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?（）
- AClient-based software, such as CiscoSoftPhone
- BVoice gateways, such as the Cisco VG248 Analog Phone Gateway
- CCall-management hardware and software, such as CiscoCallManager
- DAdvanced call-handling software, such as Cisco Unity