High-performance TCP/IP and UDP/IP networking in DEC OSF/1 for Alpha AXP

Network speeds have been increasing rapidly. The higher bandwidth communication links available now, ranging from 100 Mbits/sec to Gbits/sec, present considerable potential for distributed applications. Processor speeds have also increased relentlessly. However, until now the ultimate throughput delivered to the user application has not increased as rapidly. The paper describes the implementation of the TCP/IP and UDP/IP protocol suite on Digital's Alpha AXP systems with the DEC OSF/1 operating system over FDDI. User applications are able to achieve almost the full FDDI bandwidth of 100 Mbits/sec, thus essentially eliminating the end-system as a bottleneck for network I/O bottleneck. Included in the TCP/IP implementation are extensions to TCP recently adopted by the IETF such as support for large transport windows for higher performance. This is particularly desirable for high speed networks and/or large delay networks. Incremental work for data movement and checksums are often the most expensive operations of protocol processing. These have been optimized to take advantage of the Alpha XP workstation architecture including 64 bit support, wider cache lines and the coherence of cache blocks with DMA. We show, via measurement results that TCP achieves a throughput of 95 Mbits/sec. We also show that UDP performance is comparable. In addition, and unlike typical BSD-derived systems, the UDP receive throughput to user applications is also maintained at high load.<<ETX>>