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

Discussion in 'Cisco' started by Robertas, Feb 23, 2007.

  1. Robertas

    Robertas Guest

    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:
    12.4(9)T1


    Regards,
    Robertas
     
    Robertas, Feb 23, 2007
    #1
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