IEEE 1588/PTP - Precision Time Glossary

Quick and Practical reference list of Acronyms used in Timing applications

1PPS           One Pulse Per Second time signal. Marks the beginning of standard second (TU-T G.703 and G.8271)

2Way TE     PTP Time Transfer Error (packet-based)

APTS          (GNSS) Assisted Partial Timing Support (ITU-T G.8275.2)

BDS            BeiDou (Big Dipper) Navigation Satellite System, Chinese GNSS

BC              Boundary Clock

BMCA         Best Master Clock (selection) Algorithm

C/No          Carrier-to-Noise density in dB-Hz (e.g., satellite signal quality)

Cs              Cesium (used in atomic oscillators)

CSAC         Chip-Scale Atomic Clock

cTE            Constant (Mean or Average) Time Error

DOCXO      Double-oven OCXO

DNU          Do Not Use

dTE           Dynamic Time Error

E2E           End-to-End Path Delay Calculation Method

EEC           (Synchronous) Ethernet Equipment Clock

ePRTC       Enhanced Primary Reference Time Clock (ITU‐T G.8272.1)

ESMC        Ethernet Synchronization Messaging Channel (ITU-T G.8264)

eSyncE      Enhanced Synchronous Ethernet

FTS           Full Time Support (ITU-T G.8275.1)

FPC           Floor packet Count

FPP           Floor Packet Percentile (FPP Limits are defined in ITU-T G.8261.1 as 1% of packets within 150 µsec of floor delay in every 200 sec period)

FPR           Floor Packet Rate 

Galileo      European GNSS

GLONASS  Globalnaya Navigatsionnaya Sputnikovaya Sistema, Russian GNSS

GM            Grandmaster clock

GNSS        Global Navigation Satellite Systems (generic for GPS, GLONASS, Galileo, Beidou, etc.)

GNSSDO   GNSS-Disciplined Oscillator

GPS          Global Positioning Satellite system, USA GNSS

GPSDO     GPS-Disciplined Oscillator

gPTP        generalized Precision Time Protocol (IEEE 802.1AS)

IED          Intelligent Electronic Device (Power Utilities)

IEEE         Institute of Electrical and Electronics Engineers (Standards body)

IP            Internet Protocol (Layer 3), IP address

IPG          Inter-Packet Gap

ITU-T       International Telecommunication Union, Telecommunication Standardization Sector

LOS          Line of Sight (GNSS RF signals)

LPF           Low-Pass Filter

Layer 2    Ethernet MAC sublayer (switches). Provides flow control and multiplexing for the transmission media.

Layer 3    IP Layer (routers). Provides routing capabilities across network boundaries.

MAC         Media Access Control, MAC Address (Ethernet)

MAC         Miniature Atomic Clock

Max|TE|   Maximum time difference between DUT and the reference

MTIE        Maximum Time Interval Error

NE            Network Element

NTP          Network Time Protocol

OC            Ordinary Clock (Master/source or Slave/destination device with single network connection)

OCXO       Oven-Controlled Crystal Oscillator

Offset       Error, deviation from the ideal frequency or time

OWD         One-Way Delay (end-to-end latency)

P2P           Peer-to-Peer Delay Calculation Method

PDV           Packet Delay Variation (ITU-T G.8260 Appendix I defines a number of metrics that may be used for PDV analysis)

PEC           Packet-based Equipment Clock

Phase        Relative time difference between two 1PPS signals

PNT           Positioning, Navigation and Timing applications

ppb           Parts per Billion (1.00E-9), frequency error or uncertainty (offset)

ppm          Parts per Million (1.00E-6), frequency error or uncertainty (offset)

ppt            Parts per trillion (1.00E-12), frequency error or uncertainty (offset)

PRC           Primary (frequency) Reference Clock (ITU‐T G.811)

Profile       Set of definitions, settings and functionalities that fit an application.

PRS           Primary Reference Source (see PRC)

PRTC         Primary Reference Time Clock (ITU-T G.8272)

PSN           Packet Switched Network

PTP           Precision Time Protocol (IEEE 1588 2008/2019, ITU-T G.8275.1, G.8275.2)

PTS           Partial Timing Support

QL             (clock) Quality Level (ITU‐T G.781, for PTP Clock Class refer to G.8265.1 and G.8275.1)

Rb87         Rubidium (used in atomic oscillators)

RTD           Round-Trip Delay

SC             Slave Clock

SSM           Synchronization Status Message (ITU-T G.707)

SSU           Synchronization Supply Unit (TDM)