In a previous paper, one of the authors gave a worst case analysis for
the early packet discard (EPD) technique fur maintaining packet integ
rity during overload in ATM switches. This analysis showed that to ens
ure 100% goodput during overload under worst case conditions requires
a buffer with enough storage for one maximum length packet from every
active virtual circuit. This paper refines that analysis, using assump
tions that are closer to what we expect to see in practice, and examin
es how EPD performs when the buffer is not large enough to achieve 100
% goodput, We show that 100% goodput can be achieved with substantiall
y smaller buffers than predicted by the worst Ease analysis, although
the required buffer spate can be significant when the link speed is su
bstantially higher than the rate of the individual virtual circuits. W
e also show that high goodputs can be achieved with more modest buffer
sizes, but that EPD exhibits anomalies with respect to buffer capacit
y, in that there are situations in which increasing the amount of buff
ering can cause the goodput to decrease. These results are validated b
y comparison with simulation.