Avaya Configuring XNS Services Manuel d'utilisateur télécharger pdf (Page 19)

XNS Overview

1-3

• Level 2 protocols provide for the exchange of routing information between

routers, handle the sequencing of packets within a packet stream, report

transmission errors, retransmit packets in response to errors, suppress

duplicate packets, and adjust the rate of packet transmission (ﬂow control).

Examples of Level 2 protocols are Routing Information Protocol, Error

Protocol, Echo Protocol, Sequenced Packet Protocol, and the Packet

Exchange Protocol. Level 2 corresponds to Layer 4, the transport layer, of the

OSI model.

• Level 3 protocols are control protocols; they determine process interactions

that involve remote resources, such as printer and ﬁle requests, and data

structuring conventions. Level 3 corresponds generally to Layers 5 and 6, the

session and presentation layers, of the OSI model.

• Level 4 protocols are application protocols that are implemented for speciﬁc

platforms. Level 4 corresponds to Layer 7, the application layer, of the OSI

model.

The following sections describe the involvement of the Bay Networks XNS

routing software in Levels 0, 1, and 2. Levels 3 and 4 do not involve routing, and

are beyond the scope of this document.

Protocol Layer/Level Support

This section describes in detail the protocol support that Bay Networks XNS

routing software provides at Level 0, 1, and 2 of the XNS protocol model.

Level 0

The XNS Level 0 protocols handle the physical transmission of data between two

points. The Bay Networks router running XNS software supports the following

Level 0 protocols or frame formats/encapsulations:

• Ethernet: Ethernet II

• Token Ring: SNAP

• FDDI: SNAP

• Frame Relay: Frame Relay SNAP

• SMDS: SMDS SNAP

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Avaya Configuring XNS Services Manuel d'utilisateur Page 19