technology. Using L2TP tunneling, an ISP can create a virtual tunnel to link customers' remote
sites and remote users with corporate home networks. At the ISP, there is a device called a Local
Access Concentrator (LAC). The LAC exchanges Point-to-Point Protocol messages with
remote users and communicates by way of L2TP requests and responses with the customers'
L2TP network server (LNS) to establish the tunnels.
tunneled through L2TP tunnels.
network (PSTN), as shown in Figure 15-18. The LAC need only implement media for operation
over L2TP. A LAC can connect to the LNS using a local-area network or wide-area network,
such as public or private Frame Relay. The LAC is the initiator of incoming calls and the
receiver of outgoing calls.