Which three events describe the relationship of an IP phone to its secondary subscriber in a Cisco Unified Communications Manager system? (Choose three.)
A.
The IP Phone sends a TCP keepalive message every 30 seconds.
B.
The IP Phone registers with all the Cisco Cisco Unified Communications Manager subscribers in the group simultaneously, including the secondary subscriber.
C.
The IP Phone sends a TCP connect message.
D.
The IP Phone registers with the primary system when the secondary system is unavailable.
E.
The IP Phone sends a TCP keepalive message every 60 seconds.
F.
The IP Phone attempts to register with the secondary system when the primary system is unavailable.