| WFQ
is an automated method that provides fair bandwidth allocation to
all network traffic; it provides traffic-priority management that
dynamically sorts traffic into messages that make up a conversation.
WFQ then breaks up the “train” of packets within each
conversation to ensure that the bandwidth is shared fairly between
individual conversations.
WFQ overcomes an important limitation of FIFO
queuing--WFQ breaks up packet trains to ensure that low-volume
traffic is transferred in a timely fashion. This protocol gives
low-volume traffic, such as Telnet sessions, priority over
high-volume traffic, such as File Transfer Protocol (FTP) sessions. WFQ gives concurrent file transfers balanced use of link capacity.
Fair queuing is enabled by default for
physical interfaces with bandwidth less than or
equal to 2.048 Mbps that do not use Link Access Procedure, Balanced
(LAPB), X.25, compressed Point-to-Point Protocol (PPP), or Synchronous Data Link Control (SDLC) encapsulations. Fair queuing is
not an option for these protocols.
The WFQ algorithm arranges traffic into
conversations. The discrimination of traffic into conversations is
based on packet-header addressing.
Common conversation discriminators include:
- Source/destination network address
- Source/destination Media Access
Control (MAC) address
- Source/destination port or socket
numbers
- Frame Relay data-link connection
identifier (DLCI) value
- Quality of service/type of service
(QoS/ToS) value
In the Figure,
the WFQ algorithm has identified three conversations.
The WFQ algorithm places packets of the
various conversations in the fair queue before transmission. The
order of removal from the fair queue is determined by the virtual
delivery time of the last bit of each arriving packet. Small,
low-volume packets are given priority over large, high-volume
conversation packets.
In the Figure, packet 3 is queued
before packets 1 or 2 because packet 3 is a small packet in a
low-volume conversation. As a result of the queuing order, short
messages, (ones that do not require much bandwidth), are given
priority.
After low-volume conversations are
serviced, high-volume conversations share the remaining link
capacity fairly, and interleave (alternate) transmission timeslots.
In this Figure, high-volume conversation packets are queued in order
of arrival after the low-volume packet--packets 1 and 2 transmit in
the order received.
The queuing algorithm ensures the
proper amount of bandwidth for each message. With WFQ, two
equal-size file transfers get equal bandwidth, rather than the first
file transfer using most of the link's capacity.
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