Which statement is true about the distributed call control in a VoIP network？（）

A、A.the VoIP endpoints have the intelligence to set up and control calls

B、B.Call setup and control functionality is centralized in one call agent or cluster

C、C.Call setup and control resides in call agents that are distributed throughout the network

D、D.Each VoIP device has separate call control， voice packetization， and transport mechanisms