Power over Ethernet (PoE) powers more than one million end devices today. To continue PoE’s success, the IEEE is answering the market’s demands for more power by developing 802.3bt the third generation of PoE.
The first generation of PoE (2003), 802.3af delivered 12.95 Watts. The second generation, 802.3at (2009) provides 25.5 Watts to the equipment. The new version of PoE will address the need for higher-power PoE. The IEEE has proposed a new standard, 802.3bt, which promises to double the power output of the current 802.3at standard. The new 802.3bt standard, scheduled to be released in 2017, will also adjust PoE to work with 10Gbase-T.
Cabling Installation & Maintenance Magazine provides an excellent overview of the new standard. They report that the IEEE 802 LAN/MAN Standards Committee which develops and maintains networking standards like Ethernet, VLANs, and Wireless LAN, is developing the new standard. The DTE Power via MDI over 4-Pair Task Force is working to specify a set of next-generation PoE specifications, and the levels of power likely to be delivered ultimately via the 802.3bt standard will still work on twisted-pair cable, possibly as a four-pair PoE specification which could improve energy efficiency and offer greater power.
New POE Applications
| Industry | Application | Typical Power Consumption |
|---|---|---|
| Healthcare | Nurse call system | 30-50W |
| Retail | Point of sale system | 30-60W |
| Banking | IP Turrets | 45W |
| Building Management | Variable air volume controllers, Access controllers | 40-50W |
| Enterprise IT | Thin clients, Virtual desktop terminals | 50W |
| Hospitality | POE switches | 45-60W |
| Premise Security | PTZ cameras | 30-60W |
| Industrial | Brushless drives, Motor control | >30W |
| Various | Digital signage | >30W |
| Various | Multichannel wireless access points | >30W |
The new PoE standard will support 10GBase-T. The 10GBase-T standard uses all 4 pairs to send data. These facts will force the IEEE 802.3bt committee to figure out how to keep the power from interfering with the data on the same wires to supply a minimum of 49 watts at the powered device. One of the key parameters the article mentions is to limit pair-to-pair current imbalance.
Other goals for the 802.3bt standard are: to be backward-compatible with “af” and “at.” and increased energy efficiency. According to the article, a global move to 4-pair POE systems would create potential energy savings of 60.8 million kilowatt-hours which would prevent greenhouse gasses from 66 million pounds of coal saved annually.
Paul Vanderlaan, technical manager of cable maker Berk-Tek – Nexans’ advanced design and applications lab and other cabling-industry technical experts believe that 802.3bt’s support of 10GBase-T means that the minimum twisted-pair cabling system requirement will increase. In order to support 10GBase-T, it seems likely that a Category 6A system will be the recommendation. The author notes that the IEEE does not address cabling performance, that is the focus of groups like the TIA or ISO/IEC.
The transition to the new PoE standard will not be simple. CommScope published a white paper where they explain:
… Category 5e cabling only provides the minimum level of performance required. Therefore, it is recommended to use Category 6 or Category 6A cabling-preferably solutions …
Berk-Tek’s Vanderlaan explained why Category 6A cabling is the preferred system. He summarizes the electrical-engineering calculations;
As a general rule, increased copper content, or larger gauge size, will aid in power delivery … when you migrate … you should see larger gauge sizes and more copper content.
Under the new standard users will have to pay attention to new cabling-system performance characteristics like DC resistance unbalance and pair-to-pair resistance imbalance. The higher wattage’s up to 1 full amp (1,00 milliamps) will present challenges to performance requirements. Mr. Vanderlaan told Cabling Installation & Maintenance Magazine:
For users, cable selection will be based not just on the speed that can be supported, but rather on speed as well as power delivery. What you simply plug in today, you may want to also power in the future.
A new challenge cable plant owners will have to consider is heat. CommScope explains that heat generated within bundles of cables supporting IEEE 802.3bt could rise enough to effect performance.
… the temperature of the cabling will rise due to heat generation in the copper conductors … the temperature of the cable bundle higher than the ambient temperature of the surrounding environment … The IEEE 802.3bt four-pair PoE standard is expected to assume a maximum temperature rise of 10 degrees Celsius (50 degrees F) when all four pairs are energized … the ambient temperature should not exceed 50 degrees Celsius (122 degrees F) … CommScope recommends Category 6A cabling for four-pair PoE applications. Because increased thermal loading can also increase insertion loss, the maximum cable length should be de-rated for higher temperatures, per ANSI/TIA-568-C.2.
Several vendors have already released pre-standard device-powering systems to meet users’ current needs.
As in the pre-PoE standard days, Cisco (CSCO) has marketed proprietary PoE systems since 2011. Cisco’s Universal Power Over Ethernet (UPOE) technology, which delivers 60 watts of power to devices powered by the Catalyst 4500E; some of those devices include Cisco IP phones, personal telepresence systems, compact switches and wireless access points.
Also, the non-standard Power Over HDBase-T (POH) was introduced by the HDBase-T Alliance a trade group that promotes and standardizes HDBase-T technology for whole-home distribution of uncompressed high-definition (HD) multimedia content. This system delivers up to 100 watts of power to TVs and other devices over distances up to 100 meters/320 feet via one Category 5e or 6 cable with standard RJ45 connectors.
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The new standard is a welcome addition to the toolkit. Cost savings is one of the appeals to PoE. On many projects, PoE low voltage contractors can do the work rather than electrical contractors. If the new system pushes the maximum rate to 75W at the devices as some predict, with there be a backlash from the EC’s and authorities having jurisdiction? Time will tell.
In the meantime, the article says owners and managers should check their current infrastructure with eyes toward how the next generation of devices might be powered via more-capable PoE technology.
Of course, it is always a good idea to pull out your acceptance documentation to understand the installed base of the cable and the likelihood that the cable has the electrical performance characteristics required to support the next generation of PoE.
Related articles
- BLOG: InterDigital reveals that, like Qualcomm, it is reworking relationship with IEEE after introduction of new patent policy (iam-media.com)
Ralph Bach has been in IT long enough to know better and has blogged from his Bach Seat about IT, careers, and anything else that catches his attention since 2005. You can follow him on LinkedIn, Facebook, and Twitter. Email the Bach Seat here.
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