Performance of Asynchronous, Variable Bit Rate Communications over ATM: A Comparison with FDDI

Asynchronous Transfer Mode (ATM) technology performance is evaluated for Class C (variable bit rate, asynchronous) data transfer, as would be typically found when migrating legacy applications to an ATM environment. Of particular interest are the end-to-end latencies obtainable using ATM networks to transfer time critical data. Latencies obtained using Classical IP over ATM and raw ATM using the Fore ATM API are compared to performance of traditional TCP/IP on equivalent FDDI networks. It is shown that at OC-3, in it’s simplest configuration of back to back nodes, Classical IP over ATM latencies are greater than those obtained using FDDI, particularly at small message sizes. However, the results show that IP over ATM via ATM switches can exhibit better performance than FDDI switches or routers, due to the optimization of the ATM switch for fixed size cells. Thus, these benchmarks confirm that ATM provides a good foundation for building high performance IP internetworks. Using raw AAL 3/4 ATM, significantly lower latencies than the equivalent IP over ATM results or traditional FDDI results are presented, both in back-to-back configurations and through network devices such as switches and routers. A discussion of tradeoffs associated with using FDDI versus ATM for mission critical, real time data transfer applications is also included.