D-Link DI-3660 [377/506] Qos queueing algorithms

D-Link DI-3660 [377/506] Qos queueing algorithms
Command Line Interface Reference Manual
377
The QoS provides Weighted Random Early Detection (WRED), Custom Queueing (CQ), and Priority Queueing (PQ) to
deliver differentiated services.
7.1.3 QoS Queueing Algorithms
QoS Queueing Algorithms are the important guarantee to achieve QoS configuration. D-LINK router supports Weighted
Fair Queueing (WFQ), Custom Queueing (CQ), Priority Queueing (PQ), Weighted Random Early Detection (WRED),
and the simplest first-in and first-out (FIFO) algorithm.
7.1.3.1 Weighted Fair Queueing
WFQ is a dynamic scheduling method that provides fair bandwidth allocation to all network traffic. WFQ applies priority,
or weights, to identified traffic to classify traffic into conversations and determine how much bandwidth each
conversation is allowed relative to other conversations. WFQ is a flow-based algorithm that simultaneously schedules
interactive traffic to the front of a queue to reduce response time and fairly shares the remaining bandwidth among
high-bandwidth flows. In other words, WFQ allows you to give low-volume traffic, such as Telnet sessions, priority over
high-volume traffic, such as FTP sessions. WFQ gives concurrent file transfers balanced use of link capacity; that is, when
multiple file transfers occur, the transfers are given comparable bandwidth.
WFQ overcomes a serious limitation of FIFO queueing. When FIFO is in effect, traffic is sent in the order received
without regard for bandwidth consumption or the associated delays. As a result, file transfers and other high-volume
network applications often generate series of packets of associated data and depriving other traffic of bandwidth. WFQ
provides traffic priority management that dynamically sorts traffic into messages that make up a conversation to ensure
that bandwidth is shared fairly between individual conversations and that low-volume traffic is transferred in a timely
fashion.
WFQ classifies traffic into different flows based on packet header addressing. For most of traffic are IP data, thus the
WFQ classifies the data packets based on characteristics of IP header, including such characteristics as source and
destination address, source and destination port, protocol types, and ToS value.
WFQ places packets of the various conversations in the fair queues before transmission. The order of removal from the
fair queues is determined by the virtual time of the delivery of the last bit of each arriving packet (finish number).
Flow-based WFQ is used as the default queueing mode on most serial interfaces configured to run at E1 speeds (2.048
Mbps) or below.
See the WFQ Configuration for particular configuration of WFQ.
WFQ is only automatically identify flow but does not offer the special service for some peculiar flow. D-Link router
provides Class-Based Weighted Fair Queueing (CBWFQ), which enhanced the standard WFQ. It can identifies the type of
flow by user customization and distribute the authority to the flow.
See the CBWFQ Configuration for particular configuration of CBWFQ.
7.1.3.2 Weighted Random Early Detection
Random Early Detection (RED) is a common congestion avoidance mechanism. Random Early Detection (RED) is a
congestion avoidance mechanism that takes advantage of TCP's congestion control mechanism. By randomly dropping
packets prior to periods of high congestion, RED tells the packet source to decrease its transmission rate. Assuming the
packet source is using TCP, it will decrease its transmission rate until all the packets reach their destination, indicating that
the congestion is cleared.

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