available at the powered device as some power dissipates in the cable. The updated IEEE 802.3at-2009 PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power for Type 2 devices. The 2009 standard prohibits a powered device from using all four pairs for power. Both of these standards have since been incorporated into the IEEE 802.3-2012 publication. The IEEE 802.3bt-2018 standard further expands the power capabilities of 802.3at. It is also known as PoE++ or 4PPoE. The standard introduces two additional power types: up to 51 W delivered power (Type 3) and up to 71.3 W delivered power (Type 4). Each pair of twisted pairs needs to handle a current of up to 600 mA (Type 3) or 960 mA (Type 4). Additionally, support for 2.5GBASE-T, 5GBASE-T and 10GBASE-T is included. This development opens the door to new applications and expands the use of applications such as high-performance wireless access points and surveillance cameras. Single-pair Ethernet The IEEE 802.3bu-2016 amendment introduced single-pair Power over Data Lines () for the single-pair Ethernet standards 100BASE-T1 and 1000BASE-T1 intended for automotive and industrial applications. On the two-pair or four-pair standards, the same power voltage is applied to each conductor of the pair, so that within each pair there is no differential voltage other than that representing the transmitted data. With single-pair Ethernet, power is transmitted in parallel to the data. PoDL initially defined ten power classes, ranging from 0.5 to 50 W (at PD). Subsequently, PoDL was added to the single-pair variants 10BASE-T1, 2.5GBASE-T1, 5GBASE-T1, and 10GBASE-T1 and includes a total of 15 power classes with additional intermediate voltage and power levels. Uses Examples of devices powered by PoE include: VoIP phones IP cameras including PTZs WAPs IP TV (IPTV) decoders Network routers A mini network switch installed in distant rooms, to support a small cluster of Ethernet ports from one uplink cable. PoE power is fed into the PD (or PoE in) port. These switches may in turn power remote PoE devices using PoE pass through. Intercom and public address systems and hallway speaker amplifiers Wall clocks in rooms and hallways, with time set using Network Time Protocol (NTP) Outdoor roof mounted radios with integrated antennas, 4G/LTE, 802.11 or 802.16 based wireless CPEs (customer premises equipment) used by wireless ISPs Outdoor point to point microwave and millimeter wave radios and some Free Space Optics (FSO) units