H3C WA2612-AGN Web-Based Configuration Manual page 191

Item
Fragment Threshold
Beacon Interval
RTS (CTS)
RTS (CTS) Threshold
DTIM Period
Long Retry Threshold
Description
Specify the maximum length of frames that can be transmitted without
fragmentation. When the length of a frame exceeds the specified fragment
threshold value, it is fragmented.
•
In a wireless network where error rate is high, you can decrease the
fragment threshold by a rational value. In this way, when a fragment of a
frame is not received, only this fragment rather than the whole frame needs
to be retransmitted, and thus the throughput of the wireless network is
improved.
•
In a wireless network where no collision occurs, you can increase the
fragment threshold by a rational value to decrease acknowledgement
packets and thus increase network throughput.
Interval for sending beacon frames. Beacon frames are transmitted at a regular
interval to allow mobile clients to join the network. Beacon frames are used for
a client to identify nearby APs or network control devices.
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 do 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 do 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 do 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.
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,
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.
Number of beacon intervals between delivery traffic indication message
(DTIM) transmissions. The AP sends buffered broadcast/multicast frames when
the DTIM counter reaches 0.
Number of retransmission attempts for unicast frames larger than the RTS/CTS
threshold.
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