You Have the Power! (over Ethernet)

By James Donovan, Director of Global Solutions Management, SYSTIMAX Solutions -- Consulting-Specifying Engineer, 4/1/2005

Power over Ethernet continues to grow more popular, and many companies have already implemented PoE solutions. So what exactly should consultants know about this new technology?

PoE allows the transmission of electrical power over the same Ethernet infrastructure used for data transmission. It extends the capability of the Ethernet infrastructure and delivers power over high-quality category 5e/6 data cables, thereby eliminating the need for extraneous power adaptors, power cords and AC outlets.

The PoE standard, formally known as IEEE 802.3af, was ratified in June 2003. Prior to the adoption of this global standard, most PoE solutions were mutually incompatible proprietary standards. With the new standard in place, a wide array of PoE devices could be developed with some assurance of interoperability.

A variety of interoperable devices have already been introduced. These include Voice over IP (VoIP) phones, wireless local area network (WLAN) access points and security network cameras. The IEEE 802.3af project was driven by the proliferation of low-power devices that need to be connected to local area networks (LANs). Providing power to these network endpoint devices, in addition to the network connection, results in a cost-effective network infrastructure deployment.

The PoE architecture consists of two elements: the powered device (PD) and power-sourcing equipment (PSE). Two approaches have been adopted to supply power to a link via a PSE. One approach, which supplies power over the signal pairs (end-span), is intended for use by network equipment vendors. Another option is mid-span power insertion over the spare pairs (10BASE-T and 100BASE-TX networks) designed to support the installed base. Initially, the mid-span approach is a lower-cost solution for legacy networks since it will not require the replacement of the network equipment.

From a financial perspective, PoE holds the allure of cost savings by eliminating the need for installation of electrical outlets by certified electricians. PoE also provides IT managers with the flexibility to deploy networked devices in optimal locations. WLAN access points can be placed behind ceiling tiles, and security cameras can be placed to provide greater coverage without concern for the AC outlet tether. In addition, network management enables IT managers to monitor and manage powered devices remotely.

Providers of PoE also argue that they offer a more reliable power supply to networked devices, with PDs that are less susceptible to power surges, theft, interruption and disconnection.

And as a standards-based solution, PoE offers vendor-independent interoperability as well as backward compatibility with legacy Ethernet infrastructure. An added benefit of the international standard is that devices do not need separate cords and adapters for different countries.

Though PoE-enabled ports today probably make up only a small fraction of the installed port base for Ethernet LAN switches, in the near term, the use of PoE-powered devices will experience rapid growth as IT managers look to add PoE capabilities to their networks.