The feature whereby any Layer 2 frame is carried across the MPLS backbone is called Any
Transport over MPLS (AToM). The routers that are switching the AToM traffic do not need to be
aware of the MPLS payload; they just need to be able to switch the labeled traffic by looking at
the label on top of it. In essence, MPLS label switching is a simple method of switching multiple
protocols in one network. You need to have a forwarding table consisting of incoming labels to be
swapped by outgoing labels and a next hop.
In short, AToM enables the service provider to provide the same Layer 2 service toward the
customers as with any specific non-MPLS network. At the same time, the service provider needs
only one unified network infrastructure to carry all kinds of customer traffic.