Port Scheduler Method - D-Link DGS-1250 Series Reference Manual

DGS-1250 Series Gigabit Ethernet Smart Managed Switch Web UI Reference Guide

Port Scheduler Method

This window is used to display and configure the port scheduler method settings.
To view the following window, click QoS > Basic Settings > Port Scheduler Method, as shown below:
The fields that can be configured are described below:
Parameter
From Port - To Port
Scheduler Method
Figure 7-2 Port Scheduler Method Window
Description
Select the range of ports that will be used for this configuration here.
Select the scheduler method that will be applied to the specified port(s). Options
to choose from are Strict Priority (SP), Round-Robin (RR), Weighted Round-Robin
(WRR), and Weighted Deficit Round-Robin (WDRR). By default, the output queue
scheduling algorithm is WRR.
• Strict Priority (SP) specifies that all queues use strict priority scheduling. It
provides strict priority access to the queues from the highest CoS queue to
the lowest.
• Round-Robin (RR) specifies that all queues use round-robin scheduling. It
provides fair access to service a single packet at each queue before moving
on to the next one.
• Weighted Round-Robin (WRR) operates by transmitting permitted packets
into the transmit queue in a round robin order. Initially, each queue sets its
weight to a configurable weighting. Every time a packet from a higher priority
CoS queue is sent, the corresponding weight is subtracted by 1 and the
packet in the next lower CoS queue will be serviced. When the weight of a
CoS queue reaches zero, the queue will not be serviced until its weight is
replenished. When weights of all CoS queues reach 0, the weights get
replenished at a time.
• Weighted Deficit Round-Robin (WDRR) operates by serving an
accumulated set of backlogged credits in the transmit queue in a round robin
order. Initially, each queue sets its credit counter to a configurable quantum
value. Every time a packet from a CoS queue is sent, the size of the packet
is subtracted from the corresponding credit counter and the service right is
turned over to the next lower CoS queue. When the credit counter drops
below 0, the queue is no longer serviced until its credits are replenished.
When the credit counters of all CoS queues reaches 0, the credit counters
will be replenished at that time. All packets are serviced until their credit
counter is zero or negative and the last packet is transmitted completely.
When this condition happens, the credits are replenished. When the credits
are replenished, a quantum of credits are added to each CoS queue credit
counter. The quantum for each CoS queue may be different based on the
user configuration.
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