When analog signals are digitized using the G.711 codec， voice samples are encapsulated into protocol data units （PDUs） involving which three headers？ （）

A.the VoIP endpoints have the intelligence to set up and control calls
B.Call setup and control functionality is centralized in one call agent or cluster
C.Call setup and control resides in call agents that are distributed throughout the network
D.Each VoIP device has separate call control， voice packetization， and transport mechanisms

A.to build a Packet Description Language Module （PDLM） file to be used in protocol matching
B.to discover applications and build class maps for data classification
C.to look into the TCP or UDP payload and classify packets based on the content
D.to build a database of all application data that passes through the router and queue the data accordingly

A.Gatekeeper multizone
B.Call Admission Control （CAC）
C.Automatic Alternate Routing （AAR）
D.Survivable Remote Site Telephony （SRST）
E.Cisco Unified CallManager Express （CME）