Packet mode and QoS algorithms for buffered crossbar switches with FIFO queuing

Abstract

The buffered crossbar switch architecture has recently gained considerable research attention. In such a switch, besides normal input and output queues, a small buffer is associated with each crosspoint. Due to the introduction of crossbar buffers, output and input dependency is eliminated, and the scheduling process is greatly simplified. We analyze the performance of switch policies by means of competitive analysis, where a uniform guarantee is provided for all traffic patterns. We assume that each packet has an intrinsic value designating its priority and the goal of the switch policy is to maximize the weighted throughput of the switch. We consider FIFO queueing buffering policies, which are deployed by the majority of today's Internet routers. In packet-mode scheduling, a packet is divided into a number of unit length cells and the scheduling policy is constrained to schedule all the cells contiguously, which removes reassembly overhead and improves Quality-of-Service. For the case of variable length packets with uniform value density (Best Effort model), where the packet value is proportional to its size, we present a packet-mode greedy switch policy that is 7-competitive. For the case of unit size packets with variable values (Differentiated Services model), we propose a A preliminary version of this paper appeared in [23].β-preemptive (β is a preemption factor) greedy switch policy that achieves a competitive ratio of 6 + 4β + β 2 + 3/(β − 1). In particular, its competitive ratio is at most 19.95 for the preemption factor of β = 1.67. As far as we know, this is the first constant-competitive FIFO policy for this architecture in the case of variable value packets. In addition, we evaluate performance of β-preemptive greedy switch policy by simulations and show that it outperforms other natural switch policies. The presented policies are simple and thus can be efficiently implemented at high speeds. Moreover, our results hold for any value of the internal switch fabric speedup.

Improved Competitive Performance Bounds for CIOQ Switches

“…Kesselman and Rosén [22] considered the case of CIOQ switches with Priority Queuing (PQ) buffers and proposed a policy that is 6-competitive for any speedup. Kesselman et al [17,18] studied buffered crossbar switches with FIFO and PQ buffers.…”

Tight analysis of priority queuing for egress traffic

“…Moreover, Albers and Jacobs [3] performed an experimental study for the first time on several online scheduling algorithms for this model. Also, the overall performance of several switches, such as shared-memory switches [23,26,33], CIOQ switches [28,10,32,29], and crossbar switches [30,31], are extensively studied.…”

A survey of buffer management policies for packet switches

“…They propose a 4-competitive policy for the case of unit-sized, unit-valued packets with FIFO buffers, and an 18-competitive policy for general-valued packets but with Priority Queuing [KKS08a]. For the FIFO case, they also present a nonpreemptive 7-competitive switch policy for the case of variable-length packets that have uniform value density (that is, a packet's value is proportional to its size), and a preemptive 21-competitive policy for unit-sized packets with general values [KKS08c]. These bounds hold for arbitrary speedup.…”