L2TP
Layer 2 Tunneling Protocol
L2TP is a session-layer protocol that extends the PPP model by allowing L2 and PPP endpoints to reside on different devices that are interconnected by a PSN. L2TP extends the PPP sessions between the CPE and PPP/L2TP termination point (LNS), via an intermediate L2TP access concentrator. See also LNS and LAC .