Cbq - HP FlexNetwork MSR Series Configuration Manuals

When dequeuing packets, WFQ assigns the outgoing interface bandwidth to each traffic flow by
precedence. The higher precedence value a traffic flow has, the more bandwidth it gets.
For example, five flows exist in the current interface with precedence 0, 1, 2, 3, and 4, respectively.
The total bandwidth quota is the sum of all the (precedence value + 1)s, 1 + 2 + 3 + 4 + 5 = 15.
The bandwidth percentage assigned to each flow is (precedence value of the flow + 1)/total
bandwidth quota. The bandwidth percentages for flows are 1/15, 2/15, 3/15, 4/15, and 5/15,
respectively.
Because WFQ can balance the delay and jitter of each flow when congestion occurs, it is suitable for
handling special situations. For example, WFQ is used in the assured forwarding (AF) services of the
RSVP, and WFQ is used to schedule buffered packets in GTS.
Figure 18 Weighted fair queuing (WFQ)
Packets to be sent
through this interface

CBQ

Class-based queuing (CBQ) extends WFQ by supporting user-defined classes. When network
congestion occurs, CBQ uses user-defined traffic match criteria to enqueue packets. Before packets
are enqueued, congestion avoidance actions, such as tail drop or WRED and bandwidth restriction
check, are performed. When being dequeued, packets are scheduled by WFQ.
CBQ provides the following queues:
•
Emergency queue—Enqueues emergent packets. The emergency queue is a FIFO queue
without bandwidth restriction.
•
Strict priority (SP) queuing—SP queuing is designed for mission-critical applications.
Mission-critical applications require preferential treatment to reduce the response delay when
congestion occurs. With SP queuing, CBQ can provide strict priority service. A maximum of 64
SP queues are supported.
•
Low Latency Queuing (LLQ)—An EF queue. Because packets are fairly treated in CBQ,
delay-sensitive flows like video and voice packets might not be transmitted timely. To solve this
problem, LLQ combines PQ and CBQ to preferentially transmit delay-sensitive flows like voice
packets. When defining traffic classes for LLQ, you can configure a class of packets to be
preferentially transmitted. The packets of all priority classes are assigned to the same priority
queue. Bandwidth restriction on each class of packets is checked before the packets are
enqueued. During the dequeuing operation, packets in the priority queue are transmitted first.
To reduce the delay of the other queues except the priority queue, LLQ assigns the maximum
available bandwidth to each priority class. The bandwidth value polices traffic during
congestion. When no congestion is present, a priority class can use more than the bandwidth
Queue 1 weight 1
Queue 2 weight 2
......
Queue N-1 weight N-1
Classify
Queue N weight N
Packets sent
Schedule Sending queue
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Interface