 are three main timing flows: PTP input to the PTP and 1PPS outputs: Depicted by solid lines in Figure 9-28. Frequency input to the PTP and 1PPS outputs: Depicted by dashed lines in Figure 9-28. This path can transfer phase wander from the physical layer frequency interface to the PTP and 1PPS output interfaces. Frequency input to frequency output: Depicted by the line from left to right at the bottom of Figure 9-28. Each of these flows illustrated in Figure 9-28 also has a bandwidth associated with it, which de- scribes the characteristics of the filter in the path of the input signal through the clock. T-BC/T-TSC PTP to PTP Time & Frequency to PTP phase master slave recovery PTP to 1PPS Frequency to 1PPS Local oscillator Frequency Frequency recovery Frequency to frequency Figure 9-28 Noise Transfer Paths Through a T-BC/T-TSC The frequency clock uses a phase-locked loop (PLL) (generally a hardware component) for fre- quency recovery. This PLL employs an LPF to filter the high-frequency noise from the input signal (remember that bandwidth also differentiates between jitter and wander). According to G.8262 this bandwidth is in the range of 1 Hz to 10 Hz for a (SyncE) Ethernet equipment clock (EEC). In a similar way, the time clock also uses a PLL (albeit software based) to recover phase and time from the input signals. For a T-BC/T-TSC with full timing support, the inputs to this PLL are the PTP messages and frequency recovered from frequency clock. The concepts behind the use of PLLs in building time clocks is explained in detail in Chapter 12. The time clock also uses an LPF to filter out jitter in the noise on the input from the PTP packets. However, according to G.8273.2, the bandwidth for this LPF must be between 0.05 Hz and 0.01 Hz, which is different to the bandwidth used by the frequency clock. For the path from frequency to PTP (and 1PPS), the two filters described earlier combine their ef- fect: the frequency input is first filtered by frequency clock and then gets filtered by the time clock but using a 