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[Author] Toshihisa OZAWA(3hit)

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  • Performance Characteristics of a Packet-Based Leaky-Bucket Algorithm for ATM Networks

    Toshihisa OZAWA  

     
    LETTER-Communication Networks and Services

      Vol:
    E82-B No:1
      Page(s):
    184-187

    A packet-based leaky-bucket algorithm functions like the early packet discard (EPD), and accepts a newly arriving packet if the probability that all the cells of the packet are accepted is high. We derive some performance characteristics of the cell and packet arrival processes that are accepted by the leaky-bucket algorithm. From these analyses, a method to determine the values of the parameters of the leaky-bucket algorithm and certain relations between this leaky-bucket algorithm and the generic cell rate algorithm (GCRA) are obtained.

  • Method of Bandwidth Dimensioning and Management for Aggregated TCP Flows with Heterogeneous Access Links

    Ryoichi KAWAHARA  Keisuke ISHIBASHI  Tatsuya MORI  Toshihisa OZAWA  Takeo ABE  

     
    PAPER-Internet

      Vol:
    E88-B No:12
      Page(s):
    4605-4615

    We propose a method of dimensioning and managing the bandwidth of a link on which flows with heterogeneous access-link bandwidths are aggregated. We use a processor-sharing queue model to develop a formula approximating the mean TCP file-transfer time of flows on an access link in such a situation. This only requires the bandwidth of the access link carrying the flows on which we are focusing and the bandwidth and utilization of the aggregation link, each of which is easy to set or measure. We then extend the approximation to handle various factors affecting actual TCP behavior, such as the round-trip time and restrictions other than the access-link bandwidth and the congestion of the aggregation link. To do this, we define the virtual access-link bandwidth as the file-transfer speed of a flow when the utilization of the aggregation link is negligibly small. We apply the virtual access-link bandwidth in our approximation to estimate the TCP performance of a flow with increasing utilization of the aggregation link. This method of estimation is used as the basis for a method of dimensioning the bandwidth of a link such that the TCP performance is maintained, and for a method of managing the bandwidth by comparing the measured link utilization with an estimated threshold indicating degradation of the TCP performance. The accuracy of the estimates produced by our method is estimated through both computer simulation and actual measurement.

  • Approximate Distribution of Processor Utilization and Design of an Overload Detection Scheme for SPC Switching Systems

    Toshihisa OZAWA  

     
    PAPER

      Vol:
    E75-B No:12
      Page(s):
    1287-1291

    Processors are important resources of stored program control (SPC) switching systems, and estimation of their workload level is crucial to maintaining service quality. Processor utilization is measured as processor usage per unit time, and workload level is usually estimated from measurement of this utilization during a given interval. This paper provides an approximate distribution of processor utilization of SPC switching systems, and it provides a method for designing an overload detection scheme. This method minimizes the observation interval required to keep overload detection errors below specified values. This observation interval is obtained as an optimal solution of a linear programming.