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QOS Questions -

Hi All,

I have hitting my head hard to understand on how the Policing Works and what/how the Burst rate is calculated. Below is my Understand.

1. police 884000 8000 conform-action set-dscp-transmit ef exceed-action drop

Based on the above configured Police Command, the Mean Rate is 884kbps and the TOken Bucket Size is 8000 Bytes. Based on the Caculation 8000*8/884000 will dervice to 0.72 sec which is 72ms. So it means we can transfer 8000 bytes in 72ms. Can you help me to understand what this really means, does this mean that every 72ms i will get a new Bucket? Because with this current policy we are seeing packet drops even when the link utilization is not high.

Based on few Calculations from our support forums, it seems the burst should be 10% of the mean rate. Which means 800ms to transfer 88400 bytes. What does this mean and how does this prevent the packet drops we are seeing.

2. The next is the understanding on the exponential-weighted-constant values. There are values we can set from 1 to 16. Which means when we set 1(too low), the Average Queue Size tracks the current queue very closely and it will overreact even for small overburst. Which means the more the constant value the slow the Average Queue size is calculated based on the current queue size?

3. Also in the random detect dscp we set the dscp(10) min threshold(32) max threshold(51) and drop probability(10). How do we know what is the max Output Queue for the interface? Is it the 0/1000/64/0 ? is the 1000 the maximum output queue for the interface and is this the figure we are playing around in the min/max threshold? Also when it says 1000 what is the size of one queue out of the 1000, means what is the packet size can the one queue take? Does the packet size matter for the queue?

4. Also is there a way in the QOS where we can reserve the Bandwidth for the Particular Class? means if it set priority 884 for a Voice Class, it means it does not reserver the 884 for me at all times but other classes can the 884 bandwidth if it is free.

Hope anyone can help me to better understand it.



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