Alcatel-Lucent 7750 Configuration Manual page 554

Interfaces
provisioning, this prevents a seldom active queue from being denied a buffer from the mega-pool when the
shared portion of the mega-pool is congested. Further control over shared congestion is defined later in this
document under the slope-policy command.
The WRED mega-slope reserve CBS size is controlled in the same manner as the overall sizing of the
WRED mega-pool. A min and max parameter is provided to scope the range that the reserved portion based
on percentages of the WRED mega-pool current size. Forwarding class cbs-factor settings are used in the
same way as the mbs-factor parameters to move the actual reserved size between the minimum and maxi-
mum thresholds according to appropriate oversubscription factors that are applied to the sum of the WRED
queue CBS values.
When min and max are defined as the same value, the WRED mega-pool size will not fluctuate and the
oversubscription factors will have no effect.
FC CBS Oversubscription Factors and WRED CBS Reserve Sizing
Each WRED queue in a SAP egress QoS policy is created on an egress IOM3-XP when the policy is applied
to an egress SAP on the IOM and at least one forwarding class is mapped to the queue. For WRED queue
CBS buffer management purposes, each forwarding class is configured with a CBS oversubscription factor
(OSF) on the IOM using the osf command. The CBS oversubscription factor is used by the system as a pro-
visioning parameter that defines the acceptable level of oversubscription between the sum of the committed
buffer sizes (CBS) of the WRED queues for a given class and the number of buffers for that class that should
be placed in the WRED mega-pool CBS reserve. Since multiple forwarding classes may be mapped to the
same queue, the oversubscription factor associated with the highest forwarding class mapped is used for
dynamically sizing the WRED mega-pool CBS reserve.
As an example, when a WRED queue is configured with the following attributes:
•
•
And the forwarding plane on theIOM3-XP is configured with the following WRED limits:
•
•
The system will increase the WRED mega-pool CBS reserve size to 103Kbytes (increase of 6Kbytes/2) as
long as the maximum buffer allocation percentage for resv-cbs equates to a value equal to or greater than
103Kbytes. (If not, the WRED mega-pool CBS reserve will be capped at the maximum level.)
The no form of the command immediately restores the default min and max percentage values for sizing the
WRED mega-pool CBS reserve.
Parameters min percent-of-total — This required keyword defines the minimum percentage of the IOM3-XP WRED
mega-pool buffers that will be applied to the CBS reserve. The value given for percent-of-wred must be
less than or equal to the value given for the max percent-of-wred. Percentages are defined with an accu-
racy of hundredths of a percent in the nn.nn format (15.65 = 15.65%).
Values
Default
max percent-of-total — This required keyword defines the maximum percentage of the IOM3-XP WRED
mega-pool buffers that may be applied to the CBS reserve. The value given for percent-of-wred must be
greater than or equal to the value given for the min percent-of-wred. Percentages are defined with an
Page 554
CBS equal to 6Kbytes
AF as the highest forwarding class mapped
Current WRED mega-pool CBS reserve is sized at 100Kbytes
AF CBS oversubscription factor is 2 (2:1)
0.00 — 99.99
25.00
7750 SR Interface Configuration Guide