We are grateful to the anonymous reviewers and our shepherd, Liviu Iftode, for their helpful comments. Thanks to Erich Nahum at IBM T.J. Watson for providing us with the www.ibm.com trace. This work was supported in part by NSF Grant CCR-9803673, by Texas TATP Grant 003604, by an IBM Partnership Award, and by equipment donations from Compaq Western Research Lab and HP Labs.