SRED: stabilized RED

Abstract

This paper describes a mechanism we call "SRED" (stabilized random early drop). Like RED (random early detection) SRED pre-emptively discards packets with a load-dependent probability when a buffer in a router in the Internet or an intranet seems congested. SRED has an additional feature that over a wide range of load levels helps it stabilize its buffer occupation at a level independent of the number of active connections. SRED does this by estimating the number of active connections or flows. This estimate is obtained without collecting or analyzing state information on individual flows. The same mechanism can be used to identify flows that may be misbehaving, i.e. are taking more than their fair share of bandwidth. Since the mechanism is statistical in nature, the next step must be to collect state information of the candidates for "misbehaving", and to analyze that information. We show that candidate rows thus identified indeed have a high posterior probability of taking a larger than average amount of bandwidth.