ocks, which can be thought of PTP repeaters. These have two or more ports and receive time on one port and retransmit it on the other ports. In general, a boundary clock is a specialized Ethernet switch or router, SO each PTP port corresponds to a data port and the device also forwards non-PTP data traffic between ports. In the FTS and PTS profiles, these three types of nodes are referred to as: T-GM-Telecom grandmaster T-BC or T-BC-P-Telecom boundary clock or telecom boundary clock-partial, depending on if it is used for FTS or PTS T-TSC or T-TSC-A-Telecom time slave clock, again depending on the profile There are a number of different messages used by PTP, which depending on the profile are sent either as raw Ethernet frames, with their own EtherType value, or as the payload of UPD/IPv4 or UDP IPv6 datagrams, and all of which have a common header format followed by message-specific information. These messages can be divided into two basic types: Event messages-These are the messages that are actually used to transport time across the network and therefore are considered time-sensitive. These messages are timestamped at each end, meaning that the sender captures the exact time the message is sent using its clock and the receiver does the same with its local clock. General messages-Messages that are used by PTP but those are not time-sensitive, so do not get timestamped. The first step in PTP synchronization is to decide which node is going to be master in the network. It might seem obvious that this will be the one with a GNSS receiver attached to it. However, as mentioned earlier, it is possible that there might be multiple such candidates to provide a degree of redundancy. Although any one of these could do the job of Grandmaster for the network, only one can in general have that role at once. To decide which one, each candidate for the role broadcasts a general message, called an Announce message, that out- lines the quality of the clock the node can offer. Every slave in the network receives all of these Ann