This paper presents a newly developed analytical method which evaluates the virtual path bandwidth control effects for a general topology ATM (Asynchronous Transfer Mode) transport network. The virtual path concept can enhance the controllability of path bandwidth. Required link capacity to attain a specified call blocking probability can be reduced by applying virtual path bandwidth control. This paper proposes an analytical method to evaluate the call blocking probability of a general topology ATM network, which includes many virtual paths, that is using virtual path bandwidth control. A method for the designing link capacities of the network is also proposed. These methods make it possible to design an optimum transport network with path bandwidth control. Finally, a newly developed approximation technique is used to develop some analytical results on the effects of dynamic path bandwidth control are provided to demonstrate its effectiveness.

This paper proposes two algorithms for defining a routing domain in multiclass-of-service networks. One an off-line-based method, whose objective is to optimize dynamic routing performance by using precise knowledge on the traffic levels. The algorithm of the proposed method takes into account the random nature of the traffic flow, which is not considered in the network flow approach. The proposed method inherits the conceptual simplicity of the network flow approach and remains applicable to large and complex networks. In simulation experiments, the proposed off-line-based method performs better than the method based on the network flow approach, but has a similar the computation time requirement. The other method proposed here is an on-line-based method for application to B-ISDNs, where precise traffic data is not expected to be available. In this method, the routing domain is defined adaptively according to the network performance (call-blocking probability) measured in real-time. In simulation experiments, the performance of this method is comparable to that of the off-line-based method--especially when highly efficient dynamic routing is used. This paper also derives and describes methods for approximating the implied costs for multiclass-of-service networks. The approximations are very useful not only for off-line-based routing domain definition (RDD) methods but also for other kinds of network controls or optimal network dimensioning based on the concept of revenue optimization.

This paper describes a fully digitized modem designed for variable baud rate transmission systems with the aim of efficiently providing multimedia services over a wireless communication network. The concept of a variable baud rate wireless communication system is discussed focusing on the access scheme and channel allocation from the viewpoint of frequency utilization efficiency. For easy system construction, we propose a fully digitized variable baud rate modem based on multirate digital signal processing, taking into account the need for even performance and easy clock control for all transmission rates. We also discuss the operational principle of modulation, the degradation factor in the A/D converter, and the configuration of the clock recovery circuit. Steady modulation performance can be kept by generating the same frequency system clock for all transmission rates and using the sampling rate conversion technique without selecting the channel filter for each transmission rate. It is proved by the analysis of the degradation factor in the A/D converter that only the bandwidth of the channel filter in demodulator should be changed for the transmission rate. A double loop clock recovery configuration capable of both tank-limit type and baseband estimation type clock recovery is shown to be suitable for this system. The tank-limit clock recovery circuits can be constructed easily by employing a tank circuit array. Finally, we present experimental results for a modem having transmission rates of 1.544Mbps and 6.312Mbps for the digital hierarchy and information speed of video signals such as MPEG-1 and MPEG-2. The measured basic performance of the proposed modem shows it delivers superior performance without the need for precise adjustment when a QPSK modulation scheme is employed.

Calls using different media which require different transfer quality will arrive at ATM networks. Therefore it is important to develop a method for allocating network resources efficiently to individual calls by judging admission of calls. Various call admission control schemes have been already proposed, and these schemes assume that users specify values of traffic descriptors when they originate calls. However, it is sometimes difficult for users to specify these values accurately. This paper proposes a new ATM call admission control scheme based on cell transfer state monitoring which does not require that users specify values of traffic descriptors in detail when they originate calls. In this proposed scheme, the acceptance or rejection of calls is judged by comparing the monitored cell transfer state value with a threshold prepared in advance. This threshold must be adjusted according to changes in the characteristics of traffic applied to ATM networks. This is one of the most serious problems in the control scheme based on the monitoring of cell transfer state. Herein, this paper proposes neural network application to the control scheme in order to resolve this problem and improve performance. In principle, the threshold can be adjusted automatically by the self-learning function of the neural network, and the control can be maintained appropriately even if the characteristics of traffic applied to ATM networks change drastically. In this paper, the effectiveness of the application of a neural network is clarified by showing the configuration of this proposed control scheme with the neural network, a method for deciding various parameter values needed to implement this control scheme, and finally the results of a performance evaluation of the control scheme. Inputs required by the neural network are also discussed.

