ZyXEL Communications Prestige 310 - Manual (Page 147)

Prestige 310 Broadband Sharing Gateway
PPPoE G
Appendix B: PPPoE
PPPoE in Action
An ADSL modem bridges a PPP session over Ethernet (PPP over Ethernet, RFC 2516) from your PC to an
ATM PVC (Permanent Virtual Circuit) which connects to a xDSL Access Concentrator where the PPP
session terminates (see the next figure). One PVC can support any number of PPP sessions from your LAN.
PPPoE provides access control and billing functionality in a manner similar to dial-up services using PPP.
Benefits of PPPoE
PPPoE offers the following benefits:
1. It provides you with a familiar dial-up networking (DUN) user interface.
2. It lessens the burden on the carriers of provisioning virtual circuits all the way to the ISP on multiple
switches for thousands of users. For GSTN (PSTN & ISDN), the switching fabric is already in place.
3. It allows the ISP to use the existing dial-up model to authenticate and (optionally) to provide
differentiated services.
Traditional Dial-up Scenario
The following diagram depicts a typical hardware configuration where the PCs use traditional dial-up
networking.
Diagram 1 Single-PC per Modem Hardware Configuration
How PPPoE Works
The PPPoE driver makes the Ethernet appear as a serial link to the PC and the PC runs PPP over it, while the
modem bridges the Ethernet frames to the Access Concentrator (AC). Between the AC and an ISP, the AC is
acting as a L2TP (Layer 2 Tunneling Protocol) LAC (L2TP Access Concentrator) and tunnels the PPP
frames to the ISP. The L2TP tunnel is capable of carrying multiple PPP sessions.