cE, filtering. The easiest way to understand this is to recognize that a PLL acts as a low-pass filter for its input signal and a high pass filter for its local oscillator. In other words, the output noise of the PLL, which is the value that needs to meet the limits in the various standards for robust performance, is a mix of the input noise and the local oscil- lator noise. The lower the PLL bandwidth, the more the local oscillator noise comes into play and vice versa. Now, a PLL used for a local function such as jitter cleaning may have a bandwidth of 100 kHz +, meaning that long-term stability of the local oscillator really is not an issue. However, for a SyncE PLL that has to filter network noise, the bandwidth is usually in the 1-10 Hz range, meaning that the long-term stability of the local oscillator comes into play. Typically, as already stated, a SyncE PLL will require a minimum of a TCXO to provide the necessary stability and could require an OCXO if support is needed for legacy networks that require a bandwidth as low as 100 mHz, though this is unlikely to be a factor in O-RAN. However, it is also necessary to consider the local oscillator stability needed for the PTP filtering, since that too has an "effective bandwidth," which is related to how aggressive the servo is at filtering out network PDV. This is normally considerably lower than the SyncE bandwidth-between 50 and 100 mHz for FTS and as low as 1 mHz or less for PTS. And this is where the value of SyncE comes into play. If PTP was used on its own, this would be the bandwidth that would have to be considered when selecting the local oscillator. In other words, an OCXO would likely be needed even for FTS. However, when SyncE is used in conjunction with PTP the physical-layer clock recovered from SyncE is itself a stable clock source that supplements the local oscillator. This means that the local clock source to the PTP DCO is coming from the filtered SyncE clock rather than directly from the local oscillator and, therefore, it might be possible