Helping PoE reach its potential

Power-over-Ethernet is helping bring to organizations and individuals to enjoy the benefits of a wired world. But with success comes greater responsibility. Now that the Power-over-Ethernet standard, or PoE, is so widely adopted—most networking equipment vendors support PoE in some form—it's time for the standard to do more.

Power-over-Ethernet is helping bring to organizations and individuals to enjoy the benefits of a wired world. But with success comes greater responsibility. Now that the Power-over-Ethernet standard, or PoE, is so widely adopted—most networking equipment vendors support PoE in some form—it's time for the standard to do more.

Since its debut as an official standard in 2003, PoE has clearly proved its value by offering a way to deliver electricity to network devices over standard Ethernet data cables. This watershed innovation makes it convenient and affordable to deploy network devices such as Internet Protocol (IP) phones, wireless access points, and a growing host of other devices by eliminating the need for separate electrical power lines on each IP device. The Ethernet line does it all. Plug it in, and a device is ready for use.

In this way, PoE takes network convergence another step: the converged media network that carries data, voice and video together in a unified IP infrastructure can incorporate the power network too. Such integration brings with it intrinsic benefits like those of other types of network integration: simplified management, easier deployment, and less complexity. PoE saves time and money while making the network more flexible and cost-effectively adaptable to operational requirements.

Having clearly demonstrated its usefulness with IP phones and wireless access points, PoE is now inspiring the development of many other LAN devices, including video cameras, retail kiosks, point-of-sale devices, card scanners, industrial automation tools, and remote monitoring devices. There's even an Ethernet-powered electric guitar.

PoE is a young technology still in its first iteration. The rudimentary capabilities of the original standard were all that networkers needed to get started using PoE, and given its auspicious start, PoE has a highly promising future. But as with most standards, PoE will thrive only if it can evolve and build upon its basic functions.

In 2003 the Institute of Electrical and Electronics Engineers (IEEE) ratified the PoE standard, known as 802.3af. The 802.3af PoE standard works by injecting direct current (DC) power over Ethernet cable wires typically through LAN switches. Under the current standard it can deliver three levels of power: 4, 7 or 15.4 watts (the default if no request is made)

Now that so many devices—and people—rely on PoE, the standard can do better. The current standard leaves money on the table. While it allows delivery of three different wattages, often third party devices are being allocated more power than they need. A wireless access point, for example, might only need 7 watts, instead of the default 15.4 watts determined by the PoE standard. That extra power that can be used to power another access point or device is now unusable. While still being within the boundaries of the standard, that's over seven watts or 100% of potentially wasted power.

A watt here or a watt may not seem like much, but such waste multiplies rapidly with the spread of IP telephony and wireless communications deployments. And as the types of devices using PoE expand, the problems from poor power allocation will only mushroom. And the extra heat generated by the power raises other concerns, particularly more cooling requirements, adding up to extra costs for air conditioning, fans, or other environmental controls.

To address this concern, Cisco Systems has pioneered a more sophisticated control of PoE with its Intelligent Power Management technology. Intelligent Power Management allows users to better control power reservation, including setting predefined, per-port power allocation; identifying ports where power is not being used; reallocating power; and providing power prioritization. It also restricts high-powered devices from being plugged into ports designated as low-powered ports in the event that a switch runs out of available power. The basic benefit is that switches manage only the power necessary for running networked devices – no more, no less.

On the powered device end, Cisco also pioneered the use of intelligent devices. These devices through Cisco Discovery Protocol (CDP) have the ability to request the exact amount of power they require, beyond the simple three tier classification. All this without user or administrator intervention. So power allocation becomes even more precise allowing for even more environmentally friendly hardware and more cost-effective deployments.

Better power management can also be of great assistance in emergency situations. When electrical lines are knocked out by a storm a building or business switches to its emergency batteries or generators to keep their network running. Intelligent power management makes it possible to switch off power to selected devices, helping conserving energy for the most crucial devices. A company, for example, could shut off power to all IP phones except for one in each work area.

PoE can also regulate power in other ways, such as delivering less power to idle devices and boosting it when they are turned on. The current PoE standard delivers a constant rate of power.

While Cisco's advanced power management capability affects only its own LAN switches, widespread industry adoption will only further the value of PoE technology and the inherent benefits of convergence.

For instance, even with Intelligent Power Management, PoE cannot address the power needs of all networked devices. Under the 802.3af standard, PoE can only deliver a maximum of 15.4 watts. While enough for a wide-array of small devices, most laptops, personal computers and other commonly networked devices require more power. Cisco and other vendors now offer Power over Gigabit Ethernet. This continuing trend in innovation and implementation will enable a new breed of both high-speed and powered devices, ensuring the proliferation and continued evolution of PoE.

All networked devices need power, and the more the communications and power infrastructures can be integrated, the easier it will be to take advantage of these promising products. As with the converged network, the more intelligent PoE becomes, the more benefits it can provide. Even with current limitations, PoE –especially with advanced power management capabilities—holds more potential for improving the usefulness of the network. We are just starting to enjoy the benefits of PoE. Future innovations can make it possible for PoE to deliver much more power and support a host of new devices that we can only begin to imagine.

This article originally appeared on

Sam Bottros is a senior network engineer (CCIE #6978), LAN Switching Product and Technology Marketing, at Cisco Systems.

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