Explanation/Reference:
Explanation:
http://www.cisco.com/en/US/products/ps6603/products_qanda_item09186a008009d4e3.shtml#wp39173
Q. How does Frame Relay over MPLS work?
A. Traffic is encapsulated in MPLS packets and forwarded across the MPLS network. When encapsulating Frame Relay over MPLS, the Frame Relay header and the frame check sequence (FCS) are stripped from the packet. The bits for Backward Explicit Congestion Notification (BECN), Forward Explicit Congestion Notification (FECN), Discard Eligibility (DE) and Command/Response (C/R) are carried across the MPLS network in the "Control Word" header.