OSI/AS Configuration and Management Manual

NSAP Addressing

OSI/AS Configuration and Management Manual—424119-001

3-4

NSAP Addresses

An NSAP (network service access point) address (sometimes called a network address

or a global network address) is used by the Network Layer to identify the Transport

Layer user of its service. NSAP addresses are globally unique values within the OSI

network, and are administered by a hierarchy of addressing authorities as established by

a hierarchy of addressing domains (discussed in the following subsections):

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Network Addressing Authorities on this page

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Network Addressing Domains on this page

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X25 1980 Versus 1984 Addressing on page 3-6

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Specifying NSAP Addresses in OSI/AS on page 3-8

Network Addressing Authorities

A network addressing authority is a set of rules. The authority can be a set of national or

international standards (such as the ISO standards) or a set of local rules issued by a

single person (such as a network manager). The network addressing authority ensures

the uniqueness of all the NSAP addresses within a domain (discussed in Network

Addressing Domains on page 3-4). There can be a hierarchy of authorities, each

authority governing its own domain and, in turn, regulated by its parent authority (which

in turn, may be regulated by its parent authority, and so on).

Each addressing authority is independent of other addressing authorities on the same

hierarchical level. The highest addressing authority is the one that governs the global

network addressing domain. This authority is defined in ISO 8348, Addendum 2.

Network Addressing Domains

The set of rules that makes up a network addressing authority has jurisdiction over a

portion of the network, known as a network addressing domain. Each network

addressing domain is governed by a single network addressing authority. Every NSAP

address, therefore, is within a network addressing domain. Each network addressing

domain is, in turn, within a hierarchically higher network addressing domain, which is

again within a higher domain, and so on. The highest domain is the global network

addressing domain, which encompasses all NSAP addresses in an OSI network. A

network may include many or few addressing domains.