Buffer overflow management in QoS switches

Abstract

Abstract. We consider two types of buffering policies that are used in network switches supporting Quality of Service (QoS). In the FIFO type, packets must be transmitted in the order in which they arrive; the constraint in this case is the limited buffer space. In the bounded-delay type, each packet has a maximum delay time by which it must be transmitted, or otherwise it is lost. We study the case of overloads resulting in packet loss. In our model, each packet has an intrinsic value, and the goal is to maximize the total value of transmitted packets.Our main contribution is a thorough investigation of some natural greedy algorithms in various models. For the FIFO model we prove tight bounds on the competitive ratio of the greedy algorithm that discards packets with the lowest value when an overflow occurs. We also prove that the greedy algorithm that drops the earliest packets among all low-value packets is the best greedy algorithm. This algorithm can be as much as 1.5 times better than the tail-drop greedy policy, which drops the latest lowest-value packets.In the bounded-delay model we show that the competitive ratio of any on-line algorithm for a uniform bounded-delay buffer is bounded away from 1, independent of the delay size. We analyze the greedy algorithm in the general case and in three special cases: delay bound 2, link bandwidth 1, and only two possible packet values.Finally, we consider the off-line scenario. We give efficient optimal algorithms and study the relation between the bounded-delay and FIFO models in this case.

Prompt Mechanisms for Online Auctions

“…Using the above characterization, it is possible to prove that the greedy algorithm is monotone [7] (see Section 2.4 for a description). Together with the result of [8], this gives a truthful mechanism that is 1 2 competitive. However, a closer look at this mechanism may make one wonder if it is indeed applicable.…”

“…Prompt mechanisms are very intuitive to the bidders as they (implicitly) correspond to takeit-or-leave-it offers: a winning bidder is offered a price for one item exactly once before getting the item, and may reject the offer if it is not beneficial for him. We improve upon the greedy algorithm of [7,8] by showing a different mechanism that achieves the same competitive ratio, but is also prompt.…”

“…The tardiness in the above mechanism [7,8] is substantial: there are inputs for which a bidder learns his payment only when he departs. Tardy mechanisms seem very unintuitive for the bidders, and in addition they suffer from the following disadvantages:…”

“…In the non-strategic setting, this problem and its variants have been widely studied (e.g., [1,8,3]). The best deterministic algorithm to date guarantees a competitive ratio of ≈ 0.547 [4,11], while it is known that no deterministic algorithm can obtain a ratio better than 2 √ 5+1 ≈ 0.618 [2].…”

Comparison-Based FIFO Buffer Management in QoS Switches

“…Kesselman et al [13] present the following simple greedy algorithm: Accept any arriving packet as long as the queue is not full. If a packet arrives while the queue is full, drop the packet with the smallest value.…”