Shared-Queue QoS Policies
Quality of Service Guide 665
Default 10%
Parameters percent — The amount of queue buffer space, expressed as a decimal percentage of the MBS.
Values 0 to 100 | default
mbs
Syntax mbs percent
no mbs
Context config>qos>shared-queue>queue
Description This command specifies the relative amount of the buffer pool space for the maximum buffers for a
specific ingress network XMA or MDA forwarding class queue or egress network port forwarding
class queue.
The MBS value is used to by a queue to determine whether it has exhausted its total allowed buffers
while enqueuing packets. Once the queue has exceeded its maximum amount of buffers, all packets
are discarded until the queue transmits a packet. A queue that has not exceeded its MBS size is not
guaranteed that a buffer will be available when needed or that the packet’s RED slope will not force
the discard of the packet. Setting proper CBS parameters and controlling CBS oversubscription is one
major safeguard to queue starvation (when a queue does not receive its fair share of buffers). Another
is properly setting the RED slope parameters for the needs of the network queues.
The MBS size can sometimes be smaller than the CBS. This will result in a portion of the CBS for the
queue to be unused and should be avoided.
Default The mbs forwarding class defaults are listed in Table 45.
Table 45: MBS Forwarding Class Default Values
Forwarding Class Fowarding Class Label Default MBS
Network-Control nc 25
High-1 h1 25
Expedited ef 50
High-2 h2 50
Low-1 l1 25
Assured af 50
Low-2 l2 50
Best-Effort be 50
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