Service Access Point

A Service Access Point (SAP) is an identifying label for network endpoints used in Open Systems Interconnection (OSI) networking.

As an example, PD-SAP or PLME-SAP in IEEE 802.15.4 can be mentioned, where the medium access control (MAC) layer requests certain services from the physical layer.

OSI protocols as well as Asynchronous Transfer Mode (ATM) can use Transport (TSAP), Session (SSAP) or Presentation (PSAP) Service Access Points to specify a destination address for a connection.

These SAPs consist of NSAP addresses combined with optional transport, session and presentation selectors, which can differentiate at any of the three layers between multiple services at that layer provided by a network element.

IEEE 802's reference model (RM) guarantees the following SAPs:[1] 802.3 (the Ethernet standard) optionally includes:

Side-by-side comparison between the OSI (left) and IEEE 802 (right) reference models