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Chapter 6 Broadband
VMG5313-B10A/-B30A Series User’s Guide
101
IP over Ethernet
IP over Ethernet (IPoE) is an alternative to PPPoE. IP packets are being delivered across an
Ethernet network, without using PPP encapsulation. They are routed between the Ethernet interface
and the 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, 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 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