ter PEC-S-F packet-based equipment clock-slave-frequency PEC-S packet-based equipment clock-slave packet-based equipment clock PTP hardware clock PHYsical Layer (of OSI Reference Model)-an electronic device PTP Industry Profile pktSelected2wayTE packet-selected two-way time error phase-locked loop Physical Medium Attachment phasor measurement unit Precise Networked Clock Synchronization packet network timing positioning, navigation, and timing proof of concept passive optical networking (optical broadband) point of presence POSIX Portable Operating System Interface parts per billion parts per million primary reference clock (SDH) pseudorandom noise Parallel Redundancy Protocol primary reference source (SONET) PRTC-A primary reference time clock-class A PRTC-B primary reference time clock-class B primary reference time clock packet switched primary synchronization signal public switched telephone network packet transport network precision time protocol PTPoE PTP over Ethernet PTPoIP PTP over Internet protocol PTPv1 precision time protocol according to 1588-2002 PTPv2.1 precision time protocol according to 1588-2019 PTPv2 precision time protocol according to 1588-2008 partial timing support packet timing signal fail Power Utility Automation Profile Q13 or Q13/15 Question 13 of Study Group 15 of the ITU-T (concerned with sync) quality level quality of experience quality of service quadrature phase-shift keying QSFP+ quad small form-factor pluggable-plus (transceiver) quasi-zenith orbit Quasi-Zenith Satellite System R15/Rell5 Release 15 (of the 3GPP standards) R16/Rell6 Release 16 (of the 3GPP standards) R17/Rell7 Release 17 (of the 3GPP standards) RADIUS Remote Authentication Dial In User Service radio access network rubidium Radio Equipment (CPRI) Radio Equipment Control (CPRI) radio frequency/function Request for Comments (IETF document) request for information request for proposal Radio Intelligent Controller RJ-45, RJ-48c registered jack 45, 48c RJ-45 registered jack 45 root mean square radio over Ethernet Remot