Power over Ethernet (PoE) is the ability for the LAN switching infrastructure to provide power over a copper Ethernet cable to an endpoint (Powered Device). This capability, once referred to as "inline power", was originally developed and first delivered by Cisco in 2000 to support the emerging IP Telephony deployments. IP Telephones, like desktop PBX phones, need power for their operation and Power over Ethernet enables scalable and manageable power delivery and simplifies deployments of IP Telephony. As Wireless networking emerged, Power over Ethernet was also used to power these devices to allow for deployments in locations where local power access did not exist. While IP telephones and wireless access points are the most intuitive uses for PoE, the advent of 802.3af standardization of PoE opens the door to a new generation of networked-attached devices such as video cameras, point-of-sale devices, security access control (card scanners), building automation and industrial automation just to name a few. When a Cisco switch supply PoE to an IP phone?

A.
whenever switch and IP phone are Cisco products.

B.
when Cisco switch supports prestandard PoE and the IP phone supports 802.3af.

C.
when Cisco switch and IP phone both support a common PoE method.

D.
Only when both the switch and IP phone use 802.3af PoE.