A protocol simulator for the Thunder and Lightning ATM network

Abstract

Software simulators have often been used to test and validate new protocols, but the high bandwidth of newly emerging ATM networks implies prohibitive memory requirements. This paper describes several simulation techniques we have devised as part of the Thunder and Lightning project to build 40 and 100 gigabit per second ATM networks. L CPU BuffetAdvances in fiber-optic and VLSI technologies have led to the emergence of very highspeed networks based on the Asynchronous Transfer Mode (ATM) [5]. The University of California, Santa Barbara, is currently building 40 gigabit per second ATM networks and developing the technology for 100 gigabit per second A T M networks as part of its Thunder and Lightning project [I]. New protocols are being developed to take full advantage of the resources provided by the new switches.As part of the Thunder and Lightning protocol development effort, we have found it necessary to simulate the operation of our new protocols both to validate analytic results and to measure performance, subject to traffic patterns which cannot easily be dealt with analytically. While general simulation packages are available [2, 31, we found that they did not meet our needs. Most of the packages can simulate the switch but not the protocol, and few model the unique buffering strategy of the Thunder and Lightning switch. In addition, protocol correctness requirements for Thunder and Lightning allow us to make optimizations which significantly reduce the otherwise prohibitive memory requirements.Thus, we found it necessary to develop a network protocol simulator designed to meet our needs. Figure 1 depicts the architecture of one port in the Thunder and Lightning switch. The switch has four input ports and four output ports. Each output port contains three firstin first-out (FIFO) buffers corresponding to each of the other incoming ports; loopback is not allowed. In addition, a small buffer stores packets generated by the control processor governing that port's operation. Each FIFO is served at output rates set by the control protocol, with the exception that packets generated by the processor (control packets) are always given priority. Simulation ModelOne of the main objectives of the Thunder and Lightning project is to provide lossless communication, while using the full capacity of the switch links and not incurring the overhead required to make reservations. Consequently, the Thunder and Lightning switch possesses substantial buffering capacity; each FIFO can hold 100,OOO ATM cells.The primary goals of the simulation project are to investigate protocol correctness and 0-8186-7585-3/96 $5.00 0 1996 IEEE 28