Introduction

While involved in attempting to specify the formal protocol, we also attempted to formulate a prototypical NCP in an Algol-like language. After some weeks of concentrated effort, the project was abandoned as we realized that the code was becoming unreadable. We still, however, felt the need to demonstrate our conception of how an NCP might be implemented; we felt that this would help suggest solutions for problems that might arise in trying to mold the formal specifications into an existing system. This document is that attempt to specify in a prose format what an NCP could look like.

There are obvious limitations on a project of this nature. We do not, and cannot, know all of the quirks of the various systems that must write an NCP. We are forced to make some assumptions about the environment, system calls, and the like. We have tried to be as general as possible, but no doubt many sites will have completely different ways of conceptualizing the NCP. There is great difficulty involved in conveying our concepts and the mechanisms that deal with these concepts to people who have wholly different ways of looking at things. We have, however, benefited greatly by trying to actually code this program for our fictitious machine. Many unforeseen problems surfaced during the coding, and we hope that by issuing this document we can help to alleviate similar problems which may arise in individual cases.

There is, of course, absolutely no requirement to implement anything which is contained in this document. The only rigid rules which an NCP must conform to are stated in NWG/RFC#54. This description is intended only as an example, not as a model.

In the discussion which follows we first describe the environment to be assumed and postulate a set of system calls. We discuss the overall architecture of the NCP and the tables that will be used to hold relevant information. Narratives of network operations follow. A state diagram is then presented as a convenient method for conceptualizing the cause-effect sequencing of events. The detailed processing of each type of network event (system calls or incoming network messages) is then discussed.