SKEL - A FUNDAMENTAL PROPERTY DESIRABLE IN ATM SWITCHES FOR SIMPLE TRAFFIC MANAGEMENT - ILLUSTRATIONS WITH GENERIC OUTPUT-BUFFERED AND INPUT-BUFFERED SWITCHES

To simplify traffic control in a network, it is desirable that the tra ffic-control policy at a network node depends only on the external tra ffic loads on the input and output links, but not on the detail addres sing or distribution of packets from inputs to outputs. In other words , it should be possible to guarantee the grade-of-service of an input- output connection by controlling the aggregate loads on the input and output. Switch nodes in which such a traffic-control policy is possibl e are said to have the property of the sufficiency of the knowledge of external loads (SKEL). One way to demonstrate the feasibility of SKEL for a particular switch is to show that the performance under any non uniform traffic distribution from inputs to outputs is better than or close to the performance under the uniform traffic distribution. The c ontributions of this paper are twofold: clarifying issues related to S KEL and establishing its feasibility for generic input- and output-buf fered switches on a rigorous basis. The following summarizes our major results: (1) The packet-loss probability due to the Knockout switch-d esign principle for packets destined for an arbitrary output is maximu m when the traffic to that output originates uniformly from all inputs ; (2) The packet-loss probability fur packets destined for a particula r output under uniform traffic closely approximates the loss probabili ty for packets from the worst-case input to that output under nonunifo rm traffic; (3) For mean and variance of delay, similar results as in (1) and (2) can be obtained; (4) For an input-queued switch, external link loadings that do not give rise to queue saturation under uniform traffic will not do so under nonuniform traffic either.