Alcatel-Lucent 7450 Quality Of Service Manual page 357

mbs
Syntax mbs size [bytes | kilobytes]
no mbs
Context config>qos>sap-egress>queue
config>qos>sap-ingress>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 bytes or 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 or channel.
The no form of this command returns the MBS size assigned to the queue to the value.
Default default
Parameters size [bytes | kilobytes] — The size parameter is an integer expression of the maximum number of
packet-byte-offset
Syntax packet-byte-offset {add bytes | subtract bytes}
no packet-byte-offset
Context config>qos>sap-egress>queue
Quality of Service Guide
bytes or kilobytes of buffering allowed for the queue. The default unit is kilobytes; to
configure the MBS in bytes specify the bytes parameter. A value of 0 causes the queue to
discard all packets. The queue MBS maximum value used is constrained by the pool size in
which the queue exists and by the shared pool space in the corresponding megapool.
Values 0 to 131072 or default
Minimum configurable non-zero value: 1 byte
Minimum default value: maximum of 10ms of PIR or 64Kbytes
Service Egress and Ingress QoS Policies
357