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Yannis Smaragdakis
College of Computing
Georgia Institute of Technology
Atlanta, Georgia 30332
yannis@cc.gatech.edu
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Paul Wilson
Department of Computer Sciences
The University of Texas
Austin, Texas 78712
wilson@cs.utexas.edu
We examine a policy for managing modem pools that disconnects users only if not enough modems are available for other users to connect. Managing the modem pool then becomes a replacement problem, similar to buffer cache management (e.g., in virtual memory systems). When a new connection request is received, the system needs to find a user to ``replace''. In this paper we examine such demand-disconnect schemes using extensive activity data from actual ISPs. We discuss various replacement policies and propose CIRG: a novel replacement algorithm that is well suited for modem pools. In general, the choice of algorithm is significant. A naive algorithm (e.g., one that randomly replaces any user who has been inactive for a while) incurs many tens of percent more ``faults'' (i.e., disconnections of users who are likely to want to be active again soon) than the LRU algorithm, which, in turn, incurs 10% more faults than CIRG. For good replacement algorithms, the impact can be significant in terms of resource requirements. We show that the same standards of service as a system that does not disconnect idle users can be achieved with up to 13% fewer modems.
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This paper was originally published in the
Proceedings of the 2000 USENIX Annual Technical Conference,
June 18-23, 2000, San Diego, California, USA
Last changed: 24 May 2000 mc |
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Technical Program