Which IP telephony component provides call processing, such as signaling that in traditional voice network is provided by switching equipment, such a PBX?

A.
client-based software, such as Cisco SoftPhone

B.
voice gateways, such as the Cisco VG248 Analog Phone Gateway

C.
call-management hardware and software, such as Cisco CallManager

D.
advanced call-handling software, such as Cisco Unity