In network communications, when the latency between the sender and the receiver's equipment fluctuates, we have what is called jitters. The de-jitter is a buffer used by the receiving end to reduce the jitter and sequence the processing of incoming packets in regular intervals. This article is a basic introduction to de-jitters, how are they used with VoIP, and considerations for choosing an adequate de-jittering buffer size.
How a de-jittering buffer works
A jitter is generally defined as the variation in network latency. The receiving end uses dejittering buffer to reduce the jitter. Jitter buffers (also known as playout buffers) are used to change asynchronous packet arrivals into a synchronous stream by turning variable network delays into constant delays at the destination end systems [ Quality of Service Design Overview (Cisco Systems) ]. In VoIP applications, when voice frames are played back in the receiver's system, the decoder must be fed with frames on time. If the decoder does not receive the needed frame on time, the receiver will experience a moment of silence. In order to avoid this, frames are buffered for a certain delay before being fed to the decoder. If a packet takes more than the average time to travel the network, the decoder will keep using frames from the de-jttering buffer until the late packet arrive. If the decoder finishes up all the buffered frames, the original problem occurs; the user will experience moments of silence. When late packets arrive they are discarded and the palyback resumes only after a frame arrives before its schedules playback time.
Ref . from : http://www.codealias.info/technotes/de-jittering_buffers_and_realm_time_network_services
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