Figure 4-5 Rts Threshold - ZyXEL Communications ZYAIR 200 User Manual

ZyAIR 200 Wireleass LAN USB Adapter
Short – The optional "Short preamble and header" is intended for applications where maximum throughput
is desired and interoperability with legacy and non-short preamble capable equipment is not a
consideration.
RTS Threshold
The RTS Threshold prevents the Hidden Node problem. Hidden Node is a situation in which two stations
are within range of the same Access Point, but are not within range of each other. The following figure
illustrates an example of the Hidden Node problem. Both stations (STA) are within range of the Access
Point, however, they cannot hear each other. Therefore, they are considered hidden nodes from each other.
When a station starts data transmission with the Access Point, it might not notice that the other station is
already using the wireless medium. When these two stations send data at the same time, they might collide
when arriving simultaneously at the Access Point. The collision will most certainly result in a loss of
messages for both stations.

Figure 4-5 RTS Threshold

Thus, the RTS Threshold mechanism provides a solution to prevent data collisions. When you enable RTS
Threshold on a possible hidden station, this station and its Access Point will use a Request to Send/Clear
to Send protocol (RTS/CTS). The station will send an RTS to the Access Point, informing that it is going to
transmit the data. Upon receipt, the Access Point will respond with a CTS message to all stations within its
range to notify all other stations to defer transmission. It will also confirm with the requesting station that
the Access Point has reserved it for the time frame of the requested transmission.
Normally, the Disable option (default) is selected when you are not concerned with the Hidden Node
problem. When the Hidden Node problem becomes an issue, please select Enable and specify the packet
size. The RTS function will be activated if the packet size exceeds the value you set. It is highly
recommended that you set the value ranging from 0 to 2432.
4-8 Utility Setup and Configuration