Jitter

Jitter
Jitter is what happens when packets arrive either earlier or later than expected, outside established
parameters for simple delay. The effect is to interfere with the smooth playback of certain
types of streaming traffic (voice, video, and so on), because the playback buffers are unable to
cope with the irregular arrival of successive packets. Jitter is caused by variations in delay, such
as the following:
Serialization delay
Serialization delay can cause jitter, with subsequent packets being of different
sizes. One technique that might be used to standardize this delay would be to make all
frames the same size, irrespective of their data content. This is the method used by Frame Relay
using the FRF.11 (for voice) recommendation, and by ATM. This solution is good for voice but
bad for data, because of the overhead created by increasing the number of frames per packet.
Serialization delay is simple to calculate using the formula bits in the packet or
the frame/data rate of the interface. Thus, a 1518-byte frame transmitted out of
a 10Mbits/second Ethernet interface takes 1.2 milliseconds. Just for the record,
I have also heard serialization delay referred to as insertion delay.
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Chapter 20 
Quality of Service (QoS)
Queue disposition
Queue disposition
can affect delay, because while packets at the front of
the queue may have constancy of delay, packets further back are behind an unknown number
of frames/packets at the front, giving rise to variability. Cisco provides a number of different
queuing options, allowing the most appropriate to be selected on a case-by-case basis.
Per-hop routing
Per-hop routing
behavior can affect delay variably, because subsequent packets
may travel to the same destination via different paths due to routing changes.