Every commercial building—including retail stores, office buildings, gyms, dorms, and schools—has some form of network connectivity. These networks’ complexity varies from “all wireless” access to overhead Category 6A cabling with PoE support for telephone, security, fire detection, and other systems. Figure 11-1 illustrates the basic components of a building network.
Figure 11-1 Building a Local Area Network
Outside access to the Internet or a corporate network enters through the equipment room or building distribution frame (BDF).
The following sections describe items of interest in Figure 11-1.
Equipment Closet (Building Distribution Frame)
In physical relay (crossbar and Strowger), telephone networks, wires, and equipment were hung off or tied to large, complex metal frames. Every building had a building entry point (BEP), often a piece of plywood attached to a wall in an equipment room. A small BDF would be constructed in a basement or first-floor room in larger buildings that feed other buildings. Over time, the BEP became associated with the BDF, and many engineers use the two terms interchangeably.
In some networks, the main distribution frame (MDF) overlaps with the BDF. Sometimes, however, a network becomes large enough to have a separate facility used to connect all the buildings together. This facility is often called the MDF.
Wiring Closet (Intermediate Distribution Frame)
In physical relay (crossbar and Strowger) telephone networks, small frames containing primarily wiring were called intermediate distribution frames, or IDFs. These IDFs might be on each building floor or between the main switching frame (mainframe) and the BDFs. An IDF is often used for any “intermediate” wiring closet or structure.
Server Room
Most buildings, particularly offices not physically located on a corporate campus ( remote locations), have a few servers for handling local storage and computing requirements. A small office might need to support local voice service or building access control.
The room containing local servers is often called the server room.
Routers and servers are often—but not always—located in the same room as the BDF.
Riser
Risers are vertical conduits or spaces designed to hold cables running between floors. Most buildings have only one or two risers. Wiring on each floor runs from a wiring closet horizontally.
Wi-Fi Access Points
Commercial Wi-Fi access points often draw power off a switch in the wiring closet (IDF) through PoE. Large-scale Wi-Fi networks supporting large commercial buildings and campuses often require a site survey to uncover interference sources and signal-blocking structures. Engineers use information about the site to select the placement, which channels to use, and the transmission power of each access point.
Zoned Access
Larger buildings often use zoned access, shown in Figure 11-1 as Z1, Z2, Z3, and Z4. Rather than multiple cables from every desk—or other location with network equipment—directly to the wiring closet, a series of patch panels or switches is installed throughout the building. Zone access adds some complexity to the original design, but it also adds a lot of flexibility.