Cabling Your Office for the Future

by Brian McConnell

If you are thinking about buying a new phone system or upgrading your Local Area Network (LAN), now is a good time to think about having your office rewired to support today's and tomorrow's voice and data communications services.

Rewiring your office does not need to be an ordeal, nor does it need to require a major capital investment since, in most cases, you can use ordinary copper wiring throughout most of your office.

This article is intended as a tutorial for small and mid-sized offices which are facing these issues. This is not intended to cover the entire range of network cabling issues, in particular for large offices with long cable runs or remote locations.

Multimedia cabling - an introduction
While there has been a lot of talk about combining voice, data, and video traffic over a single multimedia network, the most likely outcome, for the next few years anyway, is that separate wiring will still be required for voice and LAN traffic. Fortunately, with the emergence of 100BaseT Ethernet, in most cases, you should be able to use twisted-pair wiring now, and in the future, to deliver a broad range of data and voice services to your desktops. Read "Premises Cabling"

Each desktop in your office should be served with a multi-purpose jack which includes several types of wiring interfaces: 6-wire RJ-14 for telephone service, RJ-45 for 10BaseT and 100BaseT service, and a spare UTP (unshielded twisted pair) cable which hangs loose behind the modular jack panel for future use.

Wiring can be brought to the jack in 1 of 2 ways: either via in-wall wiring, or via floor wiring concealed by plastic wiring covers. If you can easily get behind your walls to run cable, this will produce neater results. If you are in an older building or use modular office furniture, you should be able to run cabling over your drop ceilings, and then use modular wiring covers to protect cable runs through large work areas.

Network/LAN wiring
Use Category 5 UTP cabling to link LAN workstations to a centrally located 10BaseT or 100BaseT Ethernet hub. For small networks, unmanaged hubs, such as those made by Allied Telesis, are sufficient for lightly utilized LANs. A hub functions in much the same way as an intercom or PBX system, except it manages the routing of traffic through your LAN. With a hub, you can connect and disconnect stations from the LAN without disrupting other users. Read "LAN Wiring"

Generally speaking, copper wiring is fine for most smaller LANs. Contrary to popular myth, fiber-optic cabling does not automatically mean more bandwidth. Copper is capable of delivering high data rates (i.e., 100 Mbps Ethernet), but is sensitive to the distance of the cable run. Fiber's strength is in delivering high data rates over long distances (i.e., between buildings, in place of long cable runs, etc.). However, it is generally not cost effective to connect workstations directly to a fiber cable run. The best place to use fiber is in your backbone, and then only if you need to be able to deliver high data rates over long distances.

Internet connectivity
Seamless connectivity to the internet is accomplished using a device called a router. A router does what its name implies, routes packets broadcast over your LAN to remote destinations outside your LAN. Routers come in many different configurations. The most important feature in choosing a router is the type of external connection it supports. For small offices which do not need 24-hour connectivity to the internet, ISDN routers provide up to 128 Kbps throughput to an internet service provider. For offices which need 24-hour connectivity (i.e., for a locally hosted web site, mail server, etc.), Frame Relay is a better option than ISDN as it can provide data rates from 64 Kbps to 1.5 Mbps and is generally offered on a flat-rate basis instead of a per-minute basis (as is the case with ISDN). If higher speed connectivity is required, you should look into SMDS, Cable, or DSL service (which can range from 1.5 Mbps to 52 Mbps).

Voice wiring
Generally speaking, you want to provide 6-wire cable to every location where you may wish to place a telephone station. Although many phone systems require only 2 wires per station, others use the remaining 4 wires for signaling and remote power. Better to over build your wiring than to have to go back and rewire your office 2 years from now.

Voice circuits are much less demanding in terms of the wiring required for them. You do not need Category 5 cable for ordinary voice circuits because high-frequency signals are never transmitted over ordinary voice circuits. If you can afford it, it won't hurt anything to use Category 5 UTP wiring for voice lines, and this may not be a bad idea since there is talk of integrating voice into a new standard called isosynchronous Ethernet or isoE as it's being called in the industry. isoE bundles 96 voice circuits into a 10 Mbps Ethernet for simultaneous voice/LAN service on a single cable.

isoE probably is the trend of the future, but for now there is very little equipment for this standard, and the per-seat cost of equipping workstations with isosynchronous adapters is currently quite high compared to data-only Ethernet adapters. The migration to isoE is, therefore, some years in the future. Worth preparing for? If you want to leave this option open for the future, use Cat5 UTP wiring for your telephone wiring, too. It's overkill, but it might come in handy in a few year's time.

The wiring closet
Your wiring should be terminated by a centrally located patch bay with modular jacks. The LAN wiring should be terminated by RJ-45 (8-wire) modular jacks. The voice wiring should be terminated by RJ-14 (4 or 6-wire) modular jacks. Patch cords are then used to connect the LAN jacks to a hub and/or router, and to connect voice jacks to a PBX or intercom system. By using modular connectors, you make it much easier to keep your wiring nice and neat.