AService Access Point (SAP) is an identifying label for network endpoints used inOpen Systems Interconnection (OSI) networking.
The SAP is a conceptual location at which one OSI layer can request the services of another OSI layer. As an example, PD-SAP or PLME-SAP inIEEE 802.15.4 can be mentioned, where themedium access control (MAC) layer requests certain services from thephysical layer. Service access points are also used inIEEE 802.2Logical Link Control inEthernet and similardata link layer protocols.
When using the OSINetwork system (CONS orCLNS), the base for constructing an address for a network element is anNSAP address, similar in concept to anIP address. OSI protocols as well asAsynchronous 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:
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