ZyXEL Communications VMG9827-B50A User Manual page 88

Chapter 6 Broadband
WAN interface and then formatted so that they can be understood in a bridged environment. For
instance, it encapsulates routed Ethernet frames into bridged Ethernet cells.
PPP over ATM (PPPoA)
PPPoA stands for Point to Point Protocol over ATM Adaptation Layer 5 (AAL5). A PPPoA connection
functions like a dial-up Internet connection. The VMG encapsulates the PPP session based on RFC1483
and sends it through an ATM PVC (Permanent Virtual Circuit) to the Internet Service Provider's (ISP)
DSLAM (digital access multiplexer). Please refer to RFC 2364 for more information on PPPoA. Refer to RFC
1661 for more information on PPP.
PPP over Ethernet (PPPoE)
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, and so on)
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 VMG (rather than individual computers), the computers on the
LAN do not need PPPoE software installed, since the VMG does that part of the task. Furthermore, with
NAT, all of the LANs' computers will have access.
RFC 1483
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.
Multiplexing
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
VMG4927-B50A / VMG9827-B50A / VMG3927-B50B User's Guide
88