I am trying to determine an issue with our network across an mpls. 3 sites running qos on all of them. Pushing voip only. 2 sites on 3825's that do data and voice to 2 separate physical lan and wan segments. 3rd site 2951 doing voice only. Need to determine where the breakdown is that is degrading call quality. The isp says its not them. How do I go about determining the cause.