ZyXEL Communications Corporation VMG1312B10C Manual Do Utilizador

 Chapter 5 Broadband

VMG1312-B10C User’s Guide

Point-to-Point Protocol over Ethernet (PPPoE) provides access control and billing functionality in a 
manner similar to dial-up services using PPP. PPPoE is an IETF standard (RFC 2516) specifying how 
a personal computer (PC) interacts with a broadband modem (DSL, cable, wireless, etc.) 
connection. 

For the service provider, PPPoE offers an access and authentication method that works with existing 
access control systems (for example RADIUS).

One of the benefits of PPPoE is the ability to let you access one of multiple network services, a 
function known as dynamic service selection. This enables the service provider to easily create and 
offer new IP services for individuals.

Operationally, PPPoE saves significant effort for both you and the ISP or carrier, as it requires no 
specific configuration of the broadband modem at the customer site.

By implementing PPPoE directly on the Device (rather than individual computers), the computers on 
the LAN do not need PPPoE software installed, since the Device does that part of the task. 
Furthermore, with NAT, all of the LANs’ computers will have access.

RFC 1483 describes two methods for Multiprotocol Encapsulation over ATM Adaptation Layer 5 
(AAL5). The first method allows multiplexing of multiple protocols over a single ATM virtual circuit 
(LLC-based multiplexing) and the second method assumes that each protocol is carried over a 
separate ATM virtual circuit (VC-based multiplexing). Please refer to RFC 1483 for more detailed 
information.

There are two conventions to identify what protocols the virtual circuit (VC) is carrying. Be sure to 
use the multiplexing method required by your ISP.

VC-based Multiplexing

In this case, by prior mutual agreement, each protocol is assigned to a specific virtual circuit; for 
example, VC1 carries IP, etc. VC-based multiplexing may be dominant in environments where 
dynamic creation of large numbers of ATM VCs is fast and economical.

LLC-based Multiplexing

In this case one VC carries multiple protocols with protocol identifying information being contained 
in each packet header. Despite the extra bandwidth and processing overhead, this method may be 
advantageous if it is not practical to have a separate VC for each carried protocol, for example, if 
charging heavily depends on the number of simultaneous VCs.

Traffic Shaping is an agreement between the carrier and the subscriber to regulate the average rate 
and fluctuations of data transmission over an ATM network. This agreement helps eliminate 
congestion, which is important for transmission of real time data such as audio and video 
connections.