release jitter of tasks

there is a distinction between the real activation request and the actual activation instant of a task.

release jitter of packets

The maximum difference in the latency between two packets within a flow.

Low jitter is often a requirement for video streams or other real time data for which the regularity of data arrival is important.

The jitter times gives a lower bound on the size of buffer required.

For example, in a video playback system, the size of the buffer required to hold packets before playback is determined by the jitter, not the average latency.

release jitter J_i  denotes the maximum deviation of successive packets released from its period.

If a packet from f_i is generated at time a (real activation), then it will be released for transmission by time a+J_i (actual activation) 

and have global deadline a + D_i, and local deadline a+J_i + D_i.