MBGP neighbor has been set up, and so does OSPF neighbor. At NE20E, executing disp mpls ldp session command finds no output. NE20E could receive the private network route from the peer.
Change the label allocation protocol of C equipment to LDP, and then NE20E could set up LDP neighbor with C equipment normally.
The protocol of C equipment to allocate label differs to the LDP of NE20E. C equipment uses its private label allocation protocol--TDP.