4. Signage

Before transporting PPP frames through a tunnel, the L2TP protocol must ensure two important points:

• establishment of a control connection between the LAC and the LNS, enabling management of the tunnel and sessions within it;

• setting up the transport session inside the tunnel.

Establishing the control connection is the first step in initiating one or more L2TP sessions. It corresponds to the establishment of the L2TP tunnel between the two entities, the LAC and the LNS.

An L2TP tunnel can contain several L2TP sessions; similarly, there can be several different tunnels between an LAC and an LNS.