treated as a Class 0 device. Configuration via Ethernet layer 2 LLDP Link Layer Discovery Protocol (LLDP) is a layer-2 Ethernet protocol for managing devices. LLDP allows an exchange of information between a PSE and a PD. This information is formatted in type–length–value (TLV) format. PoE standards define TLV structures used by PSEs and PDs to signal and negotiate available power. The setup phases are as follows: PSE (provider) tests PD (consumer) physically using 802.3af phase class 3. PSE powers up PD. PD sends to PSE: I'm a PD, max power = X, max power requested = X. PSE sends to PD: I'm a PSE, max power allowed = X. PD may now use the amount of power as specified by the PSE. The rules for this power negotiation are: PD shall never request more power than physical 802.3af class PD shall never draw more than max power advertised by PSE PSE may deny any PD drawing more power than max allowed by PSE PSE shall not reduce power allocated to PD that is in use PSE may request reduced power, via conservation mode Non-standard implementations Cisco Some Cisco WLAN access points and VoIP phones supported a proprietary form of PoE many years before there was an IEEE standard for delivering PoE. Cisco's original PoE implementation is not software upgradeable to the IEEE 802.3af standard. Cisco's original PoE equipment is capable of delivering up to per port. The amount of power to be delivered is negotiated between the endpoint and the Cisco switch based on a power value that was added to the Cisco proprietary Cisco Discovery Protocol (CDP). CDP is also responsible for dynamically communicating the Voice VLAN value from the Cisco switch to the Cisco VoIP Phone. Under Cisco's pre-standard scheme, the PSE (switch) will send a fast link pulse (FLP) on the transmit pair. The PD (device) connects the transmit line to the receive line via a low-pass filter. The PSE gets the FLP in return. The PSE will provide a common mode current between pairs 1 and 2, resulting in and default of allocated power. The PD must then provide Ethernet link within to the auto-negotiation mode switch port. A later CDP message with a TLV tells the PSE its final power requirement. A discontinuation of link pulses shuts down power. In 2014, Cisco created another non-standard PoE implementation called (UPOE). UPOE can use all 4