Maintenance Operation Protocol Functional Specification

This document is the Maintenance Operation Protocol (MOP) Functional Specification (Phase III), Version 2.1.0, published by Digital Equipment Corporation in October 1980.

It describes the Maintenance Operation Protocol (MOP), an optional component of the DECnet DIGITAL Network Architecture (DNA), specifically operating within its data link layer.

MOP provides a set of messages and rules for key maintenance and control functions, including:

• Loading computer memory (down-line loading)
• Dumping computer memory
• Testing data links
• Controlling unattended remote computer systems (forcing them into MOP mode)
• Transferring control to programs resident in memory.

MOP defines the communication and interactions between a "host" system (which initiates functions) and a "satellite" system (the target of these functions), operating over a physical communications link in alternate half-duplex mode. It relies on an underlying data link control procedure, typically the Digital Data Communications Message Protocol (DDCMP) within DECnet, for message framing and bit error detection. The document provides technical detail for implementers and general information for evaluation of the protocol.