The recent progress of B-ISDN signaling systems has enabled networks to handle calls which require a wide variety of ATM connection sets. This paper is concerned with the circuit group which handles calls requesting asymmetric forward and backward multi-connections, and has the capability of both bandwidth negotiation and bandwidth reservation as a traffic control for enhancing call blocking performance. A model of the circuit group is first established focusing on the call level characteristics of the group, and then a method based on the reduced load approximation and an approximate analysis of a multirate group is proposed for calculating approximate blocking probabilities. The accuracy of the approximation method is evaluated numerically by comparing with an exact method and simulation. Further the impact of bandwidth negotiation and reservation on call blockings is examined based on numerical examples.

This paper proposes a hybrid access control scheme for broadcast-based ATM-LANs. Broadcast-based ATM-LANs are shared media networks with star topology. In this network, packets are broadcast to all subscriber terminals by a CPYF (Cell COPY Function) node located in the ATM network and only relevant packets are extracted and sent to the destined user layer function by packet filtering functions in the terminals. The simplicity of the packet transfer mechanism makes the network very economical. In broadcast-based ATM-LANs, the hybrid access control scheme is effective in improving performance. In this scheme, short packets and long packets are transmitted respectively by means of a back-pressure type and a CSMA/CD type access control scheme. Throughput evaluation was performed by computer simulation and the results show that the proposed scheme achieves a high throughput characteristic.

We investigated performance of routing schemes in B-ISDN, for heterogeneous traffic flows under various bandwidths. In particular, we compared the simulated performance of these schemes by evaluating their blocking probabilities. To achieve high performance, these schemes use special kinds of routing algorithm, one which is pre-selection algorithm and one which is cyclic algorithm. We investigated the efficiency of the pre-selection algorithm and the robustness of the cyclic algorithm for nonuniform traffic and network resources. We found that these routing algorithm schemes can compensate for errors in resource design.

A uniquely-structured Usage Parameter Control (UPC) method named Virtual-shaping is proposed which considers cell arrival time jitter between user and UPC point. The method uses a modified Dangerous Bridge UPC circuit (Sliding window type) and virtually (logically) shapes cell traffic using cell arrival time compensation to offset cell delay variation (CDV). In addition, the proposed method is based on a cell-buffer-less structure and can be realized with reasonable hardware. The method yields precise and accurate monitoring. Computer simulations show that the method offers higher network utilization than the conventional Leaky Bucket based UPC method. The proposed method will make it possible to create more effective B-ISDNs, and more cost-effective broadband VBR services.

This paper examines performance study items for ATM connections in B-ISDNs. We consider the characteristics of B-ISDN performance and describe the current status in ITU-T and the ATM Forum. On this basis, we propose a new performance framework and performance criteria. We also describe objectives for ATM cell transfer performance.

This paper deals with network performance of 64kbit/s-based services supported in an ATM network and an ATM interworking network with 64kbit/s-based networks. It first clarifies network performance issues giving a model and objectives of study and experiment. A result of computational analysis is then presented, where a cell loss ratio of an order of 10-4 or 10-5 is obtained to give a performance equivalent to that currently used as objective values in existing networks for a 64kbit/s digital level. In order to capture the impact of cell loss and associated performance for application levels, an experimental test has been carried out using typical applications. Test results show that the cell loss ratio needs to be approximately ten times better than the bit error ratio for comparable performance for application levels. A cell loss ratio of better than 10-5, or an order of 10-6 considering an interworking situation, seems to be necessary according to the test results. It is further clarified by the test that a single cell is more valuable than a multiplexed cell for providing better cell loss resilience characteristics. Although not all applications of 64kbit/s networks have been tested, it is expected that the test results can be used as guidance for considering the support of 64 kbit/s services in an ATM and interworking networks.

Recently as one of attractive applications in the B-ISDN era, LAN/MAN interconnection through an ATM network has been coming up because burstiness of LAN/MAN data traffic is applicable to distinctive features of cell based ATM network. In order to overcome a difference of the connection mode, i.e., CL packet transfer of LAN/MAN and CO cell transfer of ATM network, a number of interworking and bandwidth allocation mechanisms have been proposed. These methods, however, indicate both merits and drawbacks concerning with CL data transfer quality, network resource efficiency and processing overhead in IWU/CLS and the network, and have been mostly evaluated only for a single IWU model. This paper aims at showing the most appropriate method of LAN/MAN interworking for IWU-IWU or IWU-CLSF connection. In the paper, some interworking issues including a general qualitative assessment are clarified. We then evaluate the selected five interworking methods based on Bandwidth Renegotiation (BR) and VC Establishment (VCE), which are combined with Traffic Enforcement Functions (TEFs) based on policing mechanisms and Cell Loss Control (CLC) scheme. By transient and stationary simulation approach for a single IWU and an IWU-CLS connection model, the most applicable method is indicated as a case study from view points of the communication quality, effective use of the bandwidth and processing load.

