In the FTTB/C scenario, the ONU is connected to the phone as an AG device, and no sound failure when the SIP protocol is picked up. The possible cause is:

In the FTTB/C scenario, the ONU is connected to the phone as an AG device, and no sound failure when the SIP protocol is picked up. The possible cause is:
A . olt upper network has packet loss
B . The status of the MG interface on the ONU side is abnormal
C . Voice server failure
D . The route between ONU and IMS is unreachable

Answer: B