If jitter at the input port of a network element (NE) exceeds a threshold value, errors or loss of data will occur in the digital signal. As jitter is present in all telecommunications networks to some degree, NEs must be designed to tolerate a sufficient level of jitter to ensure they don’t lose lock or introduce errors when certain values of jitter are present. The ITU-T specifies the lower limit of maximum tolerable input jitter (MTIJ) in the form of an ITU-T jitter tolerance mask. All NEs must be rigorously tested against this minimum standard to ensure their mea- sured input jitter tolerance is greater than the ITU-T mask.