The IEEE published its IEEE 802.3af standard in 2003. This document, known as the “PoE” standard, specifies power delivery up to 15.4 W for an Ethernet port using two pairs of Cat-5e cable. In 2009, the IEEE completed the IEEE 802.at standard, specifying power levels up to 25.5 W per port, again using two of the pairs in Cat-5e or Cat-6 cable. It is known as the “PoE+” standard.
The IEEE 802.3af standard specifies the injection of DC power at 4, 7, 15.4 W. Devices that operate at other power levels, such as 6-W IP telephones, can be operated with power sources that detect the required power level and also comply with IEEE 802.3af.
Cisco Systems, for example supplies powered devices that can communicate their power requirement to the Ethernet switch or power source. Cisco’s Ethernet switches incorporate “Intelligent Power Management” software to sense the power requirements and adjust the power level at each port to operate most efficiently.
The 15-W power level in IEEE 802.3af proved adequate for IP telephones, Wi-Fi antenna units, and fixed-lens cameras. But some devices require the higher power levels of PoE+. Examples include cameras with motors for pan, tilt, and zoom, or cameras with heating systems to prevent moisture from freezing on the lens, and new higher-power Wi-Fi standard (IEEE 802.11n). The 2009 IEEE 802.3at standard met the power requirements for many of these devices. It also allowed two devices to be powered with a single Cat-5e cable.
At the same time, it was apparent that there was interest in higher power levels. New classes of powered devices were envisioned, such as wireless-network small cells and distributed antenna systems. Several equipment companies had R&D programs to investigate higher power levels using all four pairs for power delivery.
Over the years, there also have been companies offering devices that incorporate non-standard power levels, and proprietary technologies for power over TWP cabling. Some of these have aimed to deliver higher power levels. Starting in 2014, the IEEE 802.3 Working Group began work on a standard for power levels up to 71 W using all four pairs. As of late 2017, there was a version of the new standard in draft form, with a final draft and approval expected in 2018. In a December 2017 statement, the Ethernet Alliance said final ratification is expected in September of 2018. The standard will be known as IEEE 802.3bt.
The IEEE 802.3bt standard will have two versions – two power levels. One specifies the source power maximum at 60 W, and the other will be at 90 W. This standard contains protocols for communication between the power source equipment and the powered devices, so that the source unit can adjust the injected power level to meet the powered device’s requirement.
For short distances, with minimal resistance and less power dissipation, the protocol allows for measurement of the actual cable resistance. For short distances, the power received by the powered device can be higher. Thus, the IEEE 802.3bt standard specifies the power received at the power device as a range. In the first version, the input at the powered devices will range from 51W to 60 W. In the second version, it will range from 71W to 90W. The IEEE 802.3af and IEEE 802.3at standards do not incorporate this power-range capability. The powered device’s received power therefore is less than the injected power, to allow for the power dissipation.
When the IEEE 802.3bt standard is ratified, the three IEEE standards as a group will specify four power levels. Thus, PoE is referred to as having four "types":
Part of the interest in higher PoE power levels is the potential powering of laptop and desktop PCs, video-conference equipment, and other electronics with screens and speakers. The work on power over HDBaseT cables has been motivated by interest in connecting audio, video, and multi-media equipment – both consumer and commercial products.
HDMI and HDBaseT are distinct digital transmission technologies. HDMI was introduced in 2002 for point-to-point links between HD video displays the signal-source equipment. The HDMI cables and connectors are not compatible with the LAN category cables in the TIA-568 structured cabling standard or in the IEEE 802.3 family of Ethernet standards. The HDMI technology is mainly intended for short-distance transport of high-end audio and video signals. HDMI cables are usually sold in 25-foot lengths, and area available in lengths up to 50 feet (15 meters) at most.
HDBaseT was introduced in 2010 to provide a data transmission standard supporting five functions: HDTV, audio, Ethernet, controls, and power delivery, all over single four-pair cable. The HDBaseT Alliance refers to this capability as “5Play.” The Alliance promotes the technology for applications in consumer electronics, corporate networks, industrial PCs, automotive networks, medical imaging, and other industries.
As currently supported by equipment manufacturers, the HDBaseT cable system can transport up 10.2 Gbps of uncompressed high-definition video and audio, 100BaseT Ethernet, control signals, and power in the same cable over distances of 100 meters. Recent versions of HDBaseT equipment also are capable of transporting USB2.0 and 4K video, and the technology will allow multi-stream video and higher resolution video in the future.
HDBaseT technology also supports multiple “hops” to achieve distances longer than 100 meters. There also are single-mode and multimode versions available for distancers greater than 100 meters. Single-mode versions are available for distances up to 10 km.
Some early implementations of HDBaseT systems using Cat-5e cable encountered problems with the cable’s 100-MHz bandwidth specification. Cat-6a cable, which is rated at 500 MHz, has proved successful in meeting the high frequency applications.
Power over HDBaseT (PoH) was introduced in September 2011. In a publication introducing the new standard, the HDBaseT alliance said it “is based on the IEEE 802.3at standard with the appropriate modifications to enable safe delivery of 100 W over the four pairs of an Ethernet cable.” The statement also said the standard includes detection and protection mechanisms to ensure safe and reliable power deliver.
Use of HDBaseT for in-home transport of television programs is considered a key consumer application. PoH technology has been standardized to provide the power levels required by most television sets – up to 100 W. At the same time, TV energy requirements are decreasing with improvements in display technology. PoH also is promoted for television applications because it eliminates the need for ac-to-dc converter, which some customers may consider to be cumbersome with the thinner wall-mounted sets. PoH, however also means that consumers must bear the additional cost of RJ45 interfaces and Cat-6a cabling. For low-end TV sets and video players, this cost may not be justified.
In the commercial world, PoH is generating interest for video-conferencing equipment and some PCs. Like PoE, the standard can offer energy efficiency and simplified network design and installation.