  The deterministic network calculus offers an elegant framework for
determining delays and backlog in a network with deterministic service
guarantees to individual traffic flows. This paper addresses the problem of
extending the network calculus to a probabilistic framework with statistical
service guarantees. Here, the key difficulty relates to expressing, in a
statistical setting, an end-to-end (network) service curve as a concatenation
of per-node service curves. The notion of an effective service curve is
developed as a probabilistic bound on the service received by an individual
flow. It is shown that per-node effective service curves can be concatenated to
yield a network effective service curve.
