Service Primitives

A service is formally specified by a set of primitives (operations) available to a user or other entity to access the service. These primitives tell the service to perform some action or report on an action taken by a peer entity. Service primitives are divided into four classes. They are:

Operations	Meaning
Request	An entity wants the service to do some work
Indication	An entity is to be informed about an event
Response	An entity wants to respond to an event
Confirm	The response to an earlier request has come back