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Chapter 1
Broadband Aggregation and Leased-Line Overview
L2TP Access Concentrator Architecture
Figure 1-7
Figure 1-7
Subscribers
CPE
In the figure, wholesale providers tunnel subscriber PPP sessions to the retail provider. PPP in
L2TP sessions are encapsulated in IP packets and forwarded over any IP transport network.
Routed Bridge Encapsulation Architectures
Figure 1-8
OL-2226-23
shows an L2TP access concentrator (LAC) model.
LAC Topology
Access network
(ATM or Ethernet)
PPPoA PPPoE
over ATM PPPoE
natively on
Ethernet/802.1q
shows a routed bridge encapsulation (RBE) model.
Wholesale
provider
LAC
IP transport
network
PPP in L2TP sessions,
encapsulated in IP
Cisco 10000 Series Router Software Configuration Guide
Broadband Architecture Models
Retail
providers
LNS
provider 1
LNS
provider 2
LNS
provider n
Typically 1
tunnel per LAC
per retail provider
1-7
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Troubleshooting
