Page 789 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

the ESSID in order to differentiate multiple base stations
supporting a single extended wireless network.

Wireless Channels

Within the assigned frequency of the wireless signal are
subdivisions of that frequency known as channels. Think of
channels as lanes on the same highway. In the United States there
are 11 channels, in Europe there are 13, and in Japan there are 14.
The differences stem from local laws regulating frequency
management (think international versions of the United States’

Federal Communications Commission).

Wireless communications take place between a client and access
point over a single channel. However, when two or more access
points are relatively close to each other physically, signals on one
channel can interfere with signals on another channel. One way to
avoid this is to set the channels of physically close access points as
differently as possible to minimize channel overlap interference.

For example, if a building has four access points arranged in a line
along the length of the building, the channel settings could be 1, 11,
1, and 11. However, if the building is square and an access point is
in each corner, the channel settings may need to be 1, 4, 8, and 11.

Think of the signal within a single channel as being like a wide-
load truck in a lane on the highway. The wide-load truck is using
part of each lane to either side of it, thus making passing the truck

in those lanes dangerous. Likewise, wireless signals in adjacent
channels will interfere with each other.

Securing the SSID

Wireless networks are assigned a service set identifier (SSID) (either
BSSID or ESSID) to differentiate one wireless network from another.