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New Member

Tweaking QoS port parameters and policing


Is there a mathematical method of configuring bandwidth weights and queue limits or is it more art than science? For example, using the 3550 series switches, when you perform auto-qos, it chooses the following parameters:

wrr-queue bandwidth 10 20 70 1

wrr-queue queue-limit 50 25 15 10

I need to know the reason for how this values were chosen, in order to understand how changing these values affect the overall queueing process. Is there some kind of best practice (recommended) values for setting them? I notice a pattern that bandwidth weights with the exception of the priority queue (qid 4) are larger; whereas the queue-limit values are lower for higher priority traffic, i.e. they get the smallest slice of the egress buffers.

Also the burst-byte value parameter in policing under policy map. How do you obtain an appropriate value for this? How does that relate to the access-rate?

In the auto-qos it gives the same 8000 byte value to the burst byte, see below:

policy-map AutoQoS-Police-SoftPhone

class AutoQoS-VoIP-RTP-Trust

set dscp ef

police 320000 8000 exceed-action policed-dscp-transmit

class AutoQoS-VoIP-Control-Trust

set dscp cs3

police 32000 8000 exceed-action policed-dscp-transmit

Any help is greatly appreciated.

Many thanks


Re: Tweaking QoS port parameters and policing

To allocate bandwidth between standard transmit queue 1 (low priority) and standard transmit queue 2 (high priority), use the wrr-queue bandwidth command is used. Use the no form of this command to return to the default settings.

New Member

Re: Tweaking QoS port parameters and policing

Thanks for you time. However, the question was more to do with techniques or best practice or mathematical process, to come up with the appropriate values for wrr weights and allocating the buffer using the queue-limit. I have read a lot of documentation, but they never really dig deeper.

Also reference you gave is for the 6500 and not the 35550, they are different.

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