The definition of IBM's Systems Network Architecture (SNA) has evolved into a specification of a node in the form of a metaimplementation using formal, state-oriented descriptive techniques. This evolution is traced here, and the different formal techniques are described. The culmination of this process has been the development of a PL/I-based programming language, Format and Protocol Language (FAPL), as a descriptive tool. Using FAPL, the architects now define SNA by a programmed meta-implementation of a node. In this form, it is precise, readily accessible to the implementing product designers and programmers, and structurally close to the implementations. The essential features of the meta-implementation and of FAPL are described, along with the implications and advantages of describing the architecture in an executable form. One major benefit, already being realized, is the capability to test the logical consistency and completeness of the executable description itself. The current status of the validation of the executable description and sample results obtained are described.

A stochastic model is developed for the process of dynamic buffering for inbound messages in a computer communications system.For a specific characterization of message traffic, complementary viewpoints--one considering the process as a queueing system, the other considering it as a compound process--lead to the same probability generating function.Two buffer assignment schemes, both dynamic but differing in binding strategy, are compared in terms of optimal buffer size and total buffer pool requirements for a given overflow criterion.A simple model of optimal blocking, earlier proposed by Gaver and Lewis, is extended to cover both buffer strategies and also heterogeneous message sources.Finally, the derived characterization of total storage requirements is compared by numerical example with conservative and nonconservative asymptotic treatments of the process.