H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 370)

354
Item Description
RTS (CTS)
There are two data collision avoidance mechanisms, RTS/CTS and CTS-to-self.
• RTS/CTS—In this mode, an AP sends an RTS packet before sending data to
a client. After receiving the RTS packet, all the devices within the coverage
of the AP will not send data within the specified time. Upon receiving the
RTS packet, the client sends a CTS packet, ensuring that all the devices
within the coverage of the client will not send data within the specified time.
The RTS/CTS mechanism requires two frames to implement data collision
avoidance, and thus has a higher cost.
• CTS-to-Self—In this mode, an AP uses its IP address to send a CTS packet
before sending data to a client, ensuring that all the devices within the
coverage of the AP will not send data within the specified time. The
CTS-to-Self mechanism uses only one frame to avoid data collision.
However, if another device is in the coverage of the client, but not in the
coverage of the AP, data collision still may occur.
Compared with RTS/CTS, CTS-to-Self reduces the number of control frames.
However, data collisions still occur when some clients are hidden and thus
cannot receive the CTS frames sent by the AP. Therefore, the RTS/CTS
mechanism can solve the data collision problem in a larger coverage than
RTS/CTS.
RTS (CTS) Threshold
If a frame is larger than the RTS (CTS) threshold, the data collision avoidance
mechanism is used.
A smaller RTS/CTS threshold causes RTS/CTS packets to be sent more often,
thus consuming more bandwidth. However, the more often RTS/CTS packets
are sent, the quicker the system can recover from collisions.
In a high-density WLAN, you can decrease the RTS threshold to reduce
collisions in the network.
IMPORTANT:
The data collision avoidance mechanism occupies bandwidth. Therefore, this
mechanism applies only to data frames larger than the RTS/CTS threshold.
DTIM Period
Number of beacon intervals between delivery traffic indication message
(DTIM) transmissions. The AP sends buffered broadcast/multicast frames when
the DTIM counter reaches 0.
Long Retry Threshold
Number of retransmission attempts for unicast frames larger than the RTS/CTS
threshold.
Short Retry Threshold
Number of retransmission attempts for unicast frames smaller than the
RTS/CTS threshold if no acknowledgment is received for it.
Max Receive Duration Interval for which a frame received by an AP can stay in the buffer memory.
Enabling a radio
1. Select Radio > Radio from the navigation tree to enter the radio setup page.