A Network Service Access Point (NSAP) addresses, defined in ISO/IEC 8348, are identifying labels for network endpoints used in OSI networking.

These are roughly comparable to IP addresses used in the IP protocol; they specify a piece of equipment connected to the ATM network. A specific stream (analogous to a 'port' or 'socket' used with TCP or UDP) is specified by using a TSAP, or Transport Service Access Point. ATM can also use a Presentation and Session AP (PSAP and SSAP respectively), but these may also be left blank; this is up to the application.

NSAP addresses are allocated by the ISO, through a system of delegated authorities, which are generally national standards organizations. One of the schemes to generate NSAPs uses E.164 which is the addressing format describing phone numbers.

NSAP addresses do not specify where a network terminal is located. Routing equipment must translate NSAP addresses to NSPAs (Network Service Point Addresses) to route OSI packets; VCI (Virtual Circuit Identifier) numbers are an example of a datalink layer NSPAs in ATM; when OSI packets are sent encapsulated in IP packets the IP address is considered an NSPA.

NSAP addresses are used in the following OSI-based network technologies:

• ATM switched virtual circuit networks
• X.25 (see ITU-T X.121 for addressing in public data networks)
• Frame relay

and there are probably many more...

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