INDUSTRIAL ENGINEERING AND
OPERATIONS RESEARCH
PRESENTS
IEOR MONDAY SEMINAR
The Impact of Reneging in Processor Sharing
Queues
Bert Zwart
Department of Mathematics and Computer Science
ABSTRACT
Processor Sharing (PS) queues were originally
introduced to analyze the performance of time-sharing in computer networks.
Nowadays, PS queues are one of the most popular congestion models for TCP
traffic on the Internet. Under the PS discipline, each customer in the system
receives the same service rate.
Motivated by obtaining a better understanding of the impact of reneging (e.g.
aborting the download of a file) in communication networks, we consider a PS
queue in overload where customers may leave after a certain amount of time,
before their service is finished. Under the PS service discipline, such behavior
is unwelcome, since it always implies that some work is done in vain.
Therefore, when the queue is in overload, the actual throughput can be much
lower than the total service rate.
We consider a fluid approximation of this queue, which is
accurate when both the arrival rate and service rate is large. We apply this
fluid approximation to analyze the impact of reneging on system performance in
PS queues. By studying several examples, we show that the impact can be quite
substantial and propose an admission control scheme to reduce its effect.
This talk is based on joint work with Christian Gromoll
(Stanford) and Philippe Robert (INRIA).
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