ZyXEL Communications Prestige 641, Руководство пользователя, Страница: 111 / 117

Prestige 641 ADSL Internet Access Router
E
Appendix
Appendix A
PPP over Ethernet
PPPoE (PPP over Ethernet, RFC 2516) uses Ethernet as a point-to-point link to transport PPP frames.
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
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 Tunnelling Protocol) LAC (L2TP Access Concentrator) and tunnels the
PPP frames to the ISP. The L2TP tunnel is capable of carrying multiple PPP sessions.
With PPPoE, the VC (Virtual Circuit) is equivalent to the dial-up connection and is between the modem and
the AC, as opposed to all the way to the ISP. However, the PPP negotiation is between the PC and the ISP.
ADSL Modem
ADSL Modem
ADSL Modem
ADSL Modem
ISP 1
Access Concentrator
ISP 2
ATM