What is the LLQ queue on an AR


A low latency queuing (LLQ) queue is a special EF queue. Compared with EF, LLQ provides shorter delay, which provides good QoS assurance for delay-sensitive services such as VoIP services.
An EF queue has the highest priority. You can put one or more types of packets into EF queues and set different bandwidth for different types of packets.
During packet scheduling, packets in the EF queues are scheduled first to ensure low latency. When traffic is congested on an interface, packets in the EF queues are sent first. To ensure scheduling for low-priority queues (such as AF or BE queues), rate limiting is configured for EF queues. When traffic is not congested on the interface, EF queues can use the idle bandwidth of AF or BE queues. Therefore, packets in EF queues can obtain idle bandwidth, and does not occupy the bandwidth that exceeds the specifications.

Other related questions:
How does an AR send packets with a specific DSCP to high-priority queues

Use traffic classifiers to enable packets with high differentiated services code point (DSCP) values to enter expedited forwarding (EF) queues, and to ensure that the packets are transmitted preferentially. For example, to enable packets with a DSCP of 22 to enter EF queues, configure the following:

[Huawei] traffic classifier c1 [Huawei-classifier-c1] if-match dscp 22 [Huawei-classifier-c1] quit [Huawei] traffic behavior b1 [Huawei-behavior-b1] queue ef bandwidth 100 cbs 2500 [Huawei-behavior-b1] quit [Huawei] traffic policy p1 [Huawei-trafficpolicy-p1] classifier c1 behavior b1

What impact does the queue length have
A longer queue buffers more packets but introduces a longer delay. If congestion intermittently occurs on a network, buffering more packets prevents unnecessary packet loss. If congestion constantly occurs on a network, increasing the queue length cannot solve this problem. You need to increase the bandwidth.

What is the relationship among the Enqueue, Queue pass, and Queue drop Fields in traffic policy statistics (V200R001C00 and V200R001C01)

Queue scheduling mechanism on S series switches
On S series switches (except the S1700), each physical interface has eight transmission queues. Queue 7 has the highest priority whereas Queue 0 has the lowest priority. Transmitting interfaces support PQ, WRR, and DRR scheduling as well as their combinations such as PQ+WRR and PQ+DRR. If PQ+WRR or PQ+DRR scheduling is configured, a switch first schedules packets in PQ queues. During PQ scheduling, the switch first schedules packets in the queue of the highest priority, and then schedules packets in queues of a lower priority. After PQ scheduling is complete, the switch performs WRR or DRR scheduling. When scheduling packets in WRR/DRR queues, the switch first ensures the bandwidth, and then schedules packets in WRR/DRR queues according to their weights. Notes: - X series cards of S series modular switches do not support WRR and PQ+WRR scheduling. - The S5720HI does not support WRR and PQ+WRR scheduling.

What are the mappings between WMM queues and 802.1p priorities
WMM classifies data packets into four queues. 802.1P provides eight priorities. Users can configure the mappings between WMM queues and 802.1p priorities.

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