Cisco Systems EA6500 Manual De Usuario

1p1q0t indicates one strict-priority queue and one standard queue with no configurable threshold 
(effectively a tail-drop threshold at 100 percent). 

1p1q8t indicates one strict-priority queue and one standard queue with eight thresholds, each 
configurable as either WRED-drop or tail-drop, and one non-configurable (100 percent) tail-drop 
threshold.

Strict-priority queues are queues that are serviced in preference to other queues. PFC QoS services 
traffic in a strict-priority queue before servicing the standard queue. When PFC QoS services the 
standard queue, after receiving a packet, it checks for traffic in the strict-priority queue. If PFC QoS 
detects traffic in the strict-priority queue, it suspends its service of the standard queue and completes 
service of all traffic in the strict-priority queue before returning to the standard queue.

PFC QoS schedules traffic through the receive queues based on Layer 2 CoS values. In the 1p1q4t, 
1p1q0t and 1p1q8t default configurations, PFC QoS assigns all traffic with CoS 5 to the strict-priority 
queue; PFC QoS assigns all other traffic to the standard queue. In the 1q4t default configuration, PFC 
QoS assigns all traffic to the standard queue.

If an ingress LAN port is configured to trust CoS, PFC QoS implements Layer 2 CoS-value-based 
receive-queue drop thresholds to avoid congestion in received traffic.

1q2t ingress LAN ports have this default drop-threshold configuration: 

Frames with CoS 0, 1, 2, 3, or 4 go to tail-drop threshold 1, where the switch drops incoming frames 
when the standard receive-queue buffer is 80 percent full. 

Frames with CoS 5, 6, or 7 go to tail-drop threshold 2, where the switch drops incoming frames when 
the standard receive-queue buffer is 100 percent full. 

1q4t ingress LAN ports have this default drop-threshold configuration:

Using receive-queue tail-drop threshold 1, the switch drops incoming frames with CoS 0 or 1 when 
the receive-queue buffer is 50 percent or more full.

Using receive-queue tail-drop threshold 2, the switch drops incoming frames with CoS 2 or 3 when 
the receive-queue buffer is 60 percent or more full.

Using receive-queue tail-drop threshold 3, the switch drops incoming frames with CoS 4 or 5 when 
the receive-queue buffer is 80 percent or more full.

Using receive-queue tail-drop threshold 4, the switch drops incoming frames with CoS 6 or 7 when 
the receive-queue buffer is 100 percent full.

1p1q4t ingress LAN ports have this default drop-threshold configuration:

Frames with CoS 5 go to the strict-priority receive queue (queue 2), where the switch drops 
incoming frames only when the strict-priority receive-queue buffer is 100 percent full.

Frames with CoS 0, 1, 2, 3, 4, 6, or 7 go to the standard receive queue.

Using standard receive-queue tail-drop threshold 1, the switch drops incoming frames with 
CoS 0 or 1 when the receive-queue buffer is 50 percent or more full.

Using standard receive-queue tail-drop threshold 2, the switch drops incoming frames with 
CoS 2 or 3 when the receive-queue buffer is 60 percent or more full.