There are multiple levels of redundancy that are important when deploying a Power over Ethernet (PoE) solution for IP telephony. One of the things that people have gotten used to is that when the power fails, the phone system should continue to operate. If power for the IP phones is provided by PoE switches, it is necessary to have a battery backup or redundant source of power for when there is a power failure.
In addition to this, there needs to be standard path redundancy for the PoE switches. This can be easily provided if the PoE switches support the Spanning Tree Protocol (STP). This allows for purposeful redundant paths to be set up in the network that can become active automatically when the primary path fails.
This was first published in August 2005