Alcatel-Lucent 7950 Quality Of Service Manual page 35

Committed Burst Size
The committed burst size (CBS) parameters specify the amount of buffers that can be drawn from
the reserved buffer portion of the queue's buffer pool. Once the reserved buffers for a given queue
have been used, the queue contends with other queues for additional buffer resources up to the
maximum burst size.
The CBS is provisioned on ingress and egress service queues within service ingress QoS policies
and service egress QoS policies, respectively. The CBS for a queue is specified in Kbytes.
The CBS for network queues are defined within network queue policies based on the forwarding
class. The CBS for the queues for the forwarding class are defined as a percentage of buffer space
for the pool.
Maximum Burst Size
The maximum burst size (MBS) parameter specifies the maximum queue depth to which a queue
can grow. This parameter ensures that a customer that is massively or continuously over-
subscribing the PIR of a queue will not consume all the available buffer resources. For high-
priority forwarding class service queues, the MBS can be relatively smaller than the other
forwarding class queues because the high-priority service packets are scheduled with priority over
other service forwarding classes.
The MBS is provisioned on ingress and egress service queues within service ingress QoS policies
and service egress QoS policies, respectively. The MBS for a queue is specified in Kbytes.
The MBS for network queues are defined within network queue policies based on the forwarding
class. The MBS for the queues for the forwarding class are defined as a percentage of buffer space
for the pool.
High-Priority Only Buffers
High priority (HP)-only buffers are defined on a queue and allow buffers to be reserved for traffic
classified as high priority. When the queue depth reaches a specified level, only high-priority
traffic can be enqueued. The HP-only reservation for a queue is defined as a percentage of the
MBS value.
On service ingress, the HP-only reservation for a queue is defined in the service ingress QoS
policy. High priority traffic is specified in the match criteria for the policy.
On service egress, the HP-only reservation for a queue is defined in the service egress QoS policy.
Service egress queues are specified by forwarding class. High-priority traffic for a given traffic
7950 XRS Quality of Service Guide
QoS Policies
Page 35