/mcpHow this relates to jitter is if this occurs, and some packets need to be buffered in the frame network, they have a longer latency in getting to the remote router. However, when there is no congestion, they get through in the latency time that you normally expect. This causes a variation in the delta time between packets received at the remote router. Hence, jitter. Fragmentation Fragmentation associates more with serialization delay than with jitter. However, under certain conditions, it can be the cause of jitter. Fragmentation should always be configured in the Frame Relay map class when doing packetized voice. The configuration of this parameter has two effects on the interface. The first effect is that all packets larger than the size specified are fragmented. The second effect is less apparent, but is just as important. If you look at the interface on which fragmentation is configured, you can see the effect of this command. Without fragmentation, the queuing strategy shown in the output of the show interface x command shows that first in first out (FIFO) queueing is in use. Once fragmentation is applied to the Frame Relay map class, the output of this command shows the queueing strategy as dual−FIFO. This creates the priority queue that is used for voice traffic on the interface. It is strongly suggested that the fragmentation value be set to the values that are advised in the Fragmentation section of the VoIP over Frame Relay with QoS document. If you still experience jitter problems at the recommended value, lower the fragmentation value one step at a time until voice quality becomes acceptable. Queueing There are two generally accepted queueing methods used for VoIP traffic in this type of environment: IP RTP Priority Queueing • Low Latency Queueing • One method or the other should be used, they should not both be configured. If the queueing operation looks correct according to the documentation, then you can conclude that queueing works properly and the problem lies elsewhere. Queuing is generally not a cause of jitter since the variations in delay created by it are relatively small. However, if VoIP packets do not get queued properly and there is data on the same circuit, jitter can result. Conclusion Jitter is a variation in packet latency for voice packets. The DSPs inside the router can make up for some jitter, but can be overcome by excessive jitter. This results in poor voice quality. The cause of jitter is that a packet gets queued or delayed somewhere in the circuit, where there was no delay or queueing for other packets. This causes a variation in latency. Jitter can be caused both by router misconfiguration and by PVC misconfiguration by the carrier or provider. Related Information Voice Technology Support • Voice and Unified Communications Product Support • Troubleshooting Cisco IP Telephony • Technical Support − Cisco Systems • Contacts & Feedback | Help | Site Map © 2014 − 2015 Cisco Systems, Inc. All rights reserved. Terms & Conditions | Privacy Statement | Cookie Policy | Trademarks of Cisco Systems, Inc.