ISO 7498-2:1989 provides a general description of security services and related mechanisms, which can be ensured by the Reference Model, and of the positions within the Reference Model where the services and mechanisms may be provided. Extends the field of application of ISO 7498 to cover secure communications between open systems. Adds to the concepts and principles included in ISO 7498 but does not modify them. Is no implementation specification, nor a basis for assessing the conformance of actual implementations.