High-level protocols

High-level protocols (HLP's) are the high-level languages of distributed systems. In a resource-sharing network, HLP's link processes working on a conmmn application. The design of an HLP is decomposed into three components: language, coding, and transport. The language expresses the commands and data passed between processes. It is designed to provide standardization and device independence, in order to use a small number of HLP's to address a range of applications implemented on a variety of computer systems. Coding converts the language into digital messages. Finally, a transport system is used to transmit the messages from one process to another-experience with HLP's has shown that different HLP's require different transport behaviors. This paper describes some examples of HLP's (ARPA network voice and graphics protocols), and argues that modern techniques for expressing structure and control in programming languages should be applied to analogous problems in communication among application processes in a network.