High-speed ATM networking on low-end computer systems

The practicability of high-speed communication on low-end systems has frequently been questioned and even less demanding variants of high-speed networking standards have been developed to accommodate for the restrictions of contemporary personal computers. In this paper, architectural aspects of existing PC hardware, ATM network adapters, and operating systems are examined, and in fact, serious limitations are discovered. Primarily memory bandwidth is found to be insufficient to support the number of transfers required by traditional networking implementation designs, plus the number of further accesses required for data processing by the sending or the receiving application. The use of single-copy, a concept well known from higher-end systems, is proposed as a means to overcome the memory bandwidth bottleneck. Not only usage scenarios in which single-copy can be reasonably applied, but also situations in which single-copy would yield only marginal improvements or where performance could even deteriorate are identified. Furthermore, implementation issues, such as locking of shared user pages, are discussed. Finally, the performance of single-copy is tested in an implementation of ATM support on Linux, done at LRC, by measuring uni- and bidirectional AAL5 throughput with different PDU sizes. The measurement results indicate that high-speed communication is feasible on today's low-end systems for applications which are primarily uni-directional in nature, and which respect alignment and access constraints imposed by optimizations like single-copy.