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OSI Overview

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Figure 1-7. NSAP Area Address

When a router receives a packet, it examines the contents of the packet’s NSAP

destination area address fields. The router compares its own NSAP area addresses

with the NSAP destination address contained in the packet’s header. If they match,

then the destination system is in that router’s area. If the addresses do not match,

then the destination system is located in a different area and the router must route

the packet outside the local area, using L2 routing services.

Allocating NSAP Addresses

To demonstrate how NSAP addresses are allocated, Figure 1-8

shows a sample

OSI network set up on a college campus in the United States. To obtain and

allocate NSAP addresses for the OSI network, the network administrator did the

following:

Divided the campus OSI network into areas

The administrator divided the campus OSI network into areas A, B, and C.

These three areas make up the campus routing domain.

DFIIDIAFI

AAI

ORG

Rsvd RDI Area ID S

Area Address

OSI0008A

AFI Authority and Format Identifier

IDI Initial Domain Identifier

DFI Domain Format Identifier

AAI Administrative Authority Identifier

Rsvd Reserved

RDI Routing Domain Identifier

Area Area Identifier

ID System Identifier

S NSAP Selector

IDP Initial Domain Part

DSP Domain Specific Part

Key

ORG Organization Identifier

DSPIDP

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Avaya Configuring OSI Services Manual de usuario Pagina 31