nt? There are two basic mechanisms available to distribute information on leap seconds: Use a source of Coordinated Universal Time (UTC) that also distributes leap second information Via configuration and operational procedures based on information made available by the In- ternational Earth Rotation and Reference Systems (IERS) service and its Bulletin C GNSS systems carry leap second information in their timing and navigation messages to enable re- ceivers to learn about and cope with leap second events. The GNSS systems signal that a leap second event is approaching and what sort of event it might be (the most common being the 61- second minute). This information allows the GNSS receiver to accurately translate the timescale native to the GNSS system into an accurate value for UTC. See Chapter 3 for more details on how the GNSS systems and their timescales work. If the receiver supports the capability, and the ToD message format allows it, then the GNSS re- ceiver may be able to pass that information to the PTP master function using the ToD link. That way, the PTP master can learn about the change and then use the Announce message to signal the downstream slaves that the leap event is coming. The second approach is to use configuration on the PTP GM clocks to signal the leap events whenever the IERS announces an upcoming future event. Normally, bulletin C provides a warning of about five months before the event, allowing sufficient time to prepare for the impending change. The configuration on the GM indicates what the new (changed) time offset between TAI and UTC will be and the date and time from when it takes effect. So, a configuration might indicate that the leap second offset will change (from the current 37 seconds) to 38 seconds on 31-Dec-2021 at the second following 23:59:59 UTC. Whatever method is used, the GM clocks will use that information to fill in the Announce message with the new leap second information when needed. Twelve hours before the event occurs, the PTP GM changes the advertised Announ