802.3at pumps up Power over Ethernet

The IEEE is working to enhance the 802.3af Power over Ethernet standard with PoE plus.

The IEEE is working to enhance the 802.3af Power over Ethernet standard to give networked devices more juice. PoE provides a way to deliver electrical power over LAN cabling to networked devices, such as IP phones, wireless access points and IP security cameras.

The IEEE formed a working group to develop the 802.3at standard or PoE Plus, with the goal of boosting the amount of power that PoE can deliver.

The group is evaluating whether to continue to carry electricity on two wire pairs or move the electrical current onto all four Ethernet wire pairs. Each copper wire in a cable's bundle can take only so much power before being damaged. Likewise, the wires in an Ethernet bundle can carry only so much total wattage before the bundle overheats, creating cable life-expectancy concerns. The IEEE also must account for possible interference between higher-powered electricity and data signals. Cabling specialists are investigating what those limits are.

Once researchers determine the best delivery method, the working group will set the wattage limits. The current standard delivers as much as 15.4 watts; the goal for the new standard is to provide 30 watts or more. It's possible that PoE Plus could deliver as much as 60 watts, which is enough to power high-speed, dual-radio access points or almost any other mobile multimedia device.

As a part of the standard, PoE Plus will specify guidelines for Category 5 and higher Ethernet cable, as well as support power delivery with 10M, 100M, 1G and perhaps even 10Gbps data delivery.

In addition to boosting power, the IEEE is exploring new, improved power-management capabilities for PoE. These would make it possible for a switch to have more electricity available for more devices. The current 802.3af PoE standard delivers power at three levels: 4, 7 or 15.4 watts. PoE Plus will likely make it possible for a PoE-enabled switch to allocate exactly the amount of power a device needs and to adjust the power to the device automatically, such as when a device moves from standby to active use.

The industry must wait patiently for PoE Plus, however. Standards groups tend to move slowly, and the IEEE's 802.at working group is no exception. The most optimistic estimate for the first publication of the 802.3at standard is early 2007. If the group gets ambitious and wants to include more features into PoE Plus, it could take a bit longer, leaving the networking industry without the much-needed power boost. Either way, it is likely to be well into 2007 or 2008 before there is a ratified standard.

PoE Plus will be worth the wait, however. The higher wattage will address the burgeoning use of such devices as dual-radio wireless network access points and motorized cameras, which typically require more than the current PoE limit.

Originally built to simplify VoIP deployments, PoE has become crucial to lowering the costs of building wireless networks and has inspired a host of new devices, including networked video cameras and even an Ethernet-enabled electric guitar.

With the higher wattage and greater power management of PoE Plus, a new generation of devices will benefit organizations and consumers with the convenience of plug-and-play networking.

Barrass and Schindler are engineers for Cisco Systems' desktop switching business unit. Both are members of the IEEE 802.3at task force. They can be reached at hbarrass@cisco.com and frs@cisco.com, respectively.

How it works: 802.3at

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