User guide

9-6 E
XTREME
W
ARE
S
OFTWARE
U
SER
G
UIDE
Q
UALITY OF
S
ERVICE
(Q
O
S)
Q
O
S P
ROFILES
A QoS profile defines a class of service by specifying traffic behavior attributes, such as
bandwidth. The parameters that make up a QoS profile include the following:
• Minimum bandwidth – The minimum percentage of total link bandwidth that
reserved for use by a hardware queue on a physical port. Bandwidth unused by the
queue can be used by other queues. The minimum bandwidth for all queues should
add up to less than 90%. The default value on all minimum bandwidth parameters is
0%.
• Maximum bandwidth – The maximum percentage of total link bandwidth that may
be transmitted by a hardware queue on a physical port. The default value on all
maximum bandwidth parameters is 100%.
• Priority – The level of priority assigned to a hardware queue on a physical port.
Switch products that use the “i” chipset have eight different available priority
settings. Other Extreme switches have four available priority settings. By default,
each of the default QoS profiles is assigned a unique priority. You would 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 may determine the 802.1p
bits used in the priority field of a transmitted packet (described later).
— On switch products using the “i” chipset, the priority of a QoS profile determines
the DiffServ code point value used in an IP packet when the packet is transmitted
(described later).
• Buffer – This parameter reserves buffer memory for use exclusively by a QoS profile
across all affected ports. The default value for buffer settings is 0%. The sumvalue of
all QoS profile buffer parameters should not exceed 100%. Reserving buffer memory
for a QoS profile affects the dynamic buffer space available to other QoS profiles.
You should not modify the buffer parameter unless specific situations and
application behavior indicate.
A QoS profile does not alter the behavior of the switch until it is assigned to a traffic
grouping. Recall that QoS profiles are linked to hardware queues. There are multiple
hardware queues per physical port. By default, a QoS profile links to the identical
hardware queue across all the physical ports of the switch.