which of the these can cause this issue?

The Cisco Telepresence Codec C90 is unable to call the Cisco IP Video Phone. Assuming that the
calling search space has been configured correctly, which of the these can cause this issue?

A.
The Cisco Telepresence Codec C90 can only be registered to a Cisco Telepresence Video
Communication Server.

B.
A multipoint control unit is required in order for the call to work.

C.
The Cisco Telepresence Codec C90 can only be registered as a SIP endpoint to Cisco Unified
Communications Manager. H.323 is not supported.

D.
URI dialing has not been configured on Cisco Unified Communications Manager.

E.
The Cisco Telepresence Codec C90 Profile 1 > CallSetupMode must be configured as a
gateway since Cisco Unified Communications Manager does not have a gatekeeper functionality.

F.
The Cisco Telepresence Codec C90 is not registered as a SIP endpoint on Cisco Unified
Communications Manager. The Cisco Telepresence Codec C90 needs to be registered as both
SIP and H.323.