Alcatel-Lucent 7750 Configuration Manual page 552

Interfaces
wred-queue-control
Syntax wred-queue-control
Context config>card>fp>egress
Description
This command enables the context to configure the aggregate WRED queue parameters for all WRED
queues on an egress IOM3-XP forwarding plane.
buffer-allocation
Syntax buffer-allocation min percentage max percentage
no buffer-allocation
Context config>card>fp>egress>max-wred-control
Description The buffer-allocation command defines the amount of IOM3-XP buffers that will be set aside for WRED
queue buffer pools. Note that the min percentage and max percentage parameters must be set to the same
value. The IOM3-XP protects against cross application buffer starvation by implementing a hierarchy of
buffer pools. At the top of the hierarchy are mega-pools. Mega-pools are used to manage buffers at a system
application level. Two mega-pools are currently used by the system. The first (default) mega-pool services
all non-WRED type queues and when WRED queues are not enabled will contain all available forwarding
plane queue buffers. When WRED queuing is enabled, the second mega-pool (the WRED mega-pool) is
given buffers from the default mega-pool based on the buffer-allocation command and the size if further
fine-tuned by the forwarding class oversubscription factors.
The mega-pools provide buffers to the second tier buffer pools. The default mega-pool services all default
pools and explicitly created named pools. As the name implies, the WRED mega-pool services all the
WRED buffer pools created for the WRED queues. The WRED mega-pool allows each WRED queue pool
to be configured to an appropriate size while allowing the sum of the WRED queue pool sizes to oversub-
scribe the total amount set aside for WRED queue buffering without affecting the queues using the default or
named pools. Further oversubscription controls are described within the resv-cbs command later in this doc-
ument.
The WRED mega-pool is allowed to expand between the min and max percent of total forwarding plane buf-
fers based on the sum of the WRED queue sizes and the WRED oversubscription factors. As the WRED
mega-pool grows, the number of buffers available to the default mega-pool will shrink. If the WRED mega-
pool shrinks, the default mega-pool will grow accordingly. 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.
No buffers are allocated to the WRED mega-pool until the wred-queue-control shutdown command is set to
no shutdown. When the shutdown command is executed, all buffers allocated to the WRED mega-pool are
returned to the default mega-pool and all WRED queues are returned either to their default buffer pool or
their specified named buffer pool.
FC MBS Oversubscription Factors and WRED Mega-Pool 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
buffer management purposes, each forwarding class is configured with an MBS oversubscription factor
(OSF) on the IOM using the osf command. The MBS oversubscription factor is used by the system as a pro-
Page 552 7750 SR Interface Configuration Guide