ABSTRACT
We consider a distributed computer system in Wardrop equilibrium, i.e., situations where no
user can reduce its own response time by unilaterally choosing another path, if all the other users
retain their present paths. The Braess paradox is a famous example of paradoxical cases where
adding capacity to a network degrades the performance of all users. This study examines
numerically some examples around the Braess-like paradox in a distributed computer system.
We found that Braess’s paradox can occur, namely in equilibrium the mean job response time in
the network after adding a communication line for the sharing of jobs between nodes, for some
system parameter setting, can be greater than the mean job response time in the network before
adding the communication line. Indeed, two different types of paradox called weak and strong
paradox have been characterized. In the range of parameter values examined, the worst case
ratio of performance degradation obtained in the examined network model is about 75% and
65% for the cases of weak and strong paradox respectively.
Keywords: Braess Paradox, Wardrop Equilibrium, Distributed Computer Systems, Load
Balancing, Performance Evaluation, Non-cooperative Networks.