Introduction
Recommendation X.200 describes the Reference Model for open systems interconnection (OSI). It establishes
a framework for coordinating the development of existing and future Recommendations for the interconnection of
systems.
The objective of OSI is to permit the interconnection of heterogeneous computer systems so that useful
communication between application processes may be achieved. At various times, security controls must be established
in order to protect the information exchanged between the application processes. Such controls should make the cost of
improperly obtaining or modifying data greater than the potential value of so doing, or make the time required to obtain
the data improperly so great that the value of the data is lost.
This Recommendation defines the general security-related architectural elements which can be applied
appropriately in the circumstances for which protection of communication between open systems is required. It
establishes, within the framework of the Reference Model, guidelines and constraints to improve existing
Recommendations or to develop new Recommendations in the context of OSI in order to allow secure communications
and thus provide a consistent approach to security in OSI.
A background in security will be helpful in understanding this Recommendation. The reader who is not well
versed in security is advised to read Annex A first.
This Recommendation extends the Reference Model (Recommendation X.200) to cover security aspects which
are general architectural elements of communications protocols, but which are not discussed in the Reference Model.