This Recommendation | International Standard defines the OSI Physical Service in terms of: a) the primitive actions and events of the Service; b) the parameters associated with each primitive action and event, and the form which they take; c) the interrelationship between, and the valid sequences of, these actions and events. The principal objective of this Recommendation | International Standard is to specify the characteristics of a conceptual Physical Service and thus supplement the OSI Basic Reference Model in guiding the development of Physical Layer protocols. This Recommendation | International Standard does not specify individual implementations or products nor does it constrain the implementation of entities and interfaces within an information processing system. There is no conformance of equipment to this Recommendation | International Standard. Instead, conformance is achieved through implementation of conforming OSI Physical protocols that fulfil the Physical Service defined in this Recommendation | International Standard.