Interface Congestion Definition and interaction with WFQ

Hi Team:

Have a question regarding QoS. I know that the built in policer for CBWFQ
LLQ takes effect only during congestion.

I also know that the "bandwidth" command only guarantees traffic during
congestion.

For example, if you have a GigE NNI interface to a carrier who provides a
10Mb ethernet service, and you have QoS configured as follows.

int Gi0/1
bandwidth 10000
ip add x.x.x.x
service-policy output TEST

policy-map HQoSTEST
class class-default
shape average 10000000
service-policy TEST

policy-map TEST
class EF
priority percent 10
  police 1000000
  conform transmit
  exceed set-dscp-default transmit
class AF31
  bandwidth percent 30
class class-default
bandwidth percent 30
random-detect dscp-based

My question is how does the router determine that "congestion" has occurred.
 Does it look strictly at the interface buffers - does the full Gig have to
be being sent before CWFQ is notified of congestion?

Is the HQoS really necessary, or does it just go off of the bandwidth
CONFIGURED on the interface.

I would think that before traffic is passed to the WFQ scheduler, it has to
pass through the shaper. Does the shaper just blindly take the first 10Mbps
that comes to it - regardless of priority - and pass to WFQ. In this case,
if the shaper fills up with 10Mbps of BE traffic, and then an EF packet
comes along, will it be buffered before it is passed to WFQ scheduler?

So is it preferred NEVER to use a hierarchical shaper - when we can avoid
it?

Thanks,

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Received on Wed Mar 17 2010 - 11:20:33 ART