When we study the subject of computer network, we encounter many terminologies associated with the subject. Some terminologies are briefly described below.
1. Entity :: The active component in each layer are called entities. Entity can be a software process or hardware like an intelligent input/output device etc.
2. Peer Entity :: Entities in the same layer running on different machines are called peer entities.
3. Service provider and service user :: In a layered architecture, layer n provides a service which is used by layer n+1. Here layer n is service provider and layer n+1 is service user.
4. Service Access Point :: A layer n offers services to layer n+1 at a place which is called service access point. Each SAP has a unique address for identification.