Performance Evaluation of ATM Shortcut Connections 
                 in Overlaid IP/ATM Networks

            Victor Firoiu, Jim Kurose, Don Towsley


                         ABSTRACT


In this paper we present methods to evaluate the benefit of using
direct ATM connections (shortcuts) between IP nodes in IP over ATM
networks, and we evaluate the benefit of ATM shortcuts for several
networks.  We model an IP/ATM network with and without ATM shortcuts
as two loss networks.  We propose a metric, the Network Load Ratio,
for network performance comparison, that gives the ratio of the number
of flows accepted by two networks at the same network blocking
probability.  We derive an estimator of this metric, the Asymptotic
Load Ratio, that has low computational complexity.  We use this
estimator as a basis for a methodology for network performance
comparison, and use it to evaluate the benefit of ATM shortcuts in
several concrete scenarios.