3.8.c [i] NSAP addressing
NSAP is the network-layer address for CLNS packets. An NSAP describes an attachment to a particular service at the network layer of a node, similar to the combination of IP destination address and IP protocol number in an IP packet. NSAP encoding and format are specified by ISO 8348/ Ad2.
ISO 8348/ Ad2 uses the concept of hierarchical addressing domains. The global domain is the highest level. This global domain is subdivided into sub-domains, and each sub-domain is associated with an addressing authority that has a unique plan for constructing NSAP addresses.
An NSAP address has two major parts: the initial domain part (IDP) and the domain specific part (DSP). The IDP consists of a 1-byte authority and format identifier (AFI) and a variable-length initial domain identifier (IDI), and the DSP is a string of digits identifying a particular transport implementation of a specified AFI authority.
Everything to the left of the system ID can be thought of as the area address of a network node.
The LSP identifier is derived from the system ID (along with the pseudonode ID and LSP number ). Each IS is usually configured with one NET and in one area; each system ID within an area must be unique.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 4277-4279). . Kindle Edition.