Hardware Reference
In-Depth Information
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Wireless repeaters/range extenders
—A repeater can stretch the range of an existing
wireless network. Some can also serve as access points or wireless bridges.
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Specialized antennas
—The “rabbit ears” antennas used by most access points and
routers are adequate for short distances, but longer distances or problems with line-
of-sight reception can be solved by attaching high-gain replacements for the originals,
or by attaching more specialized directional antennas, possibly on extension cables to
mount them higher for greater range.
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Signal boosters
—In addition to or as an alternative to replacement antennas, some
vendorsalsosellsignalboostersthatpiggybackontoanexistingaccesspointorrouter.
Note that, in most cases, these signal boosters are vendor specific.
Wireless Network Logical Topologies
Wirelessnetworkshavedifferenttopologies,justaswirednetworksdo.However,wireless
networks use only two logical topologies:
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Star
—The star topology, used by Wi-Fi/IEEE 802.11-based products in the infra-
structuremode,resemblesthetopologyusedby10BASE-TandfasterversionsofEth-
ernet that use a switch (or hub). The access point takes the place of the switch because
stations connect via the access point, rather than directly with each other. This meth-
od is much more expensive per unit but permits performance in excess of 10BASE-T
Ethernet speeds and has the added bonus of being easier to manage.
•
Point-to-point
—Bluetooth products (as well as Wi-Fi products in the ad hoc mode)
use the point-to-point topology. These devices connect directly with each other and
require no access point or other hub-like device to communicate with each other, al-
though shared Internet access does require that all computers connect to a common
wireless gateway. The point-to-point topology is much less expensive per unit than a
startopology.Itis,however,bestsuitedfortemporarydatasharingwithanotherdevice
(Bluetooth) and is currently much slower than 100BASE-TX networks.
Figure 17.19
shows a comparison of wireless networks using these two topologies.
Figure 17.19
A logical star topology (left) as used by IEEE 802.11-based wireless Ethernet in infrastruc-
ture mode compared to a point-to-point topology as used by Bluetooth and 802.11 in ad hoc mode (right).