Which two statements about the Diameter message direction on the Rf interface are true? (Choose two.)
A. Diameter Accounting-Request is initiated by S-GW/P-GW to CDF.
B. Diameter Accounting-Answer is initiated by CDF to S-GW/P-GW.
C. Diameter Accounting-Request is initiated by S-GW/P-GW to CGF.
D. Diameter Accounting-Answer is initiated by CGF to S-GW/P-GW.
E. Diameter Accounting-Request is initiated by S-GW/P-GW to the billing server.
F. Diameter Accounting-Answer is initiated by the billing server to S-GW/P-GW.