D-Link DES-3326SR Layer 3 Switch
Chapter 10
Quality of Service Configuration
Configure QoS Output Scheduling
Configure 802.1p User Priority
Configure Default Priority
Configure Bandwidth
The DES-3326SR switch supports 802.1p priority queuing. The switch has 4 priority queues. These priority
queues are numbered from 0 (Class 0) — the lowest priority queue — to 3 (Class 3) — the highest priority
queue. The eight priority queues specified in IEEE 802.1p (p0 to p7) are mapped to the switch’s priority queues
as follows:
p1 and p2 are assigned to the switch’s Class 0 queue.
p0 and p3 are assigned to the switch’s Class 1 queue.
p4 and p5 are assigned to the switch’s Class 2 queue.
p6 and p7 are assigned to the switch’s Class 3 queue.
Priority scheduling is implemented using two types of methods, strict priority and round-robin priority. If no
changes are made to the QoS priority scheduling settings the method used is strict priority.
For strict priority-based scheduling, packets residing in the higher priority queues are transmitted first. Only
when these queues are empty, are packets of lower priority allowed to be transmitted. Higher priority packets
always receive preference regardless of the amount of lower priority packets in the buffer and regardless of the
time elapsed since any lower priority packets have been transmitted. By default the switch is configured to
empty the buffer using strict priority.
NOTICE:
The default QoS scheduling arrangement is a strict priority schedule. To
customize scheduling to set up round-robin queue clearing, the MAX. Latency and
MAX. Packets values need to be changed.
To use implement round-robin (weighted) priority, the switch’s four priority queues can be configured to reduce
the buffer in a round-robin fashion - beginning with the highest priority queue, and proceeding to the lowest
priority queue before returning to the highest priority queue.
The weighted-priority based scheduling alleviates the main disadvantage of strict priority-based scheduling
−
in
that lower priority queues get starved of bandwidth
−
by providing a minimum bandwidth to all queues for
transmission. This is accomplished by configuring the maximum number of packets allowed to be transmitted
from a given priority queue and the maximum amount of time a given priority queue will have to wait before
being allowed to transmit its accumulated packets. This establishes a Class of Service (CoS) for each of the
switch’s four hardware priority queues.
The possible range for maximum packets is: 0 to 255 packets.
The possible range for maximum latency is: 0 to 255 (in increments of 16 microseconds each).
Remember that the DES-3326SR has four priority queues (and thus four Classes of Service) for each port on the
switc
To configure QoS settings, open the
Configure QoS
subdirectory in the
Advanced Setup
folder, and the click
on the link for the QoS setting you want to configure. h.
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