Published In May 2001
Last month, we discussed the centralized fiber optic architecture and how it affected network design. This month, we’ll continue the discussion, looking at how this can affect the design and/or need for a telecommunications closet (TC). Within building cabling systems, the center of activity for the contractor is the TC. Here is where the cables from the desktop (horizontal cabling) mate with the backbone cables to the computer room or main telecommunications crossconnect. From the beginning, the telecommunications closet has been the location of interconnects for the telephones and with the advent of LANs, the home of hubs to connect PCs to the network. The TC is also the center of the design of an EIA/TIA 568 standard structured cabling architecture. Based on the design limits of unshielded twisted pair (UTP) cables, the TC provides a convenient location for the hubs. The 90-meter limitation of UTP cabling dictates that TCs be near clusters of PCs on the desktop. A typical TC is a busy place. Hundreds of cables enter it from all directions. Racks of patch panels interconnect horizontal cables to patchcords going to hubs. Hubs are awash in patchcords to the PCs and a few backbone cables, usually fiber optic, to the main computer room or TC. Usually one wall is devoted to telephone crossconnects, usually done with 66 punchdown blocks. Equal numbers of horizontal cables come in from the desktops and connect to multipair telephone company cables in the backbone. Besides all the communications cabling, the TC also includes power for all the equipment, a dedicated data ground and air conditioning to remove all the heat generated by the electronic equipment. The janitor’s mop bucket and stacks of empty boxes are not part of the original design! Ideally, the contractor is working on a new closet. Clean floors and walls are ready for installation of the mounting plywood and assembly of racks. The ceiling has space for ladder racks or cable trays. The architects have already marked locations for coring for the backbone cabling. Drawings are prepared showing where every cable goes and what its identification will be. The real world, of course, is quite different. Most projects entail working on an upgrade or moves, adds and changes (MACs). That means crawling over all the cables already there, tracing unidentified cables to make sure you move, add, or remove cables correctly. Cable trays are probably overloaded or cables are laid in helter-skelter fashion. Several new technologies may affect the nature of the TC. High-speed networking at Gigabit speeds or above are becoming commonplace in the backbone and beginning to appear on the desktop. Today, the preferred Gigabit Ethernet (GbE) cabling is multimode optical fiber. With the high-performance fibers now available, GbE can run hundreds of meters further on fiber than on Category 5e or even the pre-standard implementations of Category 6. The longer-distance capability of fiber optics means that many networks can operate directly from the desktop to the computer room. This centralized fiber optic architecture makes the TC unnecessary. Even at lower network speeds, new low-cost fiber optic interface electronics make centralized fiber optic architectures cost effective. By locating all the hubs in the main TC or computer room and cabling with fiber direct to the desktop, networks become much easier to manage. At most, the TC is used for passive connections from backbone cables to desktop runs, although this can be done in a simple wall box or ceiling fixture. Centralized fiber optic networks require power only at each end, which makes it unnecessary to provide power, grounds, and air conditioning (AC) in the TC. This greatly reduces the cost by perhaps as much as $10,000 to $20,000 per closet, plus operating costs for the AC. In fact, if the closet serves only as a passive interconnect, you may not need it at all, thus saving further costs. Voice over IP (VoIP) technology is being developed that allows your telephone to work over your Ethernet network. This capability alleviates the final need for the wall of 66 blocks for telephone cable interconnections, which is the TC. Your desktop only needs the Ethernet network connection, and if it’s over fiber optics in a centralized fiber architecture, the TC is totally unnecessary. “Early adopters,” those who are the first to try new technology, are already building networks like this and are finding them to indeed be more cost effective. Others continue doing it just like it was done in the last century! HAYES is founder of Fotec in Medford, Mass. He has written widely on fiber optics, including The Fiber Optics Technician’s Manual. He can be reached at Jh@jimhayes.com.