2 specification for a PTP boundary and slave clock defines the required holdover performance in absence of PTP pack- ets for both cases-constant temperature and variable temperature. 5.4 Transient Response Holdover is the state that a clock transitions to whenever the input reference clock is lost. It has been shown that providing good, long-duration holdover to a failure of the reference signal is neither easy nor inexpensive. However, there could be multiple reference clocks simultaneously available to a slave clock, offering the ability to provide backup signals in the case of failure. Con- sequently, network designers prefer a design where multiple references are available to the network elements-providing redundancy and backup for timing synchronization. The question arises, how should the clock behave when an input reference clock is lost and the clock decides to select the second-best clock source as the input reference? The behavior during this event is characterized as the transient response of a clock. Multiple reference inputs to a clock could be traceable (via different paths) to the same source of time (such as a PRTC) or back to different sources. The clock quality information (such as Ethernet synchronization messaging channel (ESMC) and PTP packets) sent through the network shows the quality of the source of time that these separate references offer. The software managing the slave clocks then decides which backup reference clock to use based on the quality information. As ex- pected, a high-quality reference is preferred over a lower-quality reference clock. For cases where there are multiple inputs, the network designer might assign the input references a priority, SO that the slave clock can decide in what order the input is preferred. So, when the highest priority (say priority 1) reference clock fails, the slave must decide whether there is another refer- ence available to provide an input signal. The slave selects one of the remaining sources available out of those signaling the highest qual