PPPoE Interfaces

The PPPoE interface to the access concentrator can be either a Fast Ethernet interface on any Services Router or an ATM-for-ADSL interface on a J4300 or J6300 Services Router. The PPPoE configuration is the same for both interfaces. The only difference is the encapsulation for the underlying interface to the access concentrator:

• If the interface is Fast Ethernet, use a PPPoE encapsulation.
• If the interface is ATM for ADSL, use a PPPoE over ATM encapsulation.

Fast Ethernet Interface

The Services Router encapsulates each PPP frame in an Ethernet frame and transports the frames over an Ethernet loop. Figure 17 shows a typical PPPoE session between a Services Router and an access concentrator on the Ethernet loop.

ATM-for-ADSL Interface

When an ATM network is configured with a point-to-point connection, PPPoE can use ATM Adaptation Layer 5 (AAL5) for framing PPPoE-encapsulated packets. The AAL5 protocol provides a virtual connection between the client and the server within the same network. The Services Router encapsulates each PPPoE frame in an ATM frame and transports each frame over an ADSL loop and a digital subscriber line access multiplexer (DSLAM). Figure 18 shows a typical PPPoE over ATM session between a Services Router and an access concentrator on an ADSL loop.