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
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.
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.
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).
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.