In current teleteaching systems, video conferencing systems have been used to transmit a motion video from a teacher's site. A video that captures a teacher or his or her chalkboard is transmitted to a remote site through a communication channel. Since the resolution of the video is not very high, a camera captures either a teacher or a chalkboard, but not both at the same time. Thus, remote students have difficulty in obtaining realistic sensation. Another approach to realizing teleteaching is to use a computer-based desktop conferencing system that supports a motion video and a computer-based shared chalkboard. In this approach, a teacher has to use a mouse or a handwriting tablet for input, and therefore cannot use a real chalkboard. Moreover, the teacher cannot use gestures to remote students. This paper presents a multimedia teleteaching system that integrates an electronic whiteboard with a multimedia desktop conferencing system for providing realistic sensation to remote students. The system provides two-way communication of a video and a computerized chalkboard. A teacher uses an electronic whiteboard as a real whiteboard using direct manipulation, and transmits his or her gestures to remote students by using video communication. The system provides dual views; one view is for teacher's gestures and the other is for chalkboard contents. By providing the dual views, the system can transmit teacher's gestures all the time. Since chalkboard contents are processed and displayed as computer data, students can see them clearly. With the computerized chalkboard, a teacher or a student can zoom contents, input data written on a paper using a scanner, or add annotation.

The new algorithm for VP bandwidth control described and analyzed in this paper is a revised version of the Successive Modification Method. Its operation is based only on call-level performance (call blocking probabilities) measured in real time, without explicitly taking the cell-level performance into account. This algorithm does not need to predict future traffic demand and to perform network-wide optimization according to the predicted traffic. These features are well suited for a B-ISDN environment, with the variety of ATM bearer services and the uncertainty of their traffic demand and other characteristics. This paper describes the relationship between the proposed control and other traffic controls in ATM networks, such as CAC and VP shaping/policing. It also offers a solution to the problem of the competition that arises when several VPs in the same transmission path need increased bandwidth. Evaluation of the transient behavior of the VP bandwidth occupied by VCs shows that there is a lower limit in the control cycle and that this limit can be estimated as the longest average holding time of VCs among all services. Numerical results obtained using a call-by-call simulator show that proposed control is effective in preventing the performance degradation caused by a large traffic imbalance in communications networks. Comparison of the proposed control with a dynamical alternate routing for VC reveals that the VP bandwidth control is effective in relieving only the areas showing serious performance degradation, but that it is not so effective in improving the overall network performance.

A high-efficiency air cooling system is one of the keys to achieving high throughput in an ATM switching system for Broadband ISDN. Our approach is to cool the multichip modules plugged into a planar packaging system by using a two-phase thermosyphon cold-plate with an air-cooled condenser. Physically separating the cold-plate and the air-cooled condenser and connecting item by small diameter pipes is the key to applying this cooling technology to large planar packaging systems to increase volumetric packaging densities. Furthermore, thermosyphon technology allows the heat transfer process to operate without any external pumping power. Therefore this cooling system is regarded an extended high-performance air cooling system. The optimum structure was investigated while focusing on ways to reduce the external thermal resistance. The external thermal resistance between the system's cold-plate and air inlet was measured to be 0.21 K/W at an air velocity of 2 m/s and a cooling duty of 150 watts. Using this external thermal resistance value, we simulated the cooling characteristics of an MCM containing a 44 array of 10-mm-square LSI chips on an alumina substrate measuring 100100 mm. For an allowable temperature rise of 60, simulated thermal resistance was 6 K/W at an air flow of 2 m/s. This allows a power dissipation of more than 160 watts per MCM and a heat flux of 1.6 W/cm2. This system will extend the applicability of air cooling to power levels generally considered to lie in the domain of liquid cooling, and thus to the ATM switching nodes for B-ISDN.

It is important for distributed computing environments that communication networks are transparent to applications. This allows applications to make the best use of computer resources, To realize network transparency, communication platforms which support distributed computing environments should have a system configuration like an extension of a workstation's internal bus. Such communication platforms require high-speed communication paths, ability to handle different transmission speeds, high reliability, and scalability. This paper proposes a broadband distributed data network which satisfies the above requirements, and provides a distributed computing environment. Our system uses basic nodes called ATM-HUBs and ATM-Gateways (ATM-GWs) as its central components. The nodes consist of cell switch modules which can be made up of building blocks, ATM interface modules, and other functional modules. The switch module is connected to functional modules through a unified interface. The ATM-HUB in particular has conventional LAN interface modules. Using the conventional LAN interface and ATM interface module in an ATM-HUB, a wide variety of terminals, including conventional LAN terminals and ATM terminals, can be accommodated, so offering flexibility of communication modes to users. Furthermore, the use of star wiring around the ATM-HUB and media access control (MAC) address routing gives a higher transfer rate comparable to the speed of a physical transmission line for communication between ATM terminals, or between conventional LAN terminals.

