66 Simulation Technologies in Networking and Communications
transition depends critically on the details of the model. Also, systems with larger buf-
fers tend to have rst-order transition.
4. An interesting feature of the rst-order phase transitions is that the network behavior fol-
lows the second-order approximation very closely until the load reaches the critical value.
When it happened, the network goes to the saturation state abruptly. It is very difcult to
predict when it can happen even from the simulation data: there are no signicant increases
in the average latency or queue length right before the critical point. Only the observation
of the uctuations of average number of the messages in the network during the simula-
tion can ...