MPLS L2VPN - Any Transport over MPLS (AToM) by Arash Deljoo

Any Transport over MPLS (AToM) accommodates different types of Layer 2 packets, including Ethernet and VLAN, to enable the service provider to transport different types of traffic over the backbone and accommodate all types of customers. 

AToM adheres to the standards developed for transporting Layer 2 packets over MPLS. Other Layer 2 solutions are proprietary, which can limit the service provider’s ability to expand the network and can force the service provider to use only one vendor’s equipment.

Upgrading to AToM is transparent to the customer. Because the service provider network is separate from the customer network, the service provider can upgrade to AToM without disruption of service to the customer.

The successful transmission of the Layer 2 frames between PE devices is due to the configuration of the PE devices. You can set up the connection, called a pseudo wire, between the routers and specify the following information on each PE device:

• The type of Layer 2 data to be transported across the pseudowire, such as Ethernet or VLAN.
• The IP address of the loopback interface of the peer PE device, which enables PE devices to communicate.
• A unique combination of peer PE IP address and virtual circuit (VC) ID that identifies the pseudo wire.

AToM encapsulates Layer 2 frames at the ingress provider edge (PE) and sends them to a corresponding PE at the other end of a pseudo wire. The egress PE removes the encapsulation and sends out the Layer 2 frame.