Signamax Managed Hardened PoE Industrial DIN-rail Mount Switch - Manual (Page 31)

6 QoS
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Port-based Priority：There is 8 priorities from 0 to 7.
DSCP：Enable or disable DSCP
The lower part of QoS Configuration tab page lists the default priority of all ports and the state
of DSCP.
6.2 Scheduling Mechanism
This page sets the queue scheduling algorithm and related parameters.
Scheduling Mechanism: Can be set to Strict Priority or Weighted Round-Robin (WRR)
Strict Priority: SP queue-scheduling algorithm is specially designed for critical service
applications. An important feature of critical services is that they demand preferential service
in congestion in order to reduce the response delay. Assume that there are eight output
queues on the port and the preferential queue classifies the eight output queues on the port
into eight classes, which are queue 7, queue 6, queue 5, queue 4, queue 3, queue 2, queue 1,
and queue 0. Their priorities decrease in order.
In queue scheduling, SP sends packets in the queue with higher priority strictly following the
priority order from high to low. When the queue with higher priority is empty, packets in the
queue with lower priority are sent. You can put critical service packets into the queues with
higher priority and put non-critical service (such as e-mail) packets into the queues with lower
priority. In this case, critical service packets are sent preferentially and non-critical service
packets are sent after critical service groups are sent.
The disadvantage of SP queue is that: if there are packets in the queues with higher priority
for a long time in congestion, the packets in the queues with lower priority will be “starved”
because they are not served.
Weighted Round-Robin (WRR) (8:4:2:1): WRR queue-scheduling algorithm schedules all
the queues in turn and every queue can be assured of a certain service time. Assume there
are four priority queues on a port. WRR configures a weight value for each queue, which are
Q1, Q2, Q3 and Q4. The weight value indicates the proportion of obtaining resources. On a
150 M port, configure the weight value of WRR queue-scheduling algorithm to 8, 4, 2 and 1
(corresponding to Q1, Q2, Q3 and Q4 in order). In this way, the queue with the lowest priority
can get 10 Mbps bandwidth at least, and the disadvantage of SP queue-scheduling that the
packets in queues with lower priority may not get service for a long time is avoided. Another