SKEL: A fundamental property desirable in ATM switches for simple traffic management - illustrations with generic output-buffered and input-buffered switches

Abstract

To simplify traffic control in a network, it is desirable that the traffic-control policy at a network node depends only on the external traffic loads on the input and output links, but not on the detail addressing 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 possible 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 nonuniform traffic distribution from inputs to outputs is better than or close to the performance under the uniform traffic distribution. The contributions of this paper are twofold: clarifying issues related to SKEL and establishing its feasibility for generic input- and output-buffered switches on a rigorous basis. The following summarizes our major results: (1) The packet-loss probability due to the Knockout switch-design principle for packets destined for an arbitrary output is maximum when the traffic to that output originates uniformly from all inputs; (2) The packet-loss probability for packets destined for a particular output under uniform traffic closely approximates the loss probability for packets from the worst-case input to that output under nonuniform 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.