A Service Access Point is an identifying label for network endpoints used in Open Systems Interconnection

Open Systems Interconnection

Open Systems Interconnection is an effort to standardize networking that was started in 1977 by the International Organization for Standardization , along with the ITU-T.-History:...

 (OSI) networking.

When using the OSI Network Layer

Network Layer

The network layer is layer 3 of the seven-layer OSI model of computer networking.The network layer is responsible for packet forwarding including routing through intermediate routers, whereas the data link layer is responsible for media access control, flow control and error checking.The network...

 (CONS

CONS

CONS, Connection-Oriented Network Service, is one of the two OSI network layer protocols, the other being CLNS...

 or CLNS

CLNS

CLNS is an abbreviation of Connectionless Network Service.It is an OSI Network Layer service that does not require a circuit to be established before data is transmitted...

), the base for constructing an address for a network element is an NSAP address

NSAP address

A Network Service Access Point address , defined in ISO/IEC 8348, is an identifying label for a Service Access Point used in OSI networking....

, similar in concept to an IP address

IP address

An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...

. OSI Application Layer

Application layer

The Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer....

 protocols as well as Asynchronous Transfer Mode

Asynchronous Transfer Mode

Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...

 (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.

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 in IEEE 802.15.4 can be mentioned, where the Media Access Control

Media Access Control

The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...

 (MAC) layer requests certain services from the Physical Layer

Physical layer

The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....

. Service access points are also used in IEEE 802.2

IEEE 802.2

IEEE 802.2 is the IEEE 802 standard defining Logical Link Control , which is the upper portion of the data link layer of the OSI Model. The LLC sublayer presents a uniform interface to the user of the data link service, usually the network layer...

 Logical Link Control

Logical Link Control

The logical link control data communication protocol layer is the upper sub-layer of the data link layer in the seven-layer OSI reference model...

 in Ethernet

Ethernet

Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

 and similar Data Link Layer

Data link layer

The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....

protocols.

The TSAP is an expansion of the NSAP.