Is there any downside to PoE?

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Quite frankly, I love those little gadgets you can plug right into Ethernet, but there are some caveats. For one, a proliferation of Ethernet "micro-nodes" means more switch ports required and perhaps upgrades to support PoE. Historically, we've gone from shared cable (the original Ethernet), to hubs, to switches and hubs, to a switch port for every user. Now imagine a 10:1 ratio of switch ports-to-users in the not-so-distant future.

Computing the power and cooling requirements for our wiring closets and data centers will become even more critical as we expand into PoE. Even though PoE is low voltage and relatively low power, a large number of PoE ports requires careful consideration of the number of PoE devices drawing power, how much each device draws, and ultimately switch power budgets.

We will also need to manage a much larger number of IP addresses and devices. These micro-nodes are intelligent IP devices just like the big stuff. Soon, the combined number of access points, web/security cameras, loud speakers/PA systems, clocks, and other devices will eclipse the number of users. Do such nodes have their own VLAN? IP space? Who's responsible for security and hacking? Identifying rogue nodes? How do we identify problems at the PoE electrical layer? Overdrawn switches?

Finally, watch out if you are attempting to wire your own injector. Or perhaps a more likely scenario is inadvertently wiring a jack or patch cable wrong. There are several web sites out there with precautionary notes like "WARNING - doing this wrong could SERIOUSLY FRY your access point and may void your warranty - proceed with caution!"

This was first published in September 2004

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