Alcatel-Lucent 7950 Quality Of Service Manual page 378

Queue Group Commands
high-prio-only
Syntax high-prio-only percent
no high-prio-only
Context config>qos>qgrps>egr>qgrp>queue
config>qos>qgrpid>ing>qgrp>queue
config>qos>qgrpid>ing>qgrp>policer
Description
The high-prio-only command configures the percentage of buffer space for the queue, used exclusively by
high priority packets. The specified value overrides the default value for the context.
The priority of a packet can only be set in the SAP ingress QoS policy and is only applicable on the ingress
queues for a SAP. The high-prio-only parameter is used to override the default value derived from the net-
work-queue command.
The no form of this command restores the default high priority reserved size.
Parameters percent — The percentage reserved for high priority traffic on the queue. If a value of 10KBytes is desired,
enter the value 10.
Values
mbs
Syntax mbs size [bytes | kilobytes]
no mbs
Context config>qos>qgrps>egr>qgrp>queue
config>qos>qgrpid>ing>qgrp>queue
config>qos>qgrpid>egr>qgrp>policer
config>qos>qgrpid>ing>qgrp>policer
Description For queues, the Maximum Burst Size (MBS) command the default maximum buffer size for the template
queue. The value is given in kilobytes.
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 port Ethernet access ingress and egress queue group context for mbs provides a mechanism for overrid-
ing 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 over-subscription 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 parame-
ters 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.
Page 378
0 — 100, default
7950 XRS Quality of Service Guide