to prove its optimality and efficiency. We choose a set of large-scale networks whose size is not very large so that we can apply the optimization algorithm developed for one-level telecom networks for defining its optimal bandwidth allocation. Extensive evaluation of the PBM model has showed that the worst resultant CBP is about 2% above the optimal value, which is a satisfactory result. The proposed PBM scheme is explained by means of an application example.

Shared memory multiprocessors are frequently used as compute servers with multiple parallel programs executing at the same time. In such environments, an operating system switches the contexts of multiple processes. When the operating system switches contexts, in addition to the cost of saving the context of the process being swapped out and that of bringing in the context of the new process to be run, the cache performance of processors also can be affected. The blocked algorithm improves cache performance by increasing the locality of memory references. In a blocked program using this algorithm, program performance can be significantly affected by the reuse of a block loaded into a cache memory. If frequent context switching replaces the block before it is completely reused, the cache locality in a blocked program cannot be successfully exploited. To address this problem, we propose a preemption-safe policy to utilize the cache locality of blocked programs in a multiprogrammed system. The proposed policy delays context switching until a block is fully reused within a program, but also compensates for the monopolized processor time on processor scheduling mechanisms. Our simulation results show that in a situation where blocked programs are run on multiprogrammed shared-memory multiprocessors, the proposed policy improves the performance of these programs due to a decrease in cache misses. In such situations, it also has a beneficial impact on the overall system performance due to the enhanced processor utilization.

A variety of mobile data communication services based on cellular phones and the PHS (Personal Handyphone System) have recently been developed and used widely. The maximum transmission rate in public mobile data communication services is currently limited to 64 kbit/s, but higher transmission rate will be needed in order to meet the requirements of mobile multimedia applications. We have therefore developed 384 kbit/s-PHS experimental system that uses the 64 kbit/s PHS data communication protocol (PIAFS) and the PPP Multilink protocol. This paper presents the implementation and performance evaluation of the 384 kbit/s-PHS experimental system. Throughtput performance of the system is evaluated using FTP under various radio propagation environments.

When a mobile station with a call in progress moves across cell boundary in a cellular mobile communications system, the system must switch the circuit to the base station in the destination cell to enable uninterrupted communications in a process called "handoff. " However, if a circuit to the destination base station cannot be secured when a handoff is attempted, the call is forcibly terminated. Studies have therefore been performed on methods of decreasing the percentage of forcibly terminated calls by giving handoff calls priority. With the aim of simplifying system design, we propose a system for automatically setting the number of circuits reserved for handoff based on the handoff block rate. In this paper, we describe this system and evaluate static traffic characteristics taking into account reattempt calls, the occurrence of which can have a major effect on system performance. We also consider the effects of the proposed system on service quality since giving priority to handoff calls and decreasing the rate of forced terminations results in a tradeoff with the blocking rate of new call attempts. Finally, we evaluate the traffic characteristics associated with the number of control requests, an important element in estimating the processing capacity required by control equipment at the time of system design.

Recent development of compact and powerful portable computers and mobile phones and proliferation of the Internet will enable mobile multimedia communications. From the viewpoint of implementing multimedia services into mobile communications, it allows us to predict that traffic characteristics of mobile networks change. For planning, designing, and operating mobile multimedia networks, it is important to investigate traffic models which take the effect of multimedia services into consideration. This paper investigates population of active users in a micro-cell and proposes a traffic model for mobile multimedia networks. This model describes a population process of active users in a micro-cell in diffusion model, and its characteristics include self-similarity and activity of mobility. We also made an evaluation of network performance by using simulation, in order to show that characteristics of the proposed traffic model have impact on planning and designing networks.

We gave in [1] the software and hardware algorithms for reconfiguring 1 1/2-track switch 2-D mesh arrays with faults of processing elements, avoiding them. This paper shows an implementation of the hardware algorithm using an FPGA device, and by the logical simulation confirms the correctness of the behavior and evaluates reconfiguration time. From the result it is found that a self-repairable system is realizable and the system is useful for the run-time as well as fabrication-time reconfiguration because it requires no host computer to execute the reconfiguration algorithm and the reconfiguration time is very short.

To implement soft handoff in cellular communication systems that employ code division multiple access (CDMA), it is necessary to establish communication lines between the switch and multiple base stations and distribute the communication data via these multi-connections to the base stations simultaneously. This means that, when soft handoff is performed with the same amount of communication line resources as hard handoff, the blocking probability is higher than for hard handoff, and service quality is thus worse. Furthermore, handoffs occur more frequently as the size of cells becomes smaller, and this increases the probability of forced terminations. Switches must be endowed with greater processing capacity to accommodate the more frequent handoffs. The use of the queuing handoff method can be expected, in general, to mitigate forced termination probability compared with the immediate handoff method. In this regard, we propose a prioritized queuing handoff method that gives priority to fast-moving mobile stations (MSs) as a way to mitigate forced terminations even more than the non-priority queuing method without appreciably increasing the processing load. We then compare the traffic characteristics of our proposed method with these of three other methods in micro cell systems--immediate method, non-priority queuing method, and conventional hard handoff method without multi-connections--by computer simulation. Here, considering that the proposed method gives priority to fast-moving calls, traffic characteristics for these methods were evaluated separately for slow- and fast-moving MSs. The results reveal that proposed method can reduce the forced termination probability and total call failure probability more than non-priority queuing method without having an appreciable impact on slow-moving calls.

