ZyXEL p-660h-61 用户指南

Prestige 660H Series User’s Guide 

PPPoE 

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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. 

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. 

The following diagram depicts a typical hardware configuration where the PCs use traditional dial-up 
networking.  

 

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.