Installing and Administering OSI Transport Services

64 Chapter 1
HP OTS/9000 Resources
A Recommended PAP Structure
The above PAP allocation follows the structure used by the IS-IS
protocol. It allows areas to be created that contain multiple subnetworks.
The User Defined portion may be comprised of one or more of the
following fields:
• A version or DSP format identifier. This allows the format of the PAP
to be redefined at some later point in time. These fields are usually
two octets in length, but any size may be chosen. For most NSAP
spaces, one octet will often be sufficient.
• A reserved field. It is often a good idea to reserve a few octets of space
for future use.
If any of these fields are used, they should be defined in the order, left to
right in the PAP, as they are listed above.
Network Identifiers (Network ID)
Because of the hierarchical definition of NSAP formats, a prefix portion
of an NSAP may be used to identify a group of systems that reside in the
same routing domain, the same area, or the same subnetwork. This
prefix portion is called an “NSAP Prefix,” or a “Network ID.”
As an example, suppose Joe’s Grommet Shop, whose AP value is
39840F010101, decides to use the Recommendation 1 format for its PAP.
Figure 1-24
It has two areas in routing domain 0000 that are assigned Area ID
values: 0001 and 0002. The corresponding Network IDs for these areas
are: 39840F01010100000001 and 39840F01010100000002.
Network IDs may be used in OTS to simplify the configuration of routing
information. Rather than configuring a route to every remote system,
OTS allows network administrators to configure a route to a distant
routing domain, area, or subnetwork by using its Network ID. It also
allows local subnetworks to have their Network IDs configured to help
the routing protocols with local network traffic.
39840F010101
AP
PAP
length (octets) 6
Domain Area
ES ID 01
22 1
IDID