Problem: Prioritization
Class based queuing routers apply different priority levels to different classes of traffic. Traffic classes may be determined by examining the TOS bits in IP headers or by analyzing the packet payload, the latter approach being more common in traffic shapers.
The TOS field in the IP header may be modified or ignored by routers and hence assigning a high priority to a packet does not guarantee that it will receive priority treatment.
Impact
High levels of jitter resulting from access link congestion cause excessive numbers of packets to be discarded, which leads to degraded voice quality.
Resolution
If you are using prioritization then examine packet traces from different segments of the network to see if the TOS field is being reset. Check the configuration of routers and also check with IP service providers to make sure that they do support prioritization of traffic.
Tools:
Conditions of use: The material on this site is copyright VoIP Troubleshooter LLC and may be freely used but not copied or downloaded. In making use of this site the user acknowledges that VoIP Troubleshooter LLC or Contributor has no liability for any issues or problems that may arise directly or indirectly as a result of such use. VoIP Troubleshooter LLC and Contributor are providing this material as-is with no warranty as to correctness or completeness and do not accept any responsibility for any issues or problems of any nature whatsoever that may arise from the use of the material on this site.