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To use a high-priority access category, a client must send a request to the AP. The AP returns a positive
or negative response based on either of the following admission control policy:
• Channel utilization-based admission policy—The AP calculates the total time that the existing
high-priority access categories occupy the channel in one second, and then calculates the time that
the requesting traffic will occupy the channel in one second. If the sum of the two values is smaller
than or equal to the maximum hold time of the channel, the client can use the requested access
category. Otherwise, the request is rejected.
• Users-based admission policy—If the number of clients using high-priority access categories plus
the requesting clients is smaller than or equal to the maximum number of high-priority access
category clients, the request is accepted. Otherwise, the request is rejected. During calculation, a
client is counted once even if it is using both AC-VO and AC-VI.
U-APSD power-save mechanism
U-APSD improves the 802.11 APSD power saving mechanism. When associating clients with access
categories, specify some access categories as trigger-enabled, some access categories as
delivery-enabled, and the maximum number of data packets that can be delivered after receiving a
trigger packet. Both the trigger attribute and the delivery attribute can be modified when flows are
established using CAC. When a client sleeps, the delivery-enabled access category packets destined for
the client are buffered. The client needs to send a trigger-enabled access category packet to get the
buffered packets. After the AP receives the trigger packet, packets in the transmit queue are sent. The
number of sent packets depends on the agreement made when the client was admitted. Access
categories without the delivery attribute store and transmit packets as defined in the 802.11 protocol.
SVP service
SVP service implements differentiated treatment of SVP packets by mapping each SVP packet (IP protocol
number 119) to an access category, which corresponds to a transmit queue with certain priority.
ACK policy
WMM defines two ACK policies:
• No ACK—When the no acknowledgement (No ACK) policy is used, the recipient does not
acknowledge received packets during wireless packet exchange. This policy can improve
transmission efficiency in the environment where communication quality is fine and interference is
weak. However, in the environment where communication quality is poor, it can cause increased
packet loss and deteriorated communication quality.
• Normal ACK—When the Normal ACK policy is used, the recipient acknowledges each received
unicast packet.
Enabling wireless QoS
1. Select QoS > Wireless QoS from the navigation tree.
By default, the QoS Service tab is displayed.
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