A customer with a dedicated Frame Relay network plans to move its circuits onto a service provider converged MPLS network. Instead of moving to Ethernet access links right away, the customer wants to

AToM with a control word is specifically designed to transport Layer 2 QoS information across the pseudowire; stating it is dropped contradicts the purpose of the control word mechanism.

While the Frame Relay frame including its header is encapsulated into the pseudowire payload, QoS bits are not simply carried passively in that header - they are specifically mapped into the control word for proper handling at the MPLS layer.

AToM pseudowires use an optional 4-byte control word inserted between the MPLS label stack and the Layer 2 payload to carry protocol-specific fields that have no direct mapping in MPLS. For Frame Relay, the DE (Discard Eligible) bit and congestion notification bits (FECN/BECN) are encoded into the control word fields, preserving QoS semantics end-to-end across the MPLS network. This allows the egress PE to reconstruct the original Frame Relay QoS intent on the far side of the pseudowire.

Frame Relay traffic tunneled via AToM is encapsulated in MPLS, not Ethernet, so translation to Ethernet ToS bits does not occur in this pseudowire model.