Infrastructure Awareness
LAN media

Examine the media types that make up the network. For most connections the customer will most likely use some type of copper UTP cabling. Category 5 copper media can be run to a maximum distance of 100 m (328 ft) without a repeater or hub. Optical fiber can be run for miles if necessary.

While some facilities LAN media is fiber optics, most company networks use a combination of fiber and copper. The fiber acts as the main backbone of the network and the copper runs to the desktop. If the facility uses fiber cabling throughout, be sure to advise the customer that the APs only provide RJ-45 connections and that a media transceiver will be needed for each of the APs. The required media transceivers can be a significant cost.

The most frequently used cable for modern networks is Category 5 (Cat 5), unshielded twisted pair (UTP), shown in Figure . Category 5 cable consists of eight strands of copper, grouped in pairs. Category 5 UTP cable can be run a maximum distance of 100 m (328 ft). Category 5 cable is available in plenum and nonplenum. Building construction, as well as local and state building codes, will determine which type of cabling must be used. The plenum is the space between the drop tile ceiling and the true ceiling. In a plenum environment, this space is used for air return. In the event of a fire, the nonplenum PVC sheath, or outer jacket, can melt and produce toxic fumes.

Since network cables are traditionally run in the plenum, toxic fumes will then be circulated throughout the building. Therefore, plenum cable must be used in these facilities. All other equipment installed, including APs, must also be plenum rated. Plenum cables have a different sheath that will not melt as easily and will not give off toxic fumes. Plenum cable is easily identified. The sheath of plenum cable is much stiffer and harder to work with than standard Category 5 cable. The cable will also be marked with a code. CMP, for example, indicates a plenum rated, unshielded cable.

Some easy ways to identify a plenum environment are suspended ceiling tiles, a lack of insulation above the ceiling tiles, and firewalls. Some local and state building codes require plenum cable regardless of the environment. A nonplenum environment is one where the air return is ducted. When the air return is ducted there is very little chance that the toxic fumes could spread in the event of a fire.

In this type of environment it may be suitable to use a general purpose, PVC type cabling. Some indications of a nonplenum environment are an abundance of duct work above the ceiling tiles, a lack of firewalls, and insulation above the ceiling tiles. These cables will also have identifying codes. CM, for example, indicates a nonplenum unshielded cable.