ZyAIR G-220 User’s Guide
Wireless Station Mode Configuration 2-5
A large Fragmentation Threshold is recommended for networks not prone to interference while you
should set a smaller threshold for busy networks or networks that are prone to interference.
If the Fragmentation Threshold value is smaller than the RTS/CTS Threshold value (see previously)
you set then the RTS (Request To Send)/CTS (Clear to Send) handshake will never occur as data frames
will be fragmented before they reach RTS/CTS Threshold size.
2.4 RTS/CTS Threshold
A hidden node occurs when two stations are within range of the same access point, but are not within range
of each other. The following figure illustrates a hidden node. Both stations are within range of the access
point (AP) or wireless gateway, but out-of-range of each other, so they cannot “hear” each other, that is
they do not know if the channel is currently being used. Therefore, they are considered hidden from each
other.
Figure 2-6 RTS Threshold
When station A sends data to the AP, it might not know that the station B is already using the channel. If
these two stations send data at the same time, collisions may occur when both sets of data arrive at the AP
at the same time, resulting in a loss of messages for both stations.
RTS/CTS Threshold is designed to prevent collisions due to hidden nodes. An RTS/CTS Threshold
defines the biggest size data frame you can send before an RTS (Request To Send)/CTS (Clear to Send)
handshake is invoked.
When a data frame exceeds the RTS/CTS Threshold value you set (between 0 to 2432 bytes), the station
that wants to transmit this frame must first send an RTS (Request To Send) message to the AP for
permission to send it. The AP then responds with a CTS (Clear to Send) message to all other stations within
its range to notify them to defer their transmission. It also reserves and confirms with the requesting station
the time frame for the requested transmission.
Stations can send frames smaller than the specified RTS/CTS Threshold directly to the AP without the
RTS (Request To Send)/CTS (Clear to Send) handshake.
