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From: Eric Hughes <hughes@ah.com> Date: Saturday, August 06, 1994 4:02PM
Hal's random-send spool has an expected value of latency which is approximately the size of the spool but has no deterministic upper bound for that latency. Fine. Great. No problem. There should be zero hesitation here, because the expected value -- the probabilistic average -- is what you want.
There is an important distinction between systems for which the only observable behavior is the probabilistic average and those for which the observable behavior is that of the individual actions. An example of the former system is a hash table with open addressing: The absolute worst case for a lookup is as bad as that in an unsorted list; however, this is not usually a problem, because programs generally perform large numbers of lookups, and the performance that the user observes is therefore equal to the probabilistic average. An example of the latter system is the case in point, a remailer: If a message is delayed unduly, the sender is unlikely to be contented by the fact that many other users' messages were serviced with considerably greater promptness. Therefore, the probabilistic distribution of service times is as important a metric of a remailer's performance as the probabilistic average service time. It may thus be quite reasonable to build in a hard cutoff in service time, such that any message that has been delayed by more than a set amount will be guaranteed to be sent on the next transmission. For some user of the remailer, this will make an observable improvement in performance; and since the extreme delay which triggers the expedited transmission is an unpredictable and infrequent event, it will not make cryptanalysis of the remailer any easier. JD -----BEGIN PGP SIGNATURE----- Version: 2.6 iQCVAgUBLkaHjEGHwsdH+oN9AQGOjAP/eCDAPlVfsdzB7HsBO5FLmFaxt5udMAPE UrFYw1EvrFP8gbMd6976dU6+o/A6xtDbZXCN8UOX5SYsY4+ixWxR3X5x86f4VAPi BowglJWs9hrGH/iSGH1tk2+ehbpFNKA4vUlvRtjKfX5vudYr5+fHWjCndFiVTo6K VXy0N2iQI4U= =uTv6 -----END PGP SIGNATURE-----