A Network Service Access Point address (NSAP address), defined in ISO/IEC 8348, is an identifying label for a

Service Access Point A Service Access Point (SAP) is an identifying label for network endpoints used in Open 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, ...

(SAP) used in OSI networking. These are roughly comparable to

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

es used in the

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

; they can specify a piece of equipment connected to an

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs o ...

(ATM) network. A specific stream, analogous to a TCP/IP

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as ...

socket Socket may refer to: Mechanics * Socket wrench, a type of wrench that uses separate, removable sockets to fit different sizes of nuts and bolts * Socket head screw, a screw (or bolt) with a cylindrical head containing a socket into which the hexa ...

, is specified by using a Transport Service Access Point ( TSAP). ATM can also use a Presentation (PSAP) and Session (SSAP) Access Point, but these may also be unspecified; this is up to the application.

Allocation and scope

NSAP addresses are allocated by the

International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...

(ISO), through a system of delegated authorities, which are generally national standards organizations. One of the schemes to generate NSAPs uses

E.164 E.164 is an international standard (ITU-T Recommendation), titled ''The international public telecommunication numbering plan'', that defines a numbering plan for the worldwide public switched telephone network (PSTN) and some other data network ...

which is the addressing format describing telephone numbers. NSAP addresses do not specify where a network terminal is located.

Routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...

equipment must translate NSAP addresses to SNPAs (SubNetwork Point of Attachment) to route OSI packets; VCI (virtual circuit identifier) numbers are an example of a datalink layer SNPAs in ATM; when OSI packets are sent encapsulated in IP packets the IP address is considered an SNPA. Currently SDH/SONET networks are a major part of the network infrastructure and NSAPs are used extensively. They are usually assigned by the Network Management/NOC personnel and agreed upon within an organization to be unique (to that organization and based on geographical location using country code telephone prefixes) and are required before any operational connectivity is established at the commissioning stage. NSAP addresses are used in the following OSI-based network technologies: *

ATM ATM or atm often refers to: * Atmosphere (unit) or atm, a unit of atmospheric pressure * Automated teller machine, a cash dispenser or cash machine ATM or atm may also refer to: Computing * ATM (computer), a ZX Spectrum clone developed in Mo ...

switched virtual circuit networks *

X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts a ...

(see

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...

X.121 X.121 is the ITU-T address format of the X.25 protocol suite used as part of call setup to establish a switched virtual circuit between Public Data Networks (PDNs), connecting two network user addresses (NUAs). It consists of a maximum of fo ...

for addressing in public data networks) *

Frame Relay Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated ...

IS-IS Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this b ...

SDH SDH may refer to: Science, medicine and technology * Serine dehydratase, an enzyme * L-sorbose 1-dehydrogenase, an enzyme * Succinate dehydrogenase, an enzyme * Shubnikov–de Haas effect * Social Determinants of Health, economic and social condi ...

SONET Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting dio ...

networks. NSAP-style addresses are used in the

routing protocol.

NSEL

The NSEL (Network-Selector) is a field in the NSAP address that identifies the

network layer In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of trans ...

service to which a packet should be sent. This part of the address for a router will always be 0x00. In the

routing protocol, the field is sometimes referred to as the SEL field.

References

OSI protocols Identifiers Network addressing {{network-software-stub

Allocation and scope

NSEL

See also

References