User`s guide

DES-3226S Layer 2 Switch CLI Reference
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QOS COMMANDS
The DES-3226S 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 using
the config scheduling command. See config
scheduling below.