DXS-3326GSR Stackable Gigabit Layer 3 Switch
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QOS COMMANDS
The DXS-3326GSR switch supports 802.1p priority queuing. The Switch has eight hardware priority queues, one of which is
internal and unconfigurable. These hardware priority queues are numbered from 6 (Class 6) — the highest hardware priority
queue — to 0 (Class 0) — the lowest hardware priority queue. The eight priority tags specified in IEEE 802.1p (p0 to p7) are
mapped to the Switch’s hardware priority queues as follows:
• Priority 0 is assigned to the Switch’s Q2 queue.
• Priority 1 is assigned to the Switch’s Q0 queue.
• Priority 2 is assigned to the Switch’s Q1 queue.
• Priority 3 is assigned to the Switch’s Q3 queue.
• Priority 4 is assigned to the Switch’s Q4 queue.
• Priority 5 is assigned to the Switch’s Q5 queue.
• Priority 6 is assigned to the Switch’s Q6 queue.
• Priority 7 is assigned to the Switch’s Q6 queue.
Priority scheduling is implemented using two types of methods, strict priority and weight fair 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 hardware priority queues are transmitted first. Only when
these queues are empty, are packets of lower hardware priority allowed to be transmitted. Higher priority tagged packets always
receive precedence regardless of the amount of lower priority tagged packets in the buffer and regardless of the time elapsed
since any lower priority tagged 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
weight fair queue clearing, the MAX. Packets values need to
be changed using the config scheduling command. See
config scheduling below.
To use implement weight fair priority, the Switch’s seven hardware priority queues can be configured to reduce the buffer in a
weighted round-robin (WRR) fashion - beginning with the highest hardware priority queue, and proceeding to the lowest
hardware priority queue before returning to the highest hardware 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 eight hardware priority queues.
The possible range for maximum packets is: 0 to 15 packets.
The commands in the Command Line Interface (CLI) are listed (along with the appropriate parameters) in the following table.
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