IBM SC30-3865-04 - Manual (Page 315)

Chapter 9. Using OSI/DECnet V
This chapter describes the router’s implementation of the International Standards
Organization’s (ISO) Open Systems Interconnection (OSI) Connectionless Network
Layer. DECnet Phase V supports OSI (hereafter called DECnet V/OSI) and users of
DNA V networks can use this chapter for information about the ISO OSI protocols.
This chapter contains the following sections:
v “OSI Overview”
v “NSAP Addressing” on page 286
v “Multicast Addresses” on page 288
v “OSI Routing” on page 289
v “IS-IS Protocol” on page 289
v “ESIS Protocol” on page 299
v “X.25 Circuits for DECnet V/OSI” on page 299
v “OSI/DECnet V Configuration” on page 301
v “Accessing the OSI Configuration Environment” on page 305
v “DECnet V/OSI Configuration Commands” on page 305
OSI Overview
An OSI network consists of interconnected subnetworks. A subnetwork consists of
connected hosts referred to as end systems (ESs) and routers referred to as
intermediate systems (ISs), as shown in Figure 20.
ESs contain all the layers of the OSI reference model and contain the host
applications. ISs perform the functions of the lower three layers of the OSI
reference model and handle the routing of the network protocol data units (NPDUs)
between subnetworks. ISs logically attach to the subnetwork at the subnetwork
point of attachment (SNPA). The SNPA is the access point into the data link layer.
ES
ES
Adjacent ES
Subnetwork Subnetwork Subnetwork
Adjacent IS
Adjacent
ES
SNPA
IS_1
IS_2
ES
ES
ES
ES
SNPA
Figure 20. OSI Network
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