Installing and Administering OSI Transport Services

48 Chapter 1
HP OTS/9000 Resources
Structure of NSAP Addresses
• Take into account the needs of different network types (individual or
“small,” sophisticated or “big,” and intermediate).
• Facilitate efficient routing in private networks.
• Provide a strategy that takes advantage of dynamic routing protocols
such as ES-IS and the emerging IS-IS protocols.
• Minimize the risk of re-structuring, due to present lack of universally
accepted standards for NSAP structures.
• Minimize the risk of re-allocation of values, due to present lack of
administrative authorities.
• Propose a method for automatic allocation of unique NSAP addresses.
The Syntax of an NSAP Address
An NSAP, as defined by ISO, has several characteristics. It may be one to
twenty octets (bytes) in length. It is composed of two parts: the Initial
Domain Part (IDP) and the Domain Specific Part (DSP). The DSP may
also be partitioned into several fields. These fields and their sizes are
defined by the authority that controls the IDP.
Figure 1-8
The Initial Domain Part
The IDP portion of an NSAP declares which national or international
group owns the right to manage an NSAP space. This group is called an
authority. Examples of authorities that presently manage NSAP spaces
are AFNOR, ANSI and NIST. They have been given, by ISO, specific IDP
values that they control and have the right to use for the distribution of
NSAP addresses. As an example, NIST has been given the IDP value
470005 for use within the U.S. GOSIP networks. Therefore, any NSAP
AFI
IDI
IDP
DSP
19
(maximum)
Octet 0