 from a router, the MTIE data needs to be compared to the SyncE mask from G.8262 and not from some other standard like G.812 (which covers SSU/BITS clocks). Figure 5-20 represents the various types of categories of noise performance and the point at which they are relevant (and could be measured). Clock inputs (Clock-1) (Clock-2) (Clock-3) Noise Noise Noise generation transfer tolerance Figure 5-20 Noise Generation, Transfer, and Tolerance The sections that follow cover each of these categories in more detail. Noise Generation Figure 5-21 illustrates the noise generation at the output of Network Element-1 (NE-1) and hence the measurement point for noise generation. Noise generation is the amount of jitter and wander that is added to a perfect reference signal at the output of the clock. Therefore, it is clearly a per- formance characteristic of the quality or fidelity with which a clock can receive and transmit a time signal. Figure 5-21 depicts some amount of noise that gets added and is observed at output, when an ideal (perfect) reference signal is fed to the clock. Freq + Freq + phase phase Noise generation Figure 5-21 Noise Generation One analogy that might help is that of a photocopier. If you take a document and run it though a photocopier, it will generate a good (or even excellent) copy of the document. The loss of quality in that process is an analogy for noise generation. But now, take a photocopy of that copy of the docu- ment, and a photocopy of that copy. Repeat that process, and after four to five generations of copies, the quality will have degraded substantially. The lower the noise generated in each cycle of the copy process, the more generations of copies can be made with acceptable quality. For transport of time across a network, lower noise generation in each clock translates into a better clock signal at the end of the chain, or the ability to have longer chains. That is why noise genera- tion is a very important characteristic for clocks. Noise Tolerance A slave clock can lock to the input 