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Appendix B
GLOSSARY
ACK
Acknowledgment.
Access point
An access point is the connection that ties wireless communica-
tion devices into a network. Also known as a base station, the
access point is usually connected to a wired network.
Antenna Gain
Antennae don’t increase the transmission power, but focus the
signal more. So instead of transmitting in every direction
(including the sky and ground) antenna focus the signal usually
either more horizontally or in one particular direction.
This gain is measured in decibels
Bandwidth
The amount of ”transportation” space an Internet user has at
any given time.
Collision avoidance
A network node characteristic for proactively detecting that it
can transmit a signal without risking a collision.
Crossover cable
A special cable used for networking two computers without the
use of a hub. Crossover cables may also be required for con-
necting a cable or DSL modem to a wireless gateway or access
point. Instead of the signals transferring in parallel paths from
one set of plugs to another, the signals ”crossover.” If an eight-
wire cable was being used, for instance, the signal would start
on pin one at one end of the cable and end up on pin eight at
the other end. They ”cross-over” from one side to the other.
CSMA/CA
CSMA/CA is a ”listen before talk” method of minimizing (but
not eliminating) collisions caused by simultaneous transmission
by multiple radios. IEEE 802.11 states collision avoidance meth-
od rather than collision detection must be used, because the
standard employs half duplex radios (radios capable of transmis-
sion or reception) but not both simultaneously. Unlike conven-
tional wired Ethernet nodes, a WLAN station cannot detect a
collision while transmitting. If a collision occurs, the transmit-
ting station will not receive an ACKnowledge packet from the
intended receive station. For this reason, ACK packets have a
higher priority than all other network traffic. After completion
of a data transmission, the receive station will begin transmis-
sion of the ACK packet before any other node can begin trans-
mitting a new data packet. All other stations must wait a longer
pseudo randomized period of time before transmitting. If an
ACK packet is not received, the transmitting station will wait for
a subsequent opportunity to retry transmission.