Page 737 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

OSI Model

Communications between computers over networks are made possible
by protocols. A protocol is a set of rules and restrictions that define
how data is transmitted over a network medium (e.g., twisted-pair

cable, wireless transmission). In the early days of network
development, many companies had their own proprietary protocols,
which meant interaction between computers of different vendors was
often difficult, if not impossible. In an effort to eliminate this problem,
the International Organization for Standardization (ISO) developed

the Open Systems Interconnection (OSI) Reference Model for
protocols in the early 1980s. Specifically, ISO 7498 defines the OSI
Reference Model (more commonly called the OSI model).
Understanding the OSI model and how it relates to network design,
deployment, and security is essential in preparing for the CISSP exam.

In order to properly implement secure design principles in network
architectures, it is important to fully understand all of the technologies

involved in computer communications. From hardware and software
to protocols and encryption and beyond, there are lots of details to
know, standards to understand, and procedures to follow.
Additionally, the basis of secure network architecture and design is a
thorough knowledge of the OSI and TCP/IP models as well as Internet
Protocol (IP) networking in general.

History of the OSI Model

The OSI model wasn’t the first or only attempt to streamline
networking protocols or establish a common communications
standard. In fact, the most widely used protocol today, TCP/IP (which
is based on the DARPA model, also known now as the TCP/IP model),
was developed in the early 1970s. The OSI model was not developed

until the late 1970s.

The OSI protocol was developed to establish a common
communication structure or standard for all computer systems. The
actual OSI protocol was never widely adopted, but the theory behind