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Unicast Master Port Selection in PTP: When should a slave port swipe right Five Minute Facts About Packet Timing In multicast PTP a slave port need only subscribe to the PTP multicast addresses and timing will come to it. However, in unicast PTP a slave port has to reach out to the master port it wants time from with PTP message requests. It is more of a client-server paradigm. This means that the slave port starts with the unicast addresses of the master port and sends the requests for Announce, Sync and Delay Response messages. Here I am talking about master and slave ports, not clocks, since they might refer to individual ports on a Boundary Clocks. The question we are looking today is: which master port? There are several approaches to answering this question: 1. The slave port could have the address of just one master port, and it uses that one. 2. The slave port could have a prioritized list of master ports. That way if the first one is unavailable or refuses to grant messages because of capacity management, then the slave port can try its luck with the next one on the list. 3. The slave port can compare the clock quality attributes of several master ports and pick the best one.