Alcatel-Lucent 7950 Quality Of Service Manual page 36

QoS Policies
class is traffic that has been marked as in-profile either on ingress classification or based on
interpretation of the QoS markings.
The HP-only for network queues are defined within network queue policies based on the
forwarding class. High-priority traffic for a specific traffic class is marked as in-profile either on
ingress classification or based on interpretation of the QoS markings.
Packet Markings
Typically, customer markings placed on packets are not treated as trusted from an in-profile or out-
of-profile perspective. This allows the use of the ingress buffering to absorb bursts over PIR from
a customer and only perform marking as packets are scheduled out of the queue (as opposed to
using a hard policing function that operates on the received rate from the customer). The resulting
profile (in or out) based on ingress scheduling into the switch fabric is used by network egress for
tunnel marking and egress congestion management.
The high/low priority feature allows a provider to offer a customer the ability to have some
packets treated with a higher priority when buffered to the ingress queue. If the queue is
configured with a hi-prio-only setting (setting the high priority MBS threshold higher than the
queue's low priority MBS threshold) a portion of the ingress queue's allowed buffers are reserved
for high priority traffic. An access ingress packet must hit an ingress QoS action in order for the
ingress forwarding plane to treat the packet as high priority (the default is low priority).
If the packet's ingress queue is above the low priority MBS, the packet will be discarded unless it
has been classified as high priority. The priority of the packet is not retained after the packet is
placed into the ingress queue. Once the packet is scheduled out of the ingress queue, the packet
will be considered in-profile or out-of-profile based on the dynamic rate of the queue relative to
the queue's CIR parameter.
If an ingress queue is not configured with a hi-prio-only parameter, the low priority and high
priority MBS thresholds will be the same. There will be no difference in high priority and low
priority packet handling. At access ingress, the priority of a packet has no affect on which packets
are scheduled first. Only the first buffering decision is affected. At ingress and egress, the current
dynamic rate of the queue relative to the queue's CIR does affect the scheduling priority between
queues going to the same destination (either the switch fabric tap or egress port). The strict
operating priority for queues are (from highest to lowest):
•
•
•
For access ingress, the CIR controls both dynamic scheduling priority and marking threshold. At
network ingress, the queue's CIR affects the scheduling priority but does not provide a profile
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Expedited queues within the CIR (conform)
Best Effort queues within the CIR (conform)
Expedited and Best Effort queues above the CIR (exceed)
7950 XRS Quality of Service Guide