Installing and Administering OSI Transport Services

50 Chapter 1
HP OTS/9000 Resources
Structure of NSAP Addresses
39840F010101. Any NSAP that begins with this value is under the
control of Joe’s Grommet Shop. Joe’s Grommet Shop may also define the
format for the rest of the DSP to suit their needs.
The fields of an NSAP create a hierarchy where each field further divides
the NSAP space into smaller, more manageable spaces. Also, the leftmost
portion of an NSAP deals with the administration of NSAP spaces, not
specifically with the identification of real systems. In the above example,
the leftmost part of the NSAP space is “publicly” administered, that is,
administered by national and international standards bodies, whereas
the right part is left up to private organizations to define and use. For
convenience, these two parts will be called the administrative prefix
(AP), and the privately allocated part (PAP).
Figure 1-10
This separation between what a network administrator is given and
what the administrator controls is very important. It is the key to
understanding how an NSAP space is managed. Also, some companies
may have several different APs, or may start with one AP and have to
migrate over to a different one at some point in time. Only through
careful management of the PAP can a network administrator minimize
the problems that this may cause.
The Privately Allocated Part
Whereas the AP is used to administer NSAP spaces, the PAP is used to
define a routing strategy. The two portions, when combined together,
yield a unique NSAP for a given system.
The ISO model of routing contains the following levels:
Subnetwork - A subnetwork is an autonomous collection of equipment
and medias used to interconnect systems. Examples of types of
subnetworks are: IEEE 802.3 LANs and X.25 PDNs.
AFI
IDI
IDP
DSP
(allocated by international
AP
DSP
and national authorities)
(privately allocated part)