Extreme Networks ExtremeWare XOS 11.3, Manual

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Quality of Service
ExtremeWare XOS 11.3 Concepts Guide
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strict priority, which is the default, or weighted round robin. In the strict priority method, the switch
services the higher-priority queues first. As long as a queued packet remains in a higher-priority queue,
any lower-priority queues are not serviced. If you configure the switch for weighted-round-robin
scheduling, the system services all queues based on the weight assigned to the QoS profile. The
hardware services higher-weighted queues more frequently, but lower-weighted queues continue to be
serviced at all times.
When configured to do so, the priority of a QoS profile can determine the 802.1p bits used in the
priority field of a transmitted packet (see
“Replacing 802.1p priority information” on page 299 ). The
priority of a QoS profile determines the DiffServ code point value used in an IP packet when the packet
is transmitted (see
“Replacing DiffServ code points” on page 301 ).
A QoS profile switch does not alter the behavior of the switch until it is assigned to a traffic grouping.
The default QoS profiles cannot be deleted. The settings for the default QoS parameters on the
BlackDiamond 8800 family of switches and the Summit X450 switch are summarized in
Table 41 .
QoS Profiles on the BlackDiamond 10K Switch
The BlackDiamond 10K switch has 8 hardware queues for each egress port. The QoS profiles, QP1 to
QP8, map to these hardware queues.
A QoS profile on the BlackDiamond 10K switch defines a class of service by specifying traffic behavior
attributes, such as bandwidth. The parameters that make up a QoS profile on the BlackDiamond 10K
switch include:
●
Minimum bandwidth—The minimum total link bandwidth that is reserved for use by a hardware
queue on a physical port (each physical port has eight hardware queues, corresponding to a QoS
profile). The minimum bandwidth value is configured either as a percentage of the total link
bandwidth or using absolute committed rates in Kbps or Mbps. Bandwidth unused by the queue can
be used by other queues. The minimum bandwidth for all queues should add up to less than 100%.
The default value on all minimum bandwidth parameters is 0%.
●
Maximum bandwidth—The maximum total link bandwidth that can be transmitted by a hardware
queue on a physical port (each physical port has eight hardware queues, corresponding to a QoS
profile). The maximum bandwidth value is configured either as a percentage of the total link
bandwidth or using absolute peak rates in Kbps or Mbps. The default value on all maximum
bandwidth parameters is 100%.
●
Priority—The level of priority assigned to a hardware egress queue on a physical port. There are
eight different available priority settings and eight different hardware queues. By default, each of the
default QoS profiles is assigned a unique priority. You use prioritization when two or more hardware
queues on the same physical port are contending for transmission on the same physical port, only
after their respective bandwidth management parameters have been satisfied. If two hardware
queues on the same physical port have the same priority, a round-robin algorithm is used for
transmission, depending on the available link bandwidth.
■
When configured to do so, the priority of a QoS profile can determine the 802.1p bits used in the
priority field of a transmitted packet (see
“Replacing 802.1p priority information” on page 299 ).
Table 41: Default QoS profile parameters on the BlackDiamond 8800 family of switches and the
Summit X450 switch
Profile name Priority Buffer Weight
QP1 Low 100% 1
QP8 High 100% 1