Kazutomo Kobayashi

Steady-state analysis of ATM multiplexer with variable input rate through diffusion approximation

Abstract We propose an approximation formula for the stationary distribution of the buffer content Qt of a fluid model for an ATM multiplexer in which the input rate process Rt is given as a Gaussian process of the form Rt = m + ∝t−∞ h(t − s) dws, where ws is a standard Wiener process. To derive the approximation formula, we approximate the behavior of Qt by a diffusion process on R (−∞, ∞) having no reflecting barrier. Simulation results show that the formula provides good approximate values. The formula is similar to the one derived by H. Kobayashi and Q. Ren for multiple On-Off types of traffic, but probabilistically it seems more reasonable. Our model is fairly general and it covers almost all variable input rate processes proposed so far for ATM multiplexer. In this sense, the new approximation formula provides a useful tool to analyse and estimate the congestion in the buffer of the ATM multiplexer.

Configuration rule and performance evaluation for DiffServ parameters

The Internet is becoming an important communication infrastructure of the society, and thus it is no longer sufficient to simply be able to provide connections: a higher quality of service (QoS) in communications is increasingly being required. As a new framework for providing QoS services, DiffServ is undergoing a speedy standardization process at the IETF. DiffServ not only can offer tiered levels of services, but can also provide guaranteed QoS to a certain extent. In this paper, we examine a single DiffServ node model which utilizes a token bucket as the policing mechanism, and propose a way of configuring various control parameters in order to accommodate various UDP/TCP traffic. Then, through simulation, we evaluate the throughput characteristics in various cases where TCP and UDP are mixed or separated in different queues, and study the appropriateness of the configurations. The results indicate that the throughputs can be maintained as specified in the Service Level Agreements (SLA) over a considerably wide range of bucket sizes and discard thresholds in the QoS control mechanism.

Tail probability of a Gaussian fluid queue under finite measurement of input processes

Recently, there has been frequent discussion of whether communication traffic is long-range dependent or not. This paper gives another insight to this issue by discussing the problem of estimating the tail probability P(Q > x) of a Gaussian fluid queue under finite measurement of input processes.