Editing Network service access point address

{{Short description|Identifying label for a Service Access Point used in Open Systems Interconnection networking}}
{{Redirect|NSAP|the former Swedish fascist party|National Socialist Workers' Party (Sweden)}}
{{Context|date=October 2009}}

A '''network service access point address''' ('''NSAP address'''), defined in ISO/IEC 8348, is an identifying label for a [[service access point]] (SAP) used in [[OSI model|OSI]] networking.

These are roughly comparable to [[IP address]]es used in the [[Internet Protocol]]; they can specify a piece of equipment connected to an [[Asynchronous Transfer Mode]] (ATM) network. A specific stream, analogous to a TCP/IP [[Computer port (software)|port]] or [[Berkeley sockets|socket]], 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]] (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 telephone numbers.

NSAP addresses do not specify where a network terminal is located. [[Routing]] equipment must translate NSAP addresses to subnetwork points of attachment (SNPAs) to route OSI packets; [[virtual circuit identifier]] (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]] 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]] 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: 
* [[Asynchronous Transfer Mode|ATM]] switched virtual circuit networks
* [[X.25]]  (see [[ITU-T]] [[X.121]] for addressing in public data networks)
* [[Frame Relay]]
* [[IS-IS]]
* [[Synchronous Digital Hierarchy]] and [[Synchronous Optical Networking]] networks.

NSAP-style addresses are used in the [[IS-IS]] routing protocol.

==Network selector==
The network selector (NSEL) is a field in the NSAP address that identifies the [[network layer]] service to which a packet should be sent. This part of the address for a router will always be 0x00. In the [[IS-IS]] routing protocol, the field is sometimes referred to as the SEL field.<ref>{{cite web|url=http://www.ciscopress.com/articles/article.asp?p=101756&rl=1|title=Intermediate System-to-Intermediate System (IS-IS) Basics for the Cisco BSCI Exam}}</ref><ref>{{cite web|url=http://safari.ciscopress.com/1587200856/gloss01|title=Cisco Press - 1587200856 - CCNP BSCI Exam Certification Guide, Third Edition}}</ref>

==See also==
*[[Address Resolution Protocol]]

==References==
{{reflist}}

{{DEFAULTSORT:Nsap Address}}
[[Category:OSI protocols]]
[[Category:Identifiers]]
[[Category:Network addressing]]