Avaya Configuring XNS Services Manuel d'utilisateur télécharger pdf (Page 22)

Configuring XNS Services

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114055 Rev. A

XNS Protocol Stack

XNS was developed at the Xerox Palo Alto Research Center (PARC). Its layered

architecture is a predecessor of the OSI architectural model. Both architectures are

functionally similar. F

igure 1-1 compares the OSI and XNS protocol stacks.

Figure 1-1. Comparison of OSI and XNS Protocol Stacks

A description of each XNS level follows:

• Level 0 protocols handle the physical transmission of data between two

points. Level 0 protocols are independent of XNS speciﬁcations. Instead, they

depend on the transmission medium available between the two points engaged

in communication. Examples of Level 0 protocols are Ethernet and Token

Ring. Level 0 corresponds generally to Layers 1 and 2, the physical and data

link layers, of the OSI model.

• The Level 1 protocol, Internet Datagram Protocol (IDP), determines where

each internet packet goes, addresses the source and destination of each

internet packet, and selects the transmission medium. Level 1 corresponds

generally to Layer 3, the network layer, of the OSI model.

Layer 7 - Application

Layer 6 - Presentation

Layer 5 - Session

Layer 4 - Transport

Layer 3 - Network

Layer 2 - Data Link

Layer 1 - Physical

Level 4 - Application

Level 3 - Control,

Process Interaction

Level 2 - Transport

Level 1 - IDP

Level 0 - Transmission

Media Protocols

OSI XNS

XNS0001A

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Avaya Configuring XNS Services Manuel d'utilisateur Page 22