ou do not just add them all together; the calculation depends on the type of noise. The cTE component from previous clocks in the chain passes through unchanged and any local cTE is simply added to it. The low-pass filtering of the clock removes the high-frequency dTE, SO the contribution to high-frequency dTE comes predominantly from the last network element in the tim- ing chain. Meanwhile, the low-frequency dTE accumulates somewhat haphazardly because it can- not be filtered. The high-band (or high-frequency) dTE is the jitter portion of the dTE. If all the network elements of the chain are adhering to standards for noise generation and transfer, this jitter portion is removed/filtered by each element in the path. And so, the high-band portion of the dTE is only con- tributed by the last network element. Low-band (or low-frequency) dTE is the wander portion of the dTE. As clocks use low-pass filters, any accumulated wander would easily propagate through the chain of nodes and hence this dTE gets accumulated for all the clocks of the chain. In summary: The cTE and any link asymmetry accumulates in a linear fashion (add it up). The high-frequency dTE (jitter) is mostly filtered from upstream and the main contribution comes from the last network element in the chain. The low-frequency dTE (wander) can arise haphazardly, but once it is present, it does accumu- late linearly in the chain. 9.6 Network Holdover If your application holdover performance relies on holdover, then you should also consult the sec- tion "Holdover" in Chapter 11 that is focused on the mobile use case. The section here, as in Chapter 11, starts by demonstrating how hard it is to maintain accurate holdover at reasonable cost. If holdover is important to you, then of course you need to consider it, but it comes attached with a considerable cost-holdover is not free. First, you should have a clear understanding of what good holdover (at a reasonable cost) looks like. Table 9-11 gives an idea of the performance of a PRTC that meets the performanc