DCN Local-Network Protocols (RFC0891)
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2019-Feb-13
Internet Society Requests For Comment (RFCs)
This RFC provides a description of the DCN protocols for maintaining connectivity, routing, and clock information in a local network. These procedures may be of interest to the designers and implementers of other local networks.
Network Working Group D.L. Mills Request for Comments: 891 December 1983
DCN Local-Network Protocols
This RFC is a description of the protocol used in the DCN local networks to maintain connectivity, routing, and timekeeping information. These procedures may be of interest to designers and implementers of other networks.
This document describes the local-net architecture and protocols of the Distributed Computer Network (DCN), a family of local nets based on Internet technology and an implementation of PDP11-based software called the Fuzzball. DCN local nets have been in operation for about three years and now include clones in the USA, UK, Norway and West Germany. They typically include a number of PDP11 or LSI-11 Fuzzballs, one of which is elected a gateway, and often include other Internet-compatible hosts as well.
The DCN local-net protocols are intended to provide connectivity, routing and timekeeping functions for a set of randomly connected personal computers and service hosts. The design philosophy guiding the Fuzzball implementation is to incorporate complete functionality in every host, which can serve as a packet switch, gateway and service host all at the same time. When a set of Fuzzballs are connected together using a haphazard collection of serial, parallel and contention-bus interfaces, they organize themselves into a network with routing based on minimum delay.
The purpose of this document is to describe the local-net protocols used by the DCN to maintain connectivity, routing and timekeeping functions. The document is an extensive revision and expansion of Section 4.2 of  and is divided into two parts, the first of which is an informal description of the architecture, together with explanatory remarks. The second part consists of a semi-formal specification of the entities and protocols used to determine connectivity, establish routing and maintain clock synchronization and is designed to aid in the implementation of cohort systems. The link-level coding is described in the appendix.
2. Narrative Description
The DCN architecture is designed for local nets of up to 256 hosts and gateways using the Internet Protocol (IP) and client protocols. It provides adaptive routing and clock synchronization functions in an arbitrary topology including point-to-point links and multipoint bus systems. It is intended for use in connecting personal computers to each other and to service machines, gateways and other hosts of the Internet community. However, it is not intended for use in large, complex networks and does not support the sophisticated routing and control algorithms of, for example, the ARPANET.
A brief description of the process and addressing structure used in the DCN may be useful in the following. A DCN physical host is a PDP11-compatible processor which supports a number of cooperating sequential processes, each of
DCN Local-Network Protocols Page 2 D.L. Mills
which is given a unique 8-bit identifier calle...