  We present a model of performance bound calculus on feedforward networks
where data packets are routed under wormhole routing discipline. We are
interested in determining maximum end-to-end delays and backlogs of messages or
packets going from a source node to a destination node, through a given virtual
path in the network. Our objective here is to give a network calculus approach
for calculating the performance bounds. First we propose a new concept of
curves that we call packet curves. The curves permit to model constraints on
packet lengths of a given data flow, when the lengths are allowed to be
different. Second, we use this new concept to propose an approach for
calculating residual services for data flows served under non preemptive
service disciplines. Third, we model a binary switch (with two input ports and
two output ports), where data is served under wormhole discipline. We present
our approach for computing the residual services and deduce the worst case
bounds for flows passing through a wormhole binary switch. Finally, we
illustrate this approach in numerical examples, and show how to extend it to
feedforward networks.