A local area network (LAN) can now provide high-speed data communications in a local area environment to establish distributed processing among personal computers and workstations, and the need for interconnecting LANs, which are geographically distributed, is naturally arising. Asynchronous Transfer Mode (ATM) technology has been widely recognized as a promising way to provide the high-speed wide area networks (WAN) for Broadband Integrated Services Digital Network (B-ISDN), and the commercial service offerings are expected in the near future. The ATM network seems to have a capability as a backbone network for interconnecting LANs, and the LAN interconnection is expected to be the first service in ATM networks. However, there remain some technical challenges for this purpose; one of the main difficulties in LAN interconnection is the support of connectionless traffic by the ATM network, which is basically a connection-oriented network. Another one is the way of achieving the very high-speed data transmission over the ATM network. In this paper, we first discuss a LAN internetworking methodology based on the current technology. Then, the recent deployments of LAN interconnection methods through B-ISDN are reviewed.

Connectionless service for LANs interconnection will be provided in ATM networks at an early stage of B-ISDN era. This service will be provided on connection oriented mode at ATM technology. To perform this service, ATM connections using the dedicated bandwidth for this service are established semi-permanently between the nodes accommodating LANs. On these ATM connections, connectionless service among LANs is provided. It is important for private networks to utilize this bandwidth efficiently for reducing communication cost. In this paper, the architecture to provide connectionless service in private networks is described. Next, the allocation schemes of the bandwidth for this service and their performance are considered. We discuss the following schemes and compare them. One scheme is to establish semi-permanent ATM connections between the nodes with LAN interfaces. The bandwidth for each connection is individually assigned between these nodes. In another scheme, CLSFs (Connection-Less Service Functions) are introduced for connectionless service and connections are established via CLSFs. We show the latter scheme is superior because it brings out the effectiveness of statistical multiplexing of ATM technology and it leads to the reduction of the allocated bandwidth.

This paper deals with methods for interconnection between two local private networks that are geographically separated. A scheme is first presented to chain low bit-rate physical circuits into one logical circuit, over which ATM cells are transmitted as if there is one circuit with a high bit-rate capacity. In particular, use of existing low bit-rate circuits, e.g., 384/1536 kbit/s PDH leased line services and N-ISDN switched channels, is considered. The paper discusses two methods to permit chaining of physical circuits, and identifies their advantages and applications. By using the ATM-based circuit-chaining method, dynamic capacity control of the interconnection is then introduced with the use of an ATM-based rate adaptation. This is intended to provide a flexible and cost-effective capacity control compared to the existing TDM-based control. It is also possible to realize non-stop operation of changing capacity by establishment and release of chained circuits, which will lead to high reliability and robustness of private networks. Finally, delay characteristics introduced by the method are evaluated based on a computer simulation which gives a short and acceptable delay.

There has been growing interest in Broadband ISDN (B-ISDN) based on ATM (Asynchronous Transfer Mode) technologies, since ATM is expected to support a wide range of applications through high-speed and flexible multimedia communication capabilities. This paper reviews and discusses technical issues on multimedia communication protocols and services from the integration points of view of computer and communication technologies. An ISDN-based distributed multimedia and multi-party desktop conference system called MERMAID is introduced as an example which offers highly-sophisticated functions for remote collaborations among multiple users. This system, which was developed in early 1989 and has been used for daily research work since then, involves B-ISDN key technologies related to multimedia and multicast protocols, and computer architecture for groupware applications.

The demand for large-capacity photonic switching systems will increase as regular broadband ISDN (B-ISDN) spreads and full-motion video terminals replace telephones. Large-scale and economical optical fiber transmission lines have been built based on time-division (TD) multiplexing. To reduce costs, it is important to increase the channel multiplexity of both transmission and switching systems by using TD and wavelength-division (WD) or frequency-division (FD) technologies. We surveyed photonic switching systems' architecture and switching network structures. Switching can be divided into circuit or synchronous transfer mode (STM) switching, and asynchronous transfer mode (ATM) switching. A variety of photonic STM and ATM switching systems based on the two switching technologies have recently been proposed and demonstrated.