Huawei v200r001 user manual Fifo Queuing, II. PQ Priority Queuing, III. CQ Custom Queuing

User Manual - Configuration Guide (Volume 3)	Chapter 3
Versatile Routing Platform	Congestion Management

resend the data packets due to timeout, and congestion happens again, and then the packets are sent again, a vicious circle happens. To manage the congestion of network, people adopt some policies. When congestion occurs, the router can adopt a specific policy to dispatch the data packets, and decide which packets to be sent with priority, and which packets to be discarded. The policy adopted by the router to deal with congestion is called congestion management policy. Usually Queuing technology is adopted to manage the congestion. When congestion occurs, data packets queue up at the sending interface of the router following a certain policy. When the packets are dispatched, the sending sequence of the packets is determined following a certain policy.

I. FIFO Queuing

In FIFO (First-In First-Out) queuing, communication priority and classification is not concerned. In FIFO application, the sequence of sending out data packets from the interface depends on the arriving sequence of the data packets at this interface.

FIFO provides basic capability of storage and forwarding. In some cases, FIFO is the default queuing algorithm, which should not be modified.

II. PQ (Priority Queuing)

In PQ (Priority Queuing), packets with a specific communication priority will be forwarded earlier than all other packets with lower priorities, thus ensuring that the packets with higher priority can be sent out in time.

PQ is used to provide strict priority for important network data. PQ can flexibly specify priority sequence according to network protocol (IP protocol for example), data inflow interface, length of the packet, source address/destination address, etc. It ensures that the most important data in the network unit using PQ can be processed as fast as possible.

III. CQ (Custom Queuing)

In CQ (Custom Queuing), a specific proportion of the available bandwidth of the interface is reserved for each specified traffic type. When the reserved bandwidth is not used by its type of traffic, it can be used by other types of traffic. That is, in CQ mode, bandwidth is allocated in proportion, and CQ permits to specify the total number of byte/packet to be extracted from the queue.

For interfaces with a low rate, the data flow passing through this interface can also receive network service to some extent when the queue is customized for the interface.

IV. WFQ (Weighted Fair Queuing)

WFQ (Weighted Fair Queuing) provides a dynamic and fair queuing mode, in which the traffic is distinguished based on priority/weight, and according to the different sessions. The occupation of bandwidth is determined for each session, thus ensuring a fair treatment to all communications according to their weight. The traffic is classified by WFQ in the light of source address, destination address, source port number, destination port number and protocol type, etc.

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