Transmission on the Wide Area Network

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 connection called a Permanent Virtual Circuit (PVC). Quality of Service provides UBR.

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. 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 400F, 500L, 600F, and 700F has 32 VCs in the VP, which provides the 32 sessions.

Mapping an ATM Session

Your service provider will give you a VCI and VPI address for each session. The VCI address for each session (each session is a VC) can be a number from 32 up to a maximum of 255, with the first 32 numbers (0 through 31) reserved. The VCI value for each VC must be unique for each of the 32 sessions. The VPI value must always be 0.

86

Megabit Modem 400F, 500L, 600F, and 700F User Manual