time, the slave then chooses its master. PIP Profiles and Annexes IEC 62439-3 Annex A specifies how to attach clocks to duplicated networks paths and how to support simultaneously active redundant master clocks for all profiles. IEC 62439-3 Annex B specifies the L2PTP profile for substation automation IEC/IEEE 61850-9-3. In contrast to IEC/IEEE 61850, double attachment by PRP or HSR is mandatory. IEC 62439-3 Annex C specifies two profiles, L3E2E and L2P2P, that are subsets of IEEE Std 1588 Precision Time Protocol (PTP) when clocks are singly attached. IEC 62439-3 Annex D is a tutorial for IEEE 1588 that concentrates only on PIP. IEC 62439-3 Annex E contains the SNMP objects for managing the doubly-attached clocks. Main features IEC 62439-3 Annex C uses the following IEEE Std 1588 options: uses the PTP timescale based on TAI International Atomic Time, also delivers UTC Coordinated Universal Time transmits the clock correction indifferently with 1-step (preferred) or 2-step (can be mixed) operates with the default best master clock algorithm, performed by master and by slave clocks supports both options to measure the link delay: L3E2E: End-to-end measurement (Delay_Req/Delay_Resp) over Layer 3 (Internet Protocol) to fulfill the requirements of ODVA; L2P2P: Peer-to-peer measurement (Pdelay_Req/Pdelay_Resp) over Layer 2 Ethernet (IEEE 802.3) links. Performance IEC 62439-3 Annex C aims at an accuracy of better than 1 μs after crossing 15 bridges with transparent clocks. It assumes that all network elements (bridges, routers, media converters, links) support PTP with a given performance: Grandmaster (GC): 250 ns maximum inaccuracy Transparent Clocks (TC): 50 ns maximum inaccuracy Boundary Clocks (BC): 200 ns maximum inaccuracy Media Converters: 50 ns maximum jitter and 25 ns maximum asymmetry Link asymmetry: 25 ns maximum asymmetry By relying on these guaranteed values, the network engineer can calculate the time inaccuracy at different nodes of the network and place the clocks, especially the grandmaster clocks suitably. IEC TR 61850-90-4 (Network engineering guidelines) gives advice on the use of IEC/IEEE 61850-9-3 in substation automation networks. IEEE 1588 settings IEC 62439-3 Annex C restricts the parameters of IEEE Std 1588 to the following values: domainNumber: 0 (default range) Announce interval: (default range) 1 s (L2P2P) or 2 s (L3E2E) Sync interval: 1 s (fixed) Pdelay interval: 1 s (fixed) Announce receipt time-out (number of Announce interval that has to pass without receipt of an Announce message before Announce timeout is issued): 3 (fixed) priority1: 255 for slave-only