restricted range of values. Like its parent, this profile sets numer- ous PTP parameters to specific values, such as the message interval for Announce, Sync, and Pdelay_Req is 1 per second. With singly attached clocks, this is a somewhat restricted subset of the 1588-2008 default profile with the use of the default BMCA. When clocks incorporate the optional double attachment, then the profile makes use of the extended BMCA as specified in IEC 62439-3:2016, Annex A. These PIP and PUP profiles make substantial use of TCs and have stricter requirements on TC per- formance than that of boundary clocks. In these power topologies, a boundary clock is a clock that has ports in two or more domains. The boundary clock synchronizes to a grandmaster in one do- main and acts as a grandmaster in another domain. The BC is used to time-synchronize two or more separate networks infrastructures to one grandmas- ter without the need of bridging data packets between the networks. One way to think of it is that they act somewhat like a router connecting two LAN broadcast domains together. The IEC/IEEE published PUP in 2016 and it has a stability date of 2020, which means that a new version is expected in 2021. As this profile is a copy of the IEC 62439-3 PIP profile, the preparatory work has been undertaken by that group in the IEC, and it is reflected in a new version of 61850-9-3 (edition 2). Among the updates is that it aligns with the new PTPv2.1 version of IEEE 1588-2019. Devices implementing the PUP profile tend to be equipment specialized for substation and power grid monitoring like intelligent electronic devices (IED) and phasor measurement units (PMU). On the other hand, the profile is not SO widely implemented in general-purpose routers deployed by ser- vice providers. Every 2 years, the industry gets together to perform IEC 61850 interoperability (IOP) testing activ- ities, with (as of writing) the last taking place in October 2019. Part of that testing is to test the per- formance and capability of PTP implementations o