VLBI is an important application of ATM technology because it can transmit huge amounts of data. A single VLBI experiment typically generates data (which must be recorded and transported until they are cross-correlated) of tera-bit order at each separated observing site. Conventional VLBI not only requires manpower but also limits the maximum observation data rate. Therefore, a realtime VLBI using a private ATM network was developed recently, but it could not be utilized for regular VLBI experiment. Since utilization of public ATM is most realistic solution for realtime VLBI between ordinary observing sites, we have developed an interface equipment that connects VLBI observation and processing equipment to a public ATM network and demonstrated a successful experiment. This equipment supports VLBI's standard bit rates as 128 Mbps and 256 Mbps, though data rate for user's payload in 155.52 Mbps (STM-1/OC-3) ATM network is actually only 119.5 Mbps. It can easily step to higher networks as 622 Mbps.

The Communications Research Laboratory (CRL), the National Astronomical Observatory (NAO), the Institute of Space and Astronoutical Science (ISAS), and the Telecommunication Network Laboratory Group of Nippon Telegraph and Telephone Corporation (NTT) have developed a very-long-baseline-connected-interferometry array, maximum baseline-length was 208 km, using a high-speed asynchronous transfer mode (ATM) network with an AAL1 that corresponds to the constant bit-rate protocol. The very long baseline interferometry (VLBI) observed data is transmitted through a 2.488-Gbps [STM-16/OC-48] ATM network instead of being recorded onto magnetic tape. By combining antennas via a high-speed ATM network, a highly-sensitive virtual (radio) telescope system was realized. The system was composed of two real-time VLBI networks: the Key-Stone-Project (KSP) network of CRL (which is used for measuring crustal deformation in the Tokyo metropolitan area), and the OLIVE (optically linked VLBI experiment) network of NAO and ISAS which is used for astronomy (space-VLBI). These networks operated in cooperation with NTT. In order to realize a virtual telescope, the acquired VLBI data were corrected via the ATM networks and were synthesized using the VLBI technique. The cross-correlation processing and data observation were done simultaneously in this system and radio flares on the weak radio source (HR1099) were detected.

Asynchronous Transfer Mode (ATM) technology is expected to be used in constructing a B-ISDN. ATM networks must support a variety of services, e.g., voice, data, and image communications with different grade of service requirements. The demand for these services and their traffic characteristics, however, are not yet clear. To implement B-ISDN under this situation, it is necessary to establish a network control scheme that can' absorb the difference between the estimated traffic and the traffic that is actually offered. In ATM networks, virtual path bandwidth control is a key control scheme for absorbing this traffic estimation error, and several control algorithms have already been proposed. When we try to further utilize the VP resource by dynamically reallocating the bandwidth according to the short-term traffic variation, however, we need control schemes that are highly responsive. This is achieved by using control intervals that are shorter than the intervals over which traffic fluctuates. Control algorithms based on central controllers generally need to collect a large amount of information from geographically widespread network facilities and solve a large optimization problem. This can make them difficult to use with short control intervals in large networks. An alternative enabling the shorter control periods is to use multiple distributed controllers that use only local information. This paper proposes two new VP bandwidth control algorithms suitable for this distributed implementation. In these algorithms, decentralized controllers are located at network nodes including ATM switch (ATM-SW) or ATM cross connect (ATM-XC) function, and each controller observes the quality of the VPs relevant to it. The bandwidth is modified successively as these distributed controllers communicate with each other. We therefore call this method "successive modification method" (SMM). Numerical evaluation using a model network shows the effectiveness of these algorithms for preventing the performance degradation caused by large-scale traffic imbalance within a network. Comparison with the batch modification method (BMM), which has no feedback effect, shows that the proposed SMM with approprate control intervals can be more responsive to traffic variation over time, but is slightly inferior when network conditions are static.

We have developed a network architecture that achieves ATM multicast communication services with receiver-specified quality of service (QoS) guarantee which depends on the dynamic resource environment of the receivers (e.g. CPU capability, memory capability, and network capability). We propose two receiver-initiated QoS guarantee methods and concentrate on the functions required to achieve them. Moreover, on our ATM testbed, we also evaluate the performance of an experimental implementation of the proposed methods.

The Asynchronous Transfer Mode (ATM) is expected to be the basic transmission technology for B-ISDN. Before this happens, however, it will be necessary to predict the impact of fully-deployed ATM-based networks quantitatively. This paper compares the cost-efficiency of an ATM-based network with that of an STM-based network and clarifies the applicable areas of ATM network configurations, in terms of required facilities and considering the effect of statistical multiplexing. It shows cost-effective network configurations based on different service classes and a network configuration suited to ATM. It also discusses the effect of a Synchronous Digital Hierarchy architecture for Virtual Path dimensioning.

This paper presents a realization of our IP based realtime VLBI (Very Long Baseline Interferometer) observation testbed with the highest sensitivity in the world. Today's rapid deployment of high-speed wide area networks will give a major breakthrough in VLBI astronomy in terms of its observational sensitivity and immediateness. VLBI requires huge amount of data transfer from several radio telescopes located separately each other for calculating cross-correlation. High-speed networks can be applied to such data transfer instead of conventional magnetical tape recording and physical transportation, which cause a serious performance bottleneck. We have newly designed and implemented a special component named gigabit network access node, which can exchange 2.048 Gbps telescope data through a 2.488 Gbps OC-48c/STM-16c SONET/SDH link. We have also constructed the world's first multi-gigabit-rate VLBI observation testbed using actual high-speed wide area optical networks and successfully conducted several real observations.