7-30
ADSL WAN Connections
PPPoE Overview
Figure 7-8. Access Concentrator for PPPoE Access
Two Phases for Establishing a PPPoE Session
To establish a PPPoE session, the client and the access concentrator must
successfully complete two phases:
■ discovery phase
■ PPP session
Discovery Phase
During the discovery phase, the PPPoE client must find an access concentra-
tor, obtain the access concentrator’s Ethernet MAC address, and learn the
session ID that the access concentrator assigns this PPPoE session. If the
PPPoE client fails to obtain any of this information, the discovery phase fails,
and the PPPoE session is not established.
The PPPoE discovery phase includes four steps, as shown in Figure 7-9.
Central OfficeCustomer’s Premises
Router
DSLAM
Local
loop
Splitter
Regional
broadband
network
Splitter
LAN
Broadband
switch (ATM)
Access
concentrator
Other
DSLAMs
Negotiates PPPoE
session with router
Negotiates PPPoE session
with access concentrator
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