The proposed IEEE 802.3af standard for supplying power over Ethernet cabling will ease deployment of IP telephones and wireless access points, and reduce the cost of powering the devices. Currently in draft status, the standard is expected to be ratified by June.

Traditionally, IP phones have required two connections: one to the enterprise LAN and another to the electrical AC network. Other network devices, such as wireless LAN access points, laptop computers and Web cameras, also have required both types of connections. Given the increasing number of LAN devices in corporations, wiring AC connections for each of them is a costly task.

Network managers typically install an uninterruptible power supply (UPS) for each device, or create a separate back-up AC network, but both alternatives can be prohibitively expensive. Furthermore, many of these devices must be installed in unusual locations for optimal operation. To achieve effective radio coverage, wireless LAN access points are mounted above ceiling panels, where it is rare to find an AC outlet.

Commonly known as Power over Ethernet, the 802.3af specification eliminates the need for additional outlets and the labor cost incurred from contracting electricians to install them.

What's more, the technology supports a point-to-multipoint power distribution architecture, parallel to the data network. This lets managers use a single UPS at the network core to back up multiple scattered devices on the LAN. 802.3af also provides remote access and management via SNMP Web-based control.

802.3af defines a way to build Ethernet power-sourcing equipment and powered terminals. The specification involves delivering 48 volts of AC power over unshielded twisted-pair wiring. It works with existing cable plant, including Category 3, 5, 5e or 6; horizontal and patch cables; patch-panels; outlets; and connecting hardware, without requiring modification.

The current delivered to each node is limited to 350 milliamps. The total amount of continuous power that can be delivered to each node, taking into account some power loss over the cable run, is 12.95 watts. IP phones and wireless LAN access points typically consume 3.5 to 10 watts.

Power is carried on two wire pairs, to comply with safety standards and existing cable limitations. 802.3af power sourcing equipment contains a detection mechanism to prevent sending power to noncompliant devices. Only terminals that present an authenticated Power over Ethernet signature will receive power, preventing damage to other equipment.