ZyXEL Communications Prestige 662HW Series, Руководство пользователя

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Prestige 662HW Series User’s Guide
PPPoE C-1
Appenidx C
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) that 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 and 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 C-1 Single-PC per Router 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.
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.