160
Networking Fundamentals
Wireless Access
Point (WAP)
a wireless network
device that provides
a connection
between a wireless
network and a cable-
based network and
controls the fl ow of
all packets on the
wireless network.
Distances vary by manufacturer and by location conditions such as
placement of metal cabinets and building materials. The maximum power output
of the device has a direct relationship to data throughput. Packet loss is generally
caused by radio interference or excessive distance between two devices. When
packet loss increases, the data rate decreases. The data rate is automatically
adjusted to a lower rate when an excessive number of packets are lost. The data
rate continues to be lowered until an acceptable packet loss is reached. The more
powerful the signal, the less interference can disrupt the signal. This means that
there will be fewer packets lost. Consequently, data rate is better when the signal
is more powerful. The maximum transmission power rating for a wireless device
is set by the FCC. Do not attempt to memorize distances because they are not
standard.
Radio Wave-Based Networking
Radio wave-based networks are rapidly becoming the choice of many
networking systems because of the fast and easy installation and the convenience
of no wires. A simple wireless network, such as one designed for home or
business use, consists of two or more computers with wireless network adapters.
Figure 4-13 shows a USB wireless network adapter.
Wireless Access Points
While not required, most wireless networks contain a Wireless Access Point
(WAP) also referred to as an access point (AP). A Wireless Access Point (WAP)
provides a connection between a wireless network and a cable-based network.
Figure 4-11.
Orthogonal
frequency-division
multiplexing (OFDM)
is used in conjunction
with the U-NII
frequency ranges to
achieve a data rate as
high as 54 Mbps. Each
of the U-NII frequency
ranges is 100 MHz
wide. This bandwidth
is divided into three
20-MHz channels,
which are further
divided into fifty-two
300-kHz channels.
5-GHz
frequency
band
20 MHz
20 MHz
20 MHz
20 MHz
Orthogonal Frequency-Division Multiplexing (OFDM)
100-MHz
bandwidth
52 300-kHz
channels
Figure 4-12.
U-NII classifications
and their
characteristics.
U-NII 1 5.15 GHz–5.25 GHz 50 mW Indoors
U-NII 2 5.25 GHz–5.35 GHz 250 mW Indoors/outdoors
U-NII 3 5.725 GHz–5.825 GHz 1 W Outdoors
Classification Frequency Range Power Comment