Above Cir Discard With Pir Bypass - Alcatel-Lucent 7450 Quality Of Service Manual

HSMDA QoS Model
Since the HSMDA only updates a single counter set per packet, overriding the counter for a
packet causes that packet not to be represented within the default counter-id for the queue. If
the queue counter-id is being used to determine CIR or PIR accuracy or basic throughput for
a queue, any packets forwarded through the queue using a counter override is considered.

Above CIR Discard with PIR Bypass

HSMDA Ingress Queue Policing Mode
Since HSMDA queue-based CIR and PIR leaky bucket behavior is driven by scheduling
events from the queue, a true policing function where the ingress offered rate determines the
color of the packet (green, yellow or red) is not available, by default. While enabling a PIR-
based shaping rate for the queue will perform a similar function, the shaping function is
simply stopping the queue from scheduling. When the queue is stopped, packets are allowed
to be buffered within the queue up to the RED slope or MBS-configured limits. The jitter for
a shaping queue is based on how full the queue can get and how fast the queue is scheduled
(influenced by the queue PIR, queue group PIR and ingress secondary shapers). While the
MBS for the queue may be configured to minimize jitter by preventing an excessive amount
of data to accumulate in the queue, a policing mode can be enabled on the queue that uses the
CIR leaky bucket to dynamically discard packet above the CIR threshold.
The HSMDA ingress queue policing mode behaves normally while the CIR leaky bucket is
below its configured threshold. If the CIR fill depth rises above the threshold, the packet is
discarded without updating any of the ingress schedulers PIR leaky buckets. The result is that
while the queue is operating within its CIR, scheduled packets will be forwarded to the
ingress forwarding plane for further processing and each packet will update all applicable
PIRs. But when the queue scheduled rate rises above the CIR, scheduled packets are
discarded. By discarding out-of-profile packets, the policing rate is enforced without
unnecessary jitter based on queue congestion.
In order for ingress policing mode to function properly, the following configuration
guidelines should be observed:
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• The queue should be scheduled at the highest appropriate strict scheduling priority.
If the queue is not scheduled at a high enough priority, scheduling from the queue
may momentarily stall. The scope of this issue is limited since the ingress port
bandwidth is less than the available scheduling bandwidth to the ingress forwarding
plane.
Quality of Service Guide