Functional Description of the Systems Communications Architecture

This document, revised on November 21, 1983, serves as a functional specification for the Systems Communications Architecture (SCA) specifically for the TOPS-20 operating system. It details the module's role as a multiplexer/demultiplexer for Computer Interconnect (CI) virtual connections. The document outlines the differences between the corporate SCA specification and the TOPS-20 implementation, describes data structures such as system and connect blocks, and defines the interfaces for both monitor-level and JSYS-level system applications (SYSAPs). It includes comprehensive information on error codes, buffer management, message and datagram handling, and callback mechanisms required for reliable communications across the CI network.