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It's time to run power over Ethernet

David Berlind ZDNet US

Published: 11 Mar 2003 16:10 GMT

If you haven't done so already, perhaps now is a good time to start looking into migrating your existing network infrastructure to one that supports the IEEE 802.3af draft standard, which makes possible the distribution of power over Ethernet cabling (PoE). If you're at a green field where a new network is going in -- especially a wireless one -- then you should be looking at making PoE an integral part of your design.

The chief benefit is rather obvious. With PoE, a single wire delivers both communications and power, so you don't need an electrical outlet near the device at the end of an Ethernet run (referred to by the draft standard as the Data Terminal Equipment or DTE). This can be particularly handy for devices that need to be located where a power source isn't convenient: wireless access points (for WLANs), net-enabled security cameras, and Voice over IP-based telephones are good examples. Of course, you'll need devices at both ends of the wire that support 802.3af. Most new and legacy equipment does not support PoE. In fact, manufacturers are just getting around to doing interoperability testing of PoE equipment at the University of New Hampshire.

You should know some other things about the conveniences of running PoE. One of them has to do with servicing the DTE. In the two years I've been operating my two-access point WLAN, I've only had to perform a hard reboot a few times. However, in a corporate scenario with hundreds or thousands of access points, power cycling could become a daily activity. Depending on how your technicians bill for time, getting to and from the access point could become expensive. Imagine all that wasted time just to get to the equipment, pull the plug out and put it back in.

Now imagine that you're sitting at an Simple Network Management Protocol (SNMP) management console like HP OpenView and, instead of sending a technician out to the misbehaving access points, you use a few mouse clicks to turn off the port on an 802.3af-compliant Ethernet switch that corresponds to the access point and then, with another mouse click, you turn it back on.

It gets better. How many times has your power gone out but the phones kept working? It's a lot easier to keep your WLAN (and your VoIP telephones, Net cams, and other DTE) running during a power outage when you deliver the power to them over Ethernet. For example, if you want to keep a non-PoE access point running during an outage, it would need a separate uninterruptible power supply (UPS). With PoE, you only need to back up the switch in your wiring closet with a UPS. Granted, the UPS might have to be a big honkin' UPS (depending on how many devices are connected to the switch), but centralising UPS activity in situations where the DTE can't go could yield dramatic cost savings. One of the big reasons that companies have shied away from VoIP-based telephony is because they are so accustomed to not losing their phone service -- even during a power outage.