We analyse the deviant behavior of a queue fed by a large number of traffic
streams. In particular, we explicitly give the most likely trajectory (or
'optimal path') to buffer overflow, by applying large deviations techniques
. This is done for a broad class of sources, consisting of Markov fluid sou
rces and periodic sources. Apart from a number of ramifications of this res
ult, we present guidelines for the numerical evaluation of the optimal path
.