IP networks are “jittery” in their nature.
When packets are sent, it is not guaranteed that they will be delivered in the same time gaps.
Since voice and video are time-sensitive, when media packets are received, they need to be collected, reordered and then timed based on the sequence and differences in which they were generated and not the sequence and timing in which they were received. This is handled by the Jitter Buffer in the Media Engine.