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I'm getting a little confused on how PPPoE works at the "layer 2" level. If a PPPoE is a ppp frame encapsulated within an ethernet frame and it is being transmitted over an ATM network, then is the packet theoretically being encapsulated in 3 frames/protocols. Is the packet encapsulated within a PPP frame, then encapsulated in an Ethernet frame and then again encapsulated in a ATM cell to be transported across the ATM network? If this is correct, where is this happening in the DSL infrastructure? Does all this happen at the DSL modem, or is the Ethernet frame (with the PPP frame inside)transmitted from the DSL modem to the DSLAM where it is then either encapsulated again in a ATM cell or is the ethernet frame stripped off and the ATM cell is applied. I'll be honest...I dont know much about ATM, but I have read a little about it and cant make that connection with DSL PPPoE.



well, yes, the data is encapsulated multiple times as you've described.

the ethernet frame is constructed by the NIC of the system putting it onto the wire.

once that frame gets to the ADSL router, it is encapsulated in a PPP packet and then put onto the ATM network in a cell.

(from the cpe, your 857, all the way through the ISP DSLAM, PPPoE/A is used, where at that point the DSL signals are split in two for voice and data)

please see the following link for some more info on ATM operation: