Huawei v200r001 user manual Selecting Congestion Management Policy

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

3.1.3 Selecting Congestion Management Policy

Quidway series routers implement the above four congestion management policies (FIFO, PQ, CQ and WFQ) at the Ethernet port and serial port (PPP, FR and HDLC encapsulation), meeting different QoS demands of different services.

FIFO implements non-priority policy of the packets in user data communication. In this mode, the priority and type of the communication is not necessary to be specified. But in the application of FIFO policy, some data that run abnormally may consume most of the available bandwidth, and occupy the full queue, which will lead to delay of the burst data source and some important communication data being discarded.

PQ provides strict priority. It ensures that a specific type of communication can be sent, but all other types of packets may be sacrificed at this time. In terms of PQ, a queue with lower priority is placed in an unfavorable status. Moreover, the packets in the queues with lower priority may have no chance to be sent out in the worst circumstance (available bandwidth is limited, and the transmission frequency of the emergent communications is very high).

CQ ensures all communications to get service of respective levels by allocating different bandwidths for them. And it determines the queue size by specifying the total number of packets configured in the queue, so as to control the access to the bandwidth.

WFQ dynamically divides the communication into packets by fair queuing algorithm. Packet is one part of the session. WFQ allocates the bandwidths fairly for small- capacity and interactive communications just as large-capacity communications (for example, file transmission).

Comparison for these four policies is shown in the table below:

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