the range of 40 to 120 microns (a micron is one millionth of a meter, or about
0.00004 inch).
As the light pulse transverses the cable it loses power. This loss, called atten-
uation, is measured in decibels. The attenuation of fiber optic cables is depen-
dent on the wavelength. Multimode fiber optic cables operating at low
wavelengths may have attenuation less than 3.5 decibels per kilometer and less
than 1.5 decibels per kilometer at higher wavelengths.
Single-mode fiber optic cables have superior performance with maximum
attenuation of 0.5 to 1 decibel per kilometer and can be used anywhere in a
network but are generally used for longer distances. Multimode fiber optic
cables are utilized for shorter distances (less than a mile) and are found gener-
ally within buildings. Beyond the high bandwidth capacity of fiber optic cables
major benefits include immunity from electromechanical interference, immu-
nity from radio frequency interference, and use over longer distances.
Coaxial Cable
For many years coaxial cable was the cable of choice with extensive use in
video distribution systems, early Ethernet network installations, and connec-
tivity to many large mainframe computer systems. Coaxial cable is essentially
a wave guide transmitting radio and television frequencies down the cable and
is immune to electromechanical interference. It continues to be used for some
video transmission. However, with technical advances in IP video and the use
of “baluns” (which allow video signals to be transmitted over unshielded
twisted-pair cable) the use of coaxial cable is decreasing. Its use in a smart
building is generally minimal.
Wireless
Wireless connectivity is just a substitute for cabled connectivity. Wireless does
not and technically cannot provide the theoretical bandwidth of a physical
cable connection. However, wireless can provide mobility and is an excellent
option for connectivity in older buildings where pathways for cable may not
be available. The wireless technologies probably most useful for smart buildings
technology systems include Wi-Fi and an emerging technology, Zigbee.
Wi-Fi
Wireless Fidelity (Wi-Fi) systems basically replace cabled Ethernet connec-
tions with a wireless device. Current Wi-Fi systems operate in two unlicensed
16 Smart Building Systems for Architects, Owners, and Builders