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?（）
- AAdvanced call-handling software, such as Cisco Unity
- BCall-management hardware and software, such as CiscoCallManager
- CClient-based software, such as CiscoSoftPhone
- DVoice gateways, such as the Cisco VG248 Analog Phone Gateway