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

• A、Advanced call-handling software, such as Cisco Unity
• B、Call-management hardware and software, such as CiscoCallManager
• C、Client-based software, such as CiscoSoftPhone
• D、Voice gateways, such as the Cisco VG248 Analog Phone Gateway