Delay and Jitter

Data traffic is usually short and comes in bursts. Data networks like the Internet are designed to manage these bursts of traffic from many sources on a first-come, first-served basis. Data packets are sent to multiple destinations, often without any attempt to keep them in a particular order.

Voice networks are designed for continuous transmission during a call. The traffic is not bursty, and the conversation uses a specific amount of bandwidth between the two ends during the call.

Several features of data networks are unsuitable for voice telephony:

• Data network design delivers data at the destination, but not necessarily within a certain time, producing delay (latency). In data networks, delay tends to be variable. For voice messages, variable delay results in jitter, an audible choppiness in conversations.
• Variable routing also can result in loss of timing synchronization, so packets are not received at the destination in the proper order.
• Data networks have a strong emphasis on error correction, resulting in repeated transmissions.

Data network concepts include prioritization of traffic types to provide some form of greater traffic reliability, for example, for interactive transactions. However, data requirements tend to not be as strict as most voice requirements.

The 4600 Series IP Telephones include a dynamic jitter buffer. This feature automatically smooths jitter to improve audio quality.