This paper examines the requirements for creating a local safe map, which is the core of regional disaster prevention, through a case study in a historical local city in Japan. Amid the rising awareness of disaster prevention, efforts are being made in various places to voluntarily create disaster prevention maps through town walks. It is expected to improve residents' awareness of disaster prevention, improve local disaster prevention capabilities, and revitalize local communities. What are the requirements for a local safety map creation to continue to play a central role in regional disaster prevention rather than being a temporary event? Based on our past experiences, we review our research activity what is necessary to make such map-making the core of regional disaster prevention. The following is findings through our experience in the map-making activities. Sustainable development is possible by making it a regular activity in the district rather than a one-off event. Sharing of subjective information in cooperation with the disaster prevention division leads to improve reliability of information by consensus with the members and revitalization of activities through workshops. it is also necessary to select media that provide information from the user's perspective.

This paper describes a practical evaluation of our ICT-based regional safety map for a historical local town. In this kind of towns, it is required to make daily potential dangers visible and share them as basic information for regional safety. Our system supports local residents to post dangerous points in their living areas and share. We created and revised a local safety map under the cooperation of voluntary disaster prevention members. From the observation of the workshop and questionnaire survey, we found that (1) our system contributes to collect and share distinctive local danger information for the safety map, (2) the map provided by our system leads to awareness of safety by reaffirming nearby danger, and (3) the map is also useful for reviewing danger information and improving reliability through meeting.

Various kinds of high-quality media systems have been developed. It is expected that these systems can be used for remote lectures. We are adopting these systems including a high-speed network to construct a remote lecture based on "Instruction with Blackboard", which provides an old-fashioned but very common style of lecture. This instruction style has been often avoided in remote lectures so far because it requires high-quality data transmission. However it is no doubt that this style of instruction is still a very popular teaching method. Therefore, it is educationally meaningful that this teaching method is realized on remote lectures. This paper describes a construction method of the remote lecture based on Instruction with Blackboard and the experiment on the remote lecture using high-quality media systems.

The performances of the go-back-N ARQ scheme with selective repeat in intra-block (GBN-SR) and revised GBN-SR (Rev-GBN-SR) schemes are analyzed. Using the derived generating function of the service time of a packet, the throughputs of the proposed schemes are compared with that of Benelli's (1986) scheme. It is shown that the proposed Rev-GBN-SR scheme shows good performance in a wider range from low to high packet error rate regions.

In this paper, we determine an exact formula for the throughput performance of the GBN SR scheme, in which the go-back-N ARQ scheme is used for inter-block transmission and the selective repeat scheme is used for intra-block transmission. Using that formula, the throughput performance of GBN SR scheme is compared with that of Benelli's (1986, 1993) scheme in a numerical manner. As a result, it is shown that the throughput performance of the GBN SR scheme is superior to that of Benelli's scheme in a wider range of packet error rate from low to medium, but is inferior at high packet error rates.

The DQDB MAC Protocol standardized by the IEEE 802.6 Committee is the single segment bandwidth reservation scheme that reserves the bandwidth for only one segment in the distributed queue. Recently, the multi-segment bandwidth reservation schemes that reserve the bandwidth for not only one segment in the distributed queue but also a part of or all segments in the local node queue have been proposed. In this paper, we propose a new multi-segment bandwidth reservation protocol that can quickly react to changes of node's traffic and can quickly allocate bandwidth fairly and waste-free. We also evaluate the mean message transmission delay and the throughput convergence performance by simulation. As a result, the mean message transmission delay can be decreased and the throughput can be quickly converged to the fair bandwidth allocation.

The tandem-type go-back-N (GBN) scheme has been proposed for satellite communications to reduce the long roundtrip delay using the onboard processing of satellites. The author considers the exact analysis of the throughput performance of this scheme and its application to a broadcast communications system such as a point-to-multipoint file transfer system. First, the throughput expression for the point-to-point tandem-type GBN scheme is derived. Second, applying the results of this point-to-point tandem-type GBN scheme to a broadcast (point-to-multipoint) communications system, the relationship of the number of receiving stations to the link bit error rate and the roundtrip propagation delay is shown.>

The characteristics of the transmission delay packets in continuous ARQ (automatic-repeat-request) system, a class of the go-back-N system, are considered. In this ARQ scheme the multiple copies of each packet stored in a buffer, instead of one packet itself, are transmitted to reduce the delay. The generating function of the delay and its average is derived. It is shown that the optimum copy-size minimizing the average delay is given not only by the propagation delay and the packet error rate but also by the traffic intensity.>