which three commands must be configured in the MGCP fallback router?

To preserve analog calls in an MGCP switchback event, which three commands must be configured in the MGCP fallback router? (Choose Three)

A.
h323

B.
mgcp-switchback-graceful

C.
voice service voip

D.
mgcp-graceful

E.
preserve-h323

F.
no h225 timeoutkeepalive

Explanation:
Ok, 2-47

h323 : Enables H.323 voice service configuration commands
mgcp-switchback-graceful : Wrong
voice service voip : Enters voice-service configuration mode and specifies the voice encapsulation type
mgcp-graceful : Wrong
preserve-h323 :
no h225 timeout keepalive : "call preserve" and "no h225 timeout keepalive" are both used for the same general purpose, which is to preserve a call when the call processor goes down. h225 is limited however to only keep TDM-IP calls active. This means that all IP-IP calls will be dropped, regardless if the h225 command is used, whereas the IP-IP calls would be preserved if you used call preserve

h225 timeout keepalive
To disconnect H.323 calls when a TCP keepalive timeout occurs, use the h225 timeout keepalive command in H.323 voice-service configuration mode. To enable H.323 calls to remain active and ignore the TCP keepalive timeout, use the no form of this command.

h225 timeout keepalive
no h225 timeout keepalive

Router(config)# voice service voip
Router(conf-voi-serv)# h323
Router(conf-serv-h323)# no h225 timeout keepalive