The essence of this work is to introduce an interaction between the physical layer and higher network layers, thus enabling a more practical utilization of multiuser detection and supporting services with different QoS parameters. In this paper, a new hybrid TDMA/ Multicode (MC)-CDMA medium access control utilizing multiuser detection is proposed and analyzed. Further, two traffic flow control approaches accompanied the TDMA/MC-CDMA system are proposed. One approach deterministically controls the flow of traffic into the TDMA slots, while the other statistically controls the flow of traffic depending on the instantaneous changes in the traffic load. The two approaches have been examined under a wide range of traffic characteristics where AWGN is only considered besides the mutual interferers from other intracell users. Both approaches show superiority as well as less sensitivity in terms of BER to the traffic changes compared with the conventional system.

A newly developed hybrid-integrated Symmetric Mach-Zehnder (HI-SMZ) all-optical switch is reported. For integration, we chose the Symmetric Mach-Zehnder (SMZ) structure rather than the Polarization-Discriminating Symmetric Mach-Zehnder (PD-SMZ) structure which is similar to SMZ but more often used in experiments using discrete optical components. We discuss advantages and disadvantages of SMZ and PD-SMZ to show that SMZ is more suitable for integration. We also discuss about the use of SOAs as nonlinear elements for all-optical switches. We conclude that, although the ultrafast switching capability of SMZ is limited by the gain compression of SOAs, the very low switching energy is more important for practical devices. We then describe the HI-SMZ all-optical switch. This integration scheme has advantages which include low loss, low dispersion silica waveguides for high speed operation and ease in large scale integration of many SMZs with other optical, electrical, and opto-electrical devices. We show that a very high dynamic extinction ratio is possible with HI-SMZ. We also examine HI-SMZ with 1 ps pulses to show its ultrafast capability. Finally, we describe a 168 to 10.5 Gbps error-free demultiplexing experiment which is to our best knowledge the fastest experiment with an integrated device.

A large-scale primarily public system requires in addition to high reliability, a broad range of applications from control to information services. As construction is phased-in this system must be flexible, changeable and able to grows as the needs arise. However, a changing a system may lead to loss of reliability. A system that is able to change and grow in a reliable and stable manner is called an assurance system and the technology it uses is called assurance technology. This paper describes the basic technology, phased-in system construction and so on of assurance technology based on an autonomous decentralized system. It further discusses application of assurance technology to ATOS as an example of a large-scale transport operation control system. Note: ATOS; Autonomous Decentralized Transport Operation Control System

The present paper modifies the algorithm to estimate harmful event frequencies and examines the definition of modes of operation in IEC 61508. As far as the continuous mode concerns, the calculated results coincide with those obtained based on the standard. However, for the intermediate region of medium demand frequencies and/or medium demand durations, the standard gives much higher harmful event frequencies than the real values. In order to avoid this difficulty, a new definition of modes of operation and a shortcut method for allocation of SILs are presented.

Hash routing is an algorithm for a distributed WWW caching system that achieves a high hit rate by preventing overlaps of objects between caches. However, one of the drawbacks of hash routing is its lack of robustness against failure. Because WWW becomes a vital service on the Internet, the capabilities of fault tolerance of systems that provide the WWW service come to be important. In this paper, we propose a duplicated hash routing algorithm, an extension of hash routing. Our algorithm introduces minimum redundancy to keep system performance when some caching nodes are crashed. In addition, we optionally allow each node to cache objects requested by its local clients (local caching), which may waste cache capacity of the system but it can cut down the network traffic between caching nodes. We evaluate various aspects of the system performance such as hit rates, error rates and network traffic by simulations and compare them with those of other algorithms. The results show that our algorithm achieves both high fault tolerance and high performance with low system overhead.

A rapid growth of the Internet and proliferation of new multimedia applications lead to demands of high speed and broadband network technologies. Routers are also necessary to follow up the growth of link bandwidths. From this reason, there have been many researches on high speed routers having switching capabilities. To have an expected effect, however, a control parameters set based on traffic characteristics are necessary. In this paper, we analyze the network traffic using the network traffic monitor and investigate the Internet traffic characteristics through a statistical analysis. We next show the application of our analytical results to parameter settings of high speed switching routers. Simulation results show that our approach makes highly utilized VC space and high performance in packet processing delay. We also show the effect of flow aggregation on MPLS. From our results, the flow aggregation has a great impact on the performance of MPLS.

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.

A systematic continuous data placement scheme on distributed multi-zone disks is developed for video on demand. The proposed scheme makes use of constant read time concept, i. e. , each video stream has the same access time in each service round when serving the request. The developed scheme maximizes not only the averaged data transmitted rate, but also the number of simultaneous accesses. The scheme consists of the following components. First we developed an algorithm that reorganizes the multi-zone disk into several logical zones in the sense that the averaged disk throughput is maximum. Second, a sequential data access method was developed that takes disk loading balance into account. Thus, at each service round, the total amount of data transmitted is a constant. Third, we introduce the idle round technique to reduce the buffer size required at the client site for VBR video stream. As a result, admission control is enforced in an efficient manner. Finally we perform experimental tests to evaluate the performance of the proposed scheme. The results indicate the value of the proposed scheme.