Priority queue schedulers with approximate sorting in output-buffered switches
Liebeherr, J.
Wrege, D.E.
Dept. of Comput. Sci., Virginia Univ., Charlottesville, VA, USA;
This paper appears in: Selected Areas in Communications, IEEE Journal on Publication Date: June 1999
Volume: 17
,
Issue: 6
On page(s):
1127
- 1144
ISSN: 0733-8716
Digital Object Identifier: 10.1109/49.772446
Current Version Published: 2002-08-06
Abstract
All recently proposed packet-scheduling algorithms for output-buffered switches that support quality-of-service (QoS) transmit packets in some priority order, e.g., according to deadlines, virtual finishing times, eligibility times, or other time stamps that are associated with a packet. Since maintaining a sorted priority queue introduces significant overhead, much emphasis on QoS scheduler design is put on methods to simplify the task of maintaining a priority queue. In this paper, we consider an approach that attempts to approximate a sorted priority queue at an output-buffered switch. The goal is to trade off less accurate sorting for lower computational overhead. Specifically, this paper presents a scheduler that approximates the sorted queue of an earliest-deadline-first (EDF) scheduler. The approximate scheduler is implemented using a set of prioritized first-in/first-out (FIFO) queues that are periodically relabeled. The scheduler can be efficiently implemented with a fixed number of pointer manipulations, thus enabling an implementation in hardware. Necessary and sufficient conditions for the worst-case delays of the scheduler with approximate sorting are presented. Numerical examples, including traces based on MPEG video, demonstrate that in realistic scenarios, scheduling with approximate sorting is a viable option
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