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Operational and Organizational Security: Incident Response • Chapter 11 627

Placing servers up too high also has its disadvantages if it is an insecure loca-
tion. Servers can be knocked off tables that are too narrow, rickety racks of routers
can be tipped over, and equipment can fall from precarious shelves. Before placing
equipment in a particular location, ensure that the location is safe from accident.

Shielding

As mentioned earlier, shielding can be used to prevent data signals from escaping
outside of an office. Not only can communications signals leak out of a prescribed
area, but unwanted signals can also leak in and interfere with communications.
Thus, shielding is also necessary to prevent data from being damaged in transmis-
sion from radio frequency interference (RFI) and electromagnetic interference
(EMI). RFI is caused by radio frequencies emanating from microwaves, furnaces,
appliances, radio transmissions, and radio frequency-operated touch lamps and dim-
mers. Network cabling can pick up these frequencies much as an antenna would,
corrupting data traveling along the cabling. EMI is cause by electromagnetism gen-
erated by heavy machinery such as elevators, industrial equipment, and lights.The
signals from these sources can overlap those traveling along network cabling, cor-
rupting the data signals so that they need to be retransmitted by servers and other
network devices.When EMI and RFI cause interference it is called “noise.”
To prevent data corruption from EMI and RFI, computers and other equip-
ment should be kept away from electrical equipment, magnets, and other sources.
This will minimize the effects of EMI and RFI, because the interference will dissi-
pate as it travels over distance.
When cabling travels past sources of EMI and RFI, a higher grade of cabling
should be used, which have better shielding and can protect the wiring inside from
interference. Shielded twisted-pair (STP) is a type of cabling that uses a series of
individually wrapped copper wires encased in a plastic sheath.Twisted-pair can be
unshielded or shielded.When the cabling is STP, the wires are protected with foil
wrap for extra shielding.

NOTE

For more information on cabling, please refer to Chapter 6,
“Infrastructure Security: Devices and Media.”

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