child jitter vs parent shaping vs child class-default on 871 and 1841

Hi, I was wondering in anyone has came across the same problem: Implementing parent policy map with shaping on class-default on Cisco

871 or 1841 will cause higher jitter on child traffic class even if it is LLQ. I guess it should be the same behavior on other Cisco access platforms. Example:

policy-map Child class voip priority 500 police 500000 class data bandwidth 400

policy-map Parent class class-default shape average 2000000 service-policy Child

Interface FastEthernet 4 service-policy output Parent

After trying different burst size parameters on parent shaping I found out that jitter can be minimized by reducing parent shaping burst size. By minimizing this parameter child policy-map reduced default allocated bandwidth to class-default - 15% or even less. Which is not what Cisco tells - 75% + 25%. I know that Cisco does not recommends to tune shaping burst size, but I could not find any other way to reduce jitter. IOS Version:


Regards, Robertas

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