Service Egress and Ingress QoS Policies
Quality of Service Guide 355
bytes — The bytes qualifier is used to specify that the value given for size must be interpreted as
the burst limit in bytes. The byte qualifier is optional and mutually exclusive with the
kilobytes qualifier.
kilobytes — The kilobytes qualifier is used to specify that the value given for size must be
interpreted as the burst limit in Kilobytes. The kilobyte qualifier is optional and mutually
exclusive with the bytes qualifier. If neither bytes nor kilobytes is specified, the default
qualifier is kilobytes.
cbs
Syntax cbs size-in-kbytes
no cbs
Context config>qos>sap-egress>queue
config>qos>sap-ingress>queue
Description This command provides a mechanism to override the default reserved buffers for the queue. It is
permissible, and possibly desirable, to oversubscribe the total CBS reserved buffers for a given access
port egress buffer pool. Oversubscription may be desirable due to the potentially large number of
service queues and the economy of statistical multiplexing the individual queue’s CBS settings into
the defined reserved total.
When oversubscribing the reserved total, it is possible for a queue depth to be lower than its CBS
setting and still not receive a buffer from the buffer pool for an ingress frame. As more queues are using
their CBS buffers and the total in use exceeds the defined reserved total, essentially the buffers are
being removed from the shared portion of the pool without the shared in use average and total counts
being decremented. This can affect the operation of the high and low priority RED slopes on the pool,
causing them to miscalculate when to start randomly dropping packets.
If the CBS value is larger than the MBS value, the CBS is capped to the value of the MBS or the
minimum CBS value. If the MBS and CBS values are configured to be equal (or nearly equal) this will
result in the CBS being slightly higher than the value configured.
The no form of this command returns the CBS size to the default value.
Default default
Parameters size-in-kbytes — The size parameter is an integer expression of the number of kilobytes reserved
for the queue. If a value of 10KBytes is desired, enter the value 10. A value of 0 specifies that
no reserved buffers are required by the queue (a minimal reserved size can still be applied for
scheduling purposes) The CBS maximum value used is constrained by the pool size in which
the queue exists.
Values 0 to 104857 or default
Minimum configurable non-zero value: 6Kbytes on an FP2 and
7680 bytes on an FP3
Minimum non-zero default value: maximum of 10ms of CIR or
6Kbytes on an FP2 and 7680 bytes on an FP3
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