Installing and Administering OSI Transport Services

Chapter 1 51
HP OTS/9000 Resources
Structure of NSAP Addresses
Area - An area is a group of end systems and intermediate systems
interconnected by one or more subnetworks. They have been grouped
together by way of an autonomous routing mechanism. An autonomous
routing mechanism is either a set of statically configured intermediate
systems, or a set of intermediate systems that support a dynamic routing
protocol, such as the ISO IS-IS protocol.
Routing Domain - A Routing Domain is also a group of end systems
and intermediate systems interconnected by one or more subnetworks.
They have been grouped together by way of some routing or security
policy defined by the network administrator. Typically, a number of areas
are grouped together to form a routing domain.
An area may be composed of one or more subnetworks. The criteria for
grouping subnetworks into areas can be based upon topology,
reachability, and network traffic. The criteria for grouping areas into
routing domains is based upon policy. For instance, a company might
want to create an area for their factory, and area for their product design
lab and put them in the same routing domain. However, the company
may choose to create a separate routing domain for their accounting and
payroll departments.
To facilitate routing strategy, a network administrator will often define
the PAP to contain one or more of the following fields:
• Routing Domain Identifier
• Area Identifier
• Subnetwork Identifier
• End System Identifier
The order they are listed here is the order, left to right, in which they
would be defined in a PAP.
Other fields that often find their way into the PAP are:
Version Number or DSP Format Identifier - The purpose of these
fields is to allow a network administrator to redefine the PAP structure
at a later point in time, or allow the network administrator to define
several PAP formats. Each format would be identified by a different
value in the Version Number or DSP Format Identifier field.