Westermo RM-80 - Manual (Page 50)

50 6193-4201
Appendix B GLOSSARY
ACK Acknowledgment.
Access point An access point is the connection that ties wireless communication
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.
Bridge
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 connecting 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 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 method rather
than collision detection must be used, because the standard employs
half duplex radios—radios capable of transmission or reception—
but not both simultaneously. Unlike conventional wired Ethernet
nodes, a WLAN station cannot detect a collision while transmitting.
If a collision occurs, the transmitting 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 transmission of the ACK packet before any other node can
begin transmitting 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.