Avaya Configuring XNS Services Manual do Utilizador descarregar pdf (Página 19)

XNS Overview

308651-14.00 Rev 00

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.

Protocol Layer/Level Support

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

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

3 and 4 do not involve routing, and are beyond the scope of this document.

Level 0

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

points. The Nortel 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 Manual do Utilizador Página 19