Mapping an ATM Session

PPPPRELIMINARY

ATM

Asynchronous Transfer Mode (ATM) is a technology that can simultaneously transmit voice, data, and video over ADSL. ATM uses fixed-size cells that transmit over a preestablished

ATM cells are 53 bytes that comprise a 5-byte header and 48-byte payload. The header includes the Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI) that you entered when you configured each session in Chapter 4. The VPI and VCI provide the virtual connection between the modem and the service provider. The VPI identifies the Virtual Path (VP) that transports ATM cells in a Virtual Channel (VC). The Megabit Modem 500L has three VCs in the VP, which provide the three sessions for the Internet or for other WAN applications. You can, however, activate only one session at a time.

connection called a Permanent Virtual Circuit (PVC). Quality of Services can alsoRYbe specified.

with the first 32 numbers (0 through 31) reserved. The VCI value for each VC must be unique for each of the three sessions. The VPI value must always be 0.

Your service provider will give you a VCI and VPI addressNfor eachAsession. The VCI address, for each session (each session is a VC), can be a numberIup to a maximum of 255 (32 to 255),

PPP

I

 

EL

PPP runs over ATM virtual circuits. PPP exists between the hardware layer and the

network-layer interface protocols. It is aMwidely used protocol for establishing connections on

the Internet. PPP provides the set up and release of connections for each session. PAP/CHAP provide the authentication for the PPP sessions.

You can configure three sessions , but only one session can be established between the service

provider and the modem at a time. The user is mapped to the session that is active. PR

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Megabit Modem 500L Installation Manual