Payoff for Power Over Ethernet

Lower costs, greater flexibility for deploying wireless access may outweigh UPS concerns.

The IEEE 802.3AF Power-over-Ethernet task force, which met last month at Cisco Systems Inc.s headquarters in San Jose, Calif., is slated to finish its work in June, but vendors are preparing to release products based on the specification now.

Based on eWEEK Labs work with wireless access points and VOIP (voice-over-IP) telephone handsets, we think the 802.3af-compliant products coming onto the market will be a big boon for IT managers.

Many of the benefits and drawbacks of power over Ethernet that weve discussed in the past remain the same, however. The major effort of preparing for these new devices has to do with allotting wiring closet real estate and doing network remediation.

The payoff should be significantly reduced costs and far greater flexibility for deploying wireless access and remote cameras, among a wide array of new data devices that will likely hit the market in the months to come.

Get ready for a new class of network remediation chassis to be added to the rack. Power over Ethernet requires that low-voltage DC current be added to the two wire pairs in Category 3 or 5 cabling, so new devices, called midspan PSE (Power Sourcing Equipment), are needed. PSE devices sit next to Ethernet switches and look a lot like switches.

Midspan PSEs are available from PowerDsine Ltd., a company that has had employees involved in the formation of the 802.3af specification since the beginning of the working group, in 1999.

These midspan devices will require precious rack space and an AC outlet. In addition, these devices will need a UPS (uninterruptible power supply) to work during power outages.

When we were frequently reviewing UPS systems in the mid-90s, one thing became apparent that should still be foremost in the minds of IT managers: A significant number of UPS systems dont work when the power goes down.

The ramifications for network remediation become clear when you consider that a UPS—whether its a central building generator connected to an AC circuit or individual UPSes in wiring closets—will be necessary to provide the juice for the power-over-Ethernet devices.

In addition, the effect of bundled power-over-Ethernet cables is untested, as far as we know. In most of the cable runs in the San Francisco offices of Ziff Davis Media Inc. (publisher of eWEEK), for example, it is common to see bundles of 10 to 50 network cables running from the server room to various parts of the building. As power over Ethernet makes its way into production, the effects of heat and electromagnetic interference are definitely worth watching—although this might be of only moderate concern because the specification currently calls for low voltage (less than 13 watts).

Equipment makers will likely bring out all sorts of PSEs after the 802.3af specification is ratified. The guidelines hammered out in San Jose call for extensive checking to ensure that devices connected to a PSE or other power-over-Ethernet device can, in fact, accept power. The safeguards, which depend on a device recognizing a signal and returning a confirming signal, should be enough to make sure no equipment is damaged by inadvertently sending current down the line.

The specification also calls for power ports to cut off current within a fraction of a second if a device at the end of the socket is no longer operating. Thus, devices might be controlled remotely via their power supply.

Underpowered power-over-Ethernet products could appear on the market; we believe low-cost power-over-Ethernet switches are the most likely suspects. In such a case, although all the switch ports would be capable of providing power, they couldnt all be turned on at the same time.

This isnt necessarily a bad thing, of course. Except for VOIP implementations, it isnt likely that every device on a particular switch will need power. However, its important to be aware of this possible shortcoming.

Senior Analyst Cameron Sturdevant can be contacted at cameron_sturdevant@