QoS for Voice

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Dec 11th, 2007
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I am having a cisco voice infrastructure with 4506 switch to which ip phones are connected.Desktops are connected to LAN through ip phones.I have configured voice vlans and access vlans on the sitch ports.

All ip phones are in same LAN and hence no voice calls will go through wan.

Also the voice traffic is limited to 5MB and for this policy map is configured.

Do I have to configure additional QoS for the voice traffic in this scenario ?



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allan.thomas Tue, 12/11/2007 - 02:38
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Typically the recommendation is that you should enable QoS policies, classification and marking policies to establish and enforce trust boundaries as well as policers to protect against undesired flows at the access edge of the LAN.

In most cases the access edge links can be underutilised, generally the LAN is provisioned to accommodate oversubscription between access, distribution and core layers.

However in your scenario or network deployment model the typical QoS model is not really applicable.

Therefore I would not expect oversubscription, I would recommend where applicable that you configure your egress or transmit queues as appropriate and also trust your IP Phones, Voice-Gateway, CCM Devices etc thus everthing else if treated as best effort.



mheusing Tue, 12/11/2007 - 02:45
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A good resource for QoS related questions is the "Enterprise QoS Solution Reference Network Design Guide Version 3.3", which can be found at


It contains a section on Campus QoS and gives best practice examples also for the Catalyst 4500 for various scenarios.

In general I would enable QoS on all trunk ports and phone ports with priority queueueing to ensure QoS for voip. For that matter, auto qos for voip will most likely be sufficient in your case.

Regards, Martin


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