The authors report a preliminary analysis of the processing overhead of the transport protocol TCP (Transmission Control Protocol) in which they estimate the possible performance range of the protocol. The analysis was performed by compiling a version of TCP and counting the number of the instructions in the common path. The analysis suggests that fewer than 200 instructions are required to process a TCP packet in the normal case. This number is small enough to support very high-speed transmission if it were the major overhead. The authors offer some speculations about the actual source of processing overhead in network protocols.>

A desktop personal computer can be greatly extended in usefulness by attaching it to a local area network and implementing a full set of network protocols, just as one might provide for a mainframe computer. Such protocols are a set of tools that allow the desktop computer not just to access data elsewhere, but to participate in the computing milieu much more intensely. There are two challenges to this proposal. First, a personal computer may often be disconnected from the network, so it cannot track the network state and it must be able to discover and resynchronize with that state very quickly. Second, full protocol implementations have often been large and slow, two attributes that could be fatal in a small computer. This paper reports a network implementation for the IBM Personal Computer that uses several performance-oriented design techniques with wide applicability: an upcall/downcall organization that simplifies structure; implementation layers that do not always coincide with protocol specification layers; copy minimization; and tailoring of protocol implementations with knowledge of the application that will use them. The size and scale of the resulting package of programs, now in use in our laboratory for two years, is quite reasonable for a desktop computer and the techniques developed are applicable to a wider range of network protocol designs.