Performance Evaluation of the ARPANET Transmission Control Protocol in a Local Area Network Environment

Samuel T. Chanson, K. Ravindran and Stella Atkins
Publishing date
July 1985

The Transmission Control Protocol (TCP) of ARPANET is one of the most popular transport level communication protocols in use today. Originally designed to handle unreliable and hostile subnets in a long-haul network TCP has been adopted by many local area networks (LAN) as well. It is, for example, available in 4.2 BSD UNIX for interface to Ethernet and several other LAN technologies. This is convenient but not desirable from a performance standpoint since the control structure is far more complex than is necessary for LANs. This paper describes what we learned in measuring and tuning the performance of TCP in transferring large files between two hosts of different speeds over the Ethernet. Models are presented which allow the optimal buffer size and the flow control parameter to be determined. Based on observed traffic patterns and those reported elsewhere, we formulated guidelines for the design of transport protocols for a single LAN environment. We then present a new, much simpler LAN transport level protocol which replaces TCP with significant improvement in network throughput. Internet packets will use the full TCP. This is done at the gateway. Since the majority of the packets in a LAN are for local usage, this scheme improves the overall network throughput rate as well as the mean packet delay time.