Any Transport over MPLS (AToM) is the Cisco solution for transporting Layer 2 traffic over an IP or MPLS backbone. AToM extends the usability of the IP/MPLS backbone by enabling it to offer both Layer 2 and Layer 3 services. The AToM product set accommodates many types of Layer 2 frames, including Ethernet, Frame Relay, ATM, PPP and HDLC, across various Cisco router platforms, such as the Cisco 12000 Series routers and the Cisco 7600, 7500, and 7200 routers.
This URl should help you:
http://www.cisco.com/en/US/netsol/ns675/networking_solutions_white_paper09186a008009d4d7.shtml
