Alcatel-Lucent 7950 Quality Of Service Manual page 282

Service Queue QoS Policy Commands
mbs
Syntax mbs {[0..2625][kilobytes] | [0..2688000]bytes | default }
no mbs
Context config>qos>sap-ingress>queue
config>qos>sap-egress>queue
Description The Maximum Burst Size (MBS) command provides the explicit definition of the maximum amount of
buffers allowed for a specific queue. The value is given in kilobytes and overrides the default value for the
context.
The MBS value is used by a queue to determine whether it has exhausted all of its buffers while enqueuing
packets. Once the queue has exceeded the amount of buffers allowed by MBS, all packets are discarded until
packets have been drained from the queue.
The sap-ingress context for mbs provides a mechanism for overriding the default maximum size for the
queue.
The sum of the MBS for all queues on an ingress access port can oversubscribe the total amount of buffering
available. When congestion occurs and buffers become scarce, access to buffers is controlled by the RED
slope a packet is associated with. A queue that has not exceeded its MBS size is not guaranteed that a buffer
will be available when needed or that the packets 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 services on this port.
If the CBS value is larger than the MBS value, an error will occur, preventing the MBS change.
The no form of this command
Default
default
Parameters
[0..2625][kilobytes] — The size parameter is an integer expression of the maximum number of kilobytes
of buffering allowed for the queue. For a value of 100 kbps enter the value 100 and specify the
kilobytes parameter. A value of 0 causes the queue to discard all packets.
Values
[0..2688000]bytes — The size parameter is an integer expression of the maximum number of bytes or
kilobytes of buffering allowed for the queue. For a value of 100 kbps enter the value 100 and specify the
kilobytes parameter. A value of 0 causes the queue to discard all packets.
Values
packet-byte-offset
Syntax packet-byte-offset {add bytes | subtract bytes}
no packet-byte-offset
Context config>qos>sap-ingress>queue
Description
This command is used to modify the size of each packet handled by the queue by adding or subtracting a
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returns
the MBS size assigned to the queue to the value.
0..2625
0..2688000
7950 XRS Quality of Service Guide