“The AToM framework and transport options for the various Layer 2 protocols are defined in RFC 4447, RFC 4385, RFC 4448, RFC 4717, RFC 4618, and RFC 4619. In addition to these methods to transport Layer 2 protocols, RFC 4553 and RFC 4842 define methods to transport TDM-based services, such as T1/E1, T3/E3, and SONET/SDH, over a core MPLS network.” -Tiso, John (2011-10-31). Designing Cisco Network Service Architectures (ARCH) Foundation Learning Guide: (CCDP ARCH 642-874) (3rd Edition) (Foundation Learning Guides) (Kindle Locations 4189-4191). Pearson Education. Kindle Edition.
Cisco Systems, Inc. MPLS Layer 2 VPNs—AToM at http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/ngmaneover.html#wp1058927