QOS for VOIP on ATM (878)

Unanswered Question
Feb 1st, 2010
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Will the following qos policy allow for full use of available bandwidth, if no congestion? (I dont believe it will?)

class-map match-any VOIP
match access-group name VOIP-IP
policy-map childpolicy
  class VOIP
  priority percent 40
  class class-default
  police rate 886000

interface ATM0.1 point-to-point


pvc CA 10/50

  ubr 1536

service-policy output childpolicy

As ATM does not support GTS( GTS : Not supported over ATM VCs) i.e. Cannot "shape" default traffic, is there any other way to allow default traffic to utilise all available bandwidth(Unless congestion of course) - In the above example, client has a 1.5Mb SHDSL service, and we want to give voip ip's 40% of the link if there is congestion(But allow default traffic to use the entire 1.5Mb if no voip traffic is present)

Also, Is it not best practise to apply qos policy to ingress traffic(As well as engress)

Thanks in advance.

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johnelliot6 Mon, 02/01/2010 - 21:39
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To add to the above - would removing the police rate, provide the behaviour we are after?

mlund Thu, 02/04/2010 - 07:49
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"class class-default
  police rate 886000"

This will allow traffic up to 886000bits/s and drop excess traffic, even if there are no congestions.

If You remove the policing entry, the default-class can use all available bandwidth.

I'm not 100% shure, but I believe that if you configure an vbr instead of an ubr you will be allowed to configure shaping.

As a general rule

Ingress policy is best suited for marking and policing

Egress policy is best for shaping and queuing.

But it is not mandatory to it that way.



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