249Nortel Business Secure Router 222 Configuration — AdvancedAppendix DPPPoEPPPoE in actionAn ADSL modem bridges a PPP session over Ethernet (PPP over Ethernet, RFC2516) from your PC to an ATM PVC (Permanent Virtual Circuit), which connectsto a DSL Access Concentrator where the PPP session terminates (see Figure 155).One PVC can support any number of PPP sessions from your LAN. PPPoEprovides access control and billing functionality in a manner similar to dial-upservices using PPP.Benefits of PPPoEPPPoE offers the following benefits:• It provides you with a familiar dial-up networking (DUN) user interface.• It lessens the burden on the carriers of provisioning virtual circuits all the wayto the ISP on multiple switches for thousands of users. For GSTN (PSTN andISDN), the switching fabric is already in place.• It allows the ISP to use the existing dial-up model to authenticate and(optionally) to provide differentiated services.Traditional dial-up scenarioFigure 155 depicts a typical hardware configuration where the PCs use traditionaldial-up networking.
