A performance model of partial packet discard and early packet discard schemes in ATM switches
In this paper, we develop a concise performance model of partial packet discard (PPD) and early packet discard (EPD) schemes in ATM switches. We study the performance of PPD and EPD with heterogeneous traffic sources. The sources included Poisson, and ON-OFF with long-tailed sojourn time distribution, which is approximated by a hyperexponential distribution. The fairness of EPD is investigated. We automatically generate and numerically solve the underlying Markov chain using a high-level graphical paradigm known as the stochastic reward net. Our numerical results reveal that: (1) the benefit of PPD and EPD is not significant when the queuing system is underloaded with Poisson sources; (2) PPD and EPD can increase the goodput when the system is overloaded or loaded with ON-OFF sources; (3) in All Poisson case, PPD and EPD provide nearly fair service to the sources; (4) the ON-OFF source gets higher goodput than the Poisson source. Because the burstiness of a source will be alleviated by the statistical multiplexing of ATM switches, the ON-OFF source may be viewed as the source that just enters the network, and the Poisson source may be viewed as the source being far away from the network node we are considering and has been regulated and smoothed by the switches it traversed. Therefore, the queuing system with EPD algorithm gives a higher goodput to the sources near it. And the sources far away from the system will have lower goodput. One of our principal conclusions is that per-VC-based scheme is not needed at the core of large ATM networks because the traffic is less bursty at the core of the networks and PPD and EPD are fair under this kind of environment. A per-VC-based scheme may be used at the edge of the ATM cloud. Such a configuration can make the core of the ATM network work at high speed. (C) 2001 Elsevier Science B.V. All rights reserved.
early packet discard atm stochastic reward net stochastic petri net package