H3C Technologies H3C MSR 50 - Manual (Page 74)

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high-priority AC queue clients, the request is accepted. Otherwise, the request is rejected. During
calculation, a client is counted once even if it is using both the AC-VO and AC-VI queues.
U-APSD power-save mechanism
U-APSD improves the 802.11 APSD power saving mechanism. When associating clients with AC queues,
you can specify some AC queues as trigger-enabled, some AC queues 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 AC queue packets destined for the client are buffered. The client must
send a trigger-enabled AC queue 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. AC queues without the delivery attribute store and transmit packets
as defined in the 802.11 protocol.
SVP
SVP can assign packets with the protocol ID 119 in the IP header to a specific AC queue. SVP stipulates
that random backoff is not performed for SVP packets. Therefore, you can set both ECWmin and
ECWmax to 0 when there are only SVP packets in an AC queue.
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 is suitable in the
environment where communication quality is fine and interference is weak. While the No ACK
policy helps improve transmission efficiency, it can cause increased packet loss when
communication quality deteriorates. This is because when this policy is used, a sender does not
retransmit packets that have not been received by the recipient.
• Normal ACK—When the Normal ACK policy is used, the recipient acknowledges each received
unicast packet.
Protocols and standards
• 802.11e-2005, Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements,
IEEE Computer Society, 2005
• Wi-Fi, WMM Specification version 1.1, Wi-Fi Alliance, 2005
Configuring WMM
Configuration restrictions and guidelines
• If CAC is enabled for an AC queue, CAC is also enabled for the AC queues with higher priority. For
example, if you use the wmm edca client command to enable CAC for the AC-VI queue, CAC is
also enabled for the AC-VO queue. However, enabling CAC for the AC-VO queue does not enable
CAC for the AC-VI queue.
• H3C recommends that you use the default EDCA parameter settings for APs and clients (except the
TXOPLimit parameter for devices using 802.11b radio cards) unless it is necessary to modify the
default settings.