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 assigned to a device connected to a computer network that uses the Internet Protocol for communication. IP addresses serve two main functions: network interface i ...

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. IP ...

; they can specify a piece of equipment connected to an

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital trans ...

(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 Hamburg, Manch ...

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 hexag ...

, is specified by using a transport service access point (

TSAP 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, ...

). 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 independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. M ...

(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 netw ...

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 theory, 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 ...

equipment must translate NSAP addresses to subnetwork points of attachment (SNPAs) to route OSI packets;

virtual circuit identifier Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital tran ...

(VCI) 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.

Synchronous Digital Hierarchy 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 diod ...

Synchronous Optical Networking 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 di ...

networks are a major part of the network infrastructure, and NSAPs are used extensively. They are usually assigned by the network management/

network operations centre A network operations center (NOC, pronounced like the word ''knock''), also known as a "network management center", is one or more locations from which network monitoring and control, or network management, is exercised over a computer, telecom ...

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 switched virtual circuit networks *

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

(see

ITU-T The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...

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 Network, public data networks (PDNs), connecting two network user addresses (NUAs). It consists of ...

for addressing in public data networks) *

Frame Relay Frame Relay (FR) is a standardized wide area network (WAN) technology that specifies the Physical layer, physical and data link layers of digital telecommunications channels using a packet switching methodology. Frame Relay was originally devel ...

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 thi ...

and

networks. NSAP-style addresses are used in the

routing protocol.

Network selector

The network selector (NSEL) 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 Router (computing), routers. Functions The network layer provides t ...

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

{{DEFAULTSORT:Nsap Address OSI protocols Identifiers Network addressing

Allocation and scope

Network selector

See also

References