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QoS Commands, DES-30XX Layer 2 Switch CLI Reference Manual, weight

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DES-30XX Layer 2 Switch CLI Reference Manual 13 QOS COMMANDS The DES-3026 switch supports 802.1p priority queuing. The Switch has 4 priority classes of service. These priority classes of service are numbered from 3 (Class 3) - the highest priority class of service - to 0 (Class 0) - the lowest priority class of service. The eight priority queues specified in IEEE 802.1p (p0 to p7) are mapped to the Switch's priority classes of service as follows: • Priority 0 is assigned to the Switch's Q1 class. • Priority 1 is assigned to the Switch's Q0 class. • Priority 2 is assigned to the Switch's Q0 class. • Priority 3 is assigned to the Switch's Q1 class. • Priority 4 is assigned to the Switch's Q2 class. • Priority 5 is assigned to the Switch's Q2 class. • Priority 6 is assigned to the Switch's Q3 class. • Priority 7 is assigned to the Switch's Q3 class. 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 highest priority class of service are transmitted first. Once a strict scheduling is implemented for QoS, the highest class will work in strict mode and the other classes will remain in a weight fair scheduling mode. 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 which means the switch will consider the highest class of service to have strict scheduling only, while the other queues empty in a round-robin method. See the config scheduling_mechanism command in this section for more information regarding this subject. To use implement round-robin (weighted) priority, the Switch's four priority classes of service can be configured to reduce the buffer in a round-robin fashion - beginning with the highest priority class of service, and proceeding to the lowest priority class of service before returning to the highest priority classes of service. The weighted-priority based scheduling alleviates the main disadvantage of strict priority-based scheduling − in that lower priority class of service get starved of bandwidth − by providing a minimum bandwidth to all classes of service for transmission. This is accomplished by configuring the maximum number of packets allowed to be transmitted from a given priority class of service and the maximum amount of time a given priority class of service 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 classes of service. The possible weight value range is: 1 to 55 packets. The QoS commands in the Command Line Interface (CLI) are listed (along with the appropriate parameters) in the following table. 82

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DES-30XX Layer 2 Switch CLI Reference Manual
82
13
Q
O
S C
OMMANDS
The DES-3026 switch supports 802.1p priority queuing. The Switch has 4 priority classes of service. These priority classes of
service are numbered from 3 (Class 3) — the highest priority class of service — to 0 (Class 0) — the lowest priority class of
service. The eight priority queues specified in IEEE 802.1p (p0 to p7) are mapped to the Switch’s priority classes of service as
follows:
•
Priority 0 is assigned to the Switch’s Q1 class.
•
Priority 1 is assigned to the Switch’s Q0 class.
•
Priority 2 is assigned to the Switch’s Q0 class.
•
Priority 3 is assigned to the Switch’s Q1 class.
•
Priority 4 is assigned to the Switch’s Q2 class.
•
Priority 5 is assigned to the Switch’s Q2 class.
•
Priority 6 is assigned to the Switch’s Q3 class.
•
Priority 7 is assigned to the Switch’s Q3 class.
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 highest priority class of service are transmitted first. Once a strict
scheduling is implemented for QoS, the highest class will work in strict mode and the other classes will remain in a weight fair
scheduling mode. 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 which means
the switch will consider the highest class of service to have strict scheduling only, while the
other queues empty in a round-robin method. See the
config scheduling_mechanism
command in this section for more information regarding this subject.
To use implement round-robin (weighted) priority, the Switch’s four priority classes of service can be configured to reduce the
buffer in a round-robin fashion - beginning with the highest priority class of service, and proceeding to the lowest priority class
of service before returning to the highest priority classes of service.
The weighted-priority based scheduling alleviates the main disadvantage of strict priority-based scheduling
−
in that lower
priority class of service get starved of bandwidth
−
by providing a minimum bandwidth to all classes of service for transmission.
This is accomplished by configuring the maximum number of packets allowed to be transmitted from a given priority class of
service and the maximum amount of time a given priority class of service 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 classes of
service.
The possible
weight
value range is: 1 to 55 packets.
The QoS commands in the Command Line Interface (CLI) are listed (along with the appropriate parameters) in the following
table.