Two solutions are available for transporting Layer 2 frames across a packet-switched network (PSN):
Carry the traffic across an MPLS backbone, which is the AToM solution.
Carry the traffic across an IP backbone, which is the Layer 2 Tunneling Protocol version 3 (L2TPv3) solution.
Both solutions are implemented in Cisco IOS, but because this book focuses on MPLS, only the AToM solution is explained here.
L2TPv3 is the Layer 2 transport service over an IP network. The Layer 2 frames are encapsulated with an L2TPv3 header and are transported across the IP network. Similar to AToM, L2TPv3 can carry ATM, Frame Relay, HDLC, PPP, Ethernet, ATM, and others.
Both the AToM and L2TPv3 solutions use the same architecture, ...