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| 3.6 |  | Implementing Physical Layer Solutions |
| 3.6.5 |  | Redundancy |

When installing or maintaining a network it is important to have contingencies in place to counter physical layer problems. The presence of an Uninterruptible Power Supply (UPS), surge protectors, or line filters can protect a network from short term power interruptions, brownouts, and power spikes.

Core layer hardware should have replacement units on hand. It is a good idea to install modular hardware wherever possible. In that way the failure of a single module will not result in the entire device being taken off line. Having replacement modules in store is also cost effective. In the event of component failure, the modules can be interchangeably used in a variety of compliant chassis.

When changes are made to device or network configurations, back-up copies of the previous functional configurations should be on hand in the event of network failure resulting from these changes. In this way network failure duration can be minimized and troubleshooting can occur independent of the network.

Having additional cabling and testers on hand is also highly recommended. On network installation it is important to protect backbone cabling from damage by running it through wall, floor, or roof cavities. In the event of damage to patch cables or damage to backbone cabling it is essential that replacement cable be on hand to shorten outage duration.