Which statements about MPLS Label Distribution Protocol（LDP） are valid？（）

A.LDP hello packets are sent to UDP port 646

B.LDP hello packets are sent to TCP port 711

C.LDP sessions are TCP sessions to port 646

D.LDP sessions are TCP sessions to port 711

E.LDP establishes a peer relationship with another router that must be directly attached

F.LDP can establishes a peer relationship with another router that is not directly attached