User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform Chapter 3
Congestion Management
3-3
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 neces sary to be specified. But
in the application of FIFO policy, some data that run abnormally ma y 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 tim e. In term s 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 circ umstance
(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 b y 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 queu ing algorithm.
Packet is one part of the session. WFQ allocates the bandwidths fairly for sm all-
capacity and interactive communications just as large-capacit y communications (for
example, file transmission).
Comparison for these four policies is shown in the table below: