ZyAIR Wireless LAN Utility
5-2
Advanced Configuration
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.
You should only configure
RTS/CTS Threshold
if the possibility of hidden nodes exists on your network
and the “cost” of resending large frames is more than the extra network overhead involved in the RTS
(Request To Send)/CTS (Clear to Send) handshake.
If the
RTS/CTS Threshold
value is greater than the
Fragmentation Threshold
value (see next), 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.
Enabling the RTS Threshold causes redundant network overhead that could
negatively affect the throughput performance instead of providing a remedy.
5.1.2 Authentication Mode
The IEEE 802.11b standard describes a simple authentication method between the wireless clients and AP.
Three authentication modes are defined: Auto, Open and Shared.
Open authentication mode is implemented for ease-of-use and when security is not an issue. The wireless
station and the AP do
not
share a secret key. Thus the wireless stations can associate with any AP and listen
to any data transmitted plaintext.
Shared authentication
mode involves a shared secret key to authenticate the wireless station to the AP. This
requires you to enable a security feature and specify a shared secret key (usually the WEP encryption and
WEP key) on both the wireless station and the AP.
Auto authentication mode allows the ZyAIR to switch between the open and shared key authentication
modes automatically. Use the auto mode if you do not know the authentication mode of the other wireless
clients.
5.1.3 Preamble Type
A preamble is a signal used to synchronize the transmission timing in your wireless network. There are two
preamble modes: Long and Short.
