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Wander accumulates in the network and may result in buffer underflows/overflows and/or the ability to lock to the incoming timing reference. High level of wander may also result in excessive time error in the nodes for the case of time sync applications.
Excessive level levels of jitter can create bit errors (and related packet drops), or reduce the margin to other sources of errors.
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As long as these remain isolated spikes, e.g. impacting at most 1 bit over 2.5 hours (i.e. corresponding to 10-13 at 1 Gbps), these may be ignored and can be considered outside the scope and the intention with of the jitter measurement. In fact, 1 bit in 2.5 hours would meet the typical performance objectives with good margin.