Wireless Parameters
4-8 Configuring the RoamAbout Access Point
RTS Threshold
RTS Threshold, also known as medium reservation, specifies the packet size, where
messages larger than the spec ifi ed si ze mu st us e t he RTS/ CTS ( Requ es t t o Sen d/Cl ea r
to Send) protocol. The default value, 2347, effectively turns off the RTS Threshold.
In a wireless network, only one wireless device transmits at a time. Each device can
sense transmissions from other devices in its network that use the same frequen cy. This
behavior is referred to as the Carrier Sense Multiple Access/Collis ion Avoidance
protocol (CSMA/CA).
The RTS Threshold is useful when collisions frequently occur at the AP. This can be
caused when the AP and another device transmit data to each ot her simulta neously. By
lowering the RTS Threshold on the AP:
•When a message is shorter than the RTS Threshol d, the AP t ransm it s data when it
senses that the medium is free. The RTS/CTS protocol is not used.
•When the message exceeds the thr eshold, the AP sends an RTS to the clien t (or
AP in a LAN-to-LAN configuration). The AP waits until the device responds wit h
a CTS message.
Lowering the RTS Threshold imposes additional network overhead that could
negatively affect the throughput performance. Therefore, you should only lower the
RTS Threshold when the wireless network experiences frame collisions and lost
messages.
Medium Reservation on the client is useful for resolving a hidden station problem,
where two or more clients cannot sense each other’s transmissions, causing frame
collisions and lost messages. This problem can occur with clients located at opposite
ends of the AP coverage area. If you have a hidden station problem, move the clients
or AP so that the devices can sense each other’s transmissions, if possi ble. Otherwise,
set Medium Reservation on the RoamAbout c lient to the Hidden Stations setting. For
a hidden station problem, change Medium Reservation on the client, not the AP.