Our society is heavily dependent on a wide variety of communication services. These services must be available even when undesirable events like sabotage, natural disasters, or network failures happen. The network survivability as defined by the ANSI T1A1.2 committee [1] is the transient performance from the instant an undesirable event occurs until steady state with an acceptable performance level is attained. In this paper we assess the survivability of a network with virtual connections

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... ed to link or node failures. We have developed both simulation and analytic models to cross validate our assumptions. In order to avoid state space explosion while addressing large networks we decompose our models first in space by studying the nodes independently and then in time by decoupling our analytic performance and recovery models which gives us a closed form solution. The modeling approaches are applied to two network examples. The results show very good correspondence between the transient loss and delay performance in our simulations and in the analytic approximations.