RFC 187 (rfc187) - Page 2 of 11

Network/440 Protocol Concept

INTRODUCTION

Network/44O is an experimental project in computer netting that was
undertaken by the Computer Science Department of IBM Research. The
primary objectives of the project have been to understand netting,
identify design problems and implement the solutions to these problems.

The above objectives have been met since a network has been built and is
presently being operated by the project. Implementation discussions
transpired with another department at Research in order to define a
realistic user system interface. The protocol defined for the project's
network is also the basis for the operation of an IBM OS network.

The Network/44O project has also been involved in the philosophical and
architectural concepts of network systems. The basic premise in our work
is the concept of a logical network machine.(1) The main theme is to
treat all systems involved in the network as a part of a single (large)
multiprocessor system. Although many of the ideas have been based on
hypothetical concepts, an equal number of ideas were derived from our
network implementation and operating experience.

The scope of this paper is to describe the philosophy and definition of
a network protocol that is not restricted to any physical configuration.
This is exemploified by the fact that a major portion of the ideas are
implemented in IBM's two major operational networks, one of which is a
distributed configuration and the other a star configuration.

(1) Intenet - Report 2, February 1, 1970, Computer Science Department,
    IBM Corporation, T. J. Watson Research Center, Yorktown Heights,
    New York.

BASIC ASSUMPTIONS

There was a necessity to delineate many network functions in setting up
an operating protocol. These functions included switching control,
buffer control, message control, and operating control. The operating
control function becomes further complicated as the user is able to
program the network as if it were a single operating system. The
protocol had to be further broken dowm into detailed functions in order
to cope with error recovery and handling techniques.

The original thoughts on handling these functions were to provide two
basic realms of control. The net control is a higher level function that
recognizes and controls all aspects of net jobs and the execution of job
steps in the network machine. In addition, a communication control
facility (referred to as an "Express Interpreter") was incorporated to
provide fast service for all messages that were to be moved between user
systems without intervention by the net controller.