9 - Open systems interconnection model

Abstract

This chapter discusses in the fundamental concepts of open systems interconnection (OSI) model. The purpose of the OSI reference model is to provide a common basis for the development of systems interconnection standards. An open system is a system that conforms to specifications and guidelines, which are “open” to all. This enables equipment from various manufacturers, who claim compliance to a standard, to be used interchangeably on a network using that standard. OSI simplifies data communications into a hierarchy of seven layers. Each layer has a defined purpose, which is dependent on and interfaces with, the layer above and below it. Standards are defined for each layer in a way that it allows some flexibility enabling system designers to develop independent protocol layers. The OSI model framework specifically and clearly defines the functions or services that have to be provided at each of the seven layers. This chapter describes data communications for instrumentation and control, and describes in detail seven layers of the OSI reference model.