It is possible to use Frame Relay switches as Label, Switching Routers. Such Frame Relay switches run network layer routing algorithms (such as OSPF, IS-IS, etc.), and their forwarding

is based on the results of these routing algorithms. No specific

Frame Relay routing is needed.

When a Frame Relay switch is used for label switching, the top

(current) label, on which forwarding decisions are based, is carried

in the DLCI field of the Frame Relay data link layer header of a

frame. Additional information carried along with the top (current)

label, but not processed by Frame Relay switching, along with other

labels, if the packet is multiply labeled, are carried in the generic

MPLS encapsulation defined in [STACK].

Check this out.

http://www.ietf.org/rfc/rfc3034.txt