Packet network simulation: speedup and accuracy versus timing granularity

This paper describes a new technique that can speedup simulation of high-speed, wide-area packet networks by one to two orders of magnitude. Speedup is achieved by coarsening the representation of network traffic from packet-by-packet to train-by-train, where a train represents a cluster of closely spaced packets. Coarsening the timing granularity creates longer trains and makes the simulation proceed more quickly since the cost of processing trains is independent of train size. Coarsening the timing granularity introduces, of course, a degree of approximation. This paper presents experiments that evaluate our coarse time-grain simulation technique for first in/first out (FIFO) switched, TCP/IP, and asynchronous transfer mode (ATM) networks carrying a mix of data and streaming traffic. We show that delay, throughput, and loss rate can frequently be estimated within a few percent via coarse time-grain simulation. This paper also describes how to apply coarse time-grain simulation to other switch disciplines. Finally, this paper introduces three more simulation techniques which together can double the performance of well written packet simulators without trading with the simulation accuracy. These techniques reduce the number of outstanding simulation events and reduce the cost of manipulating the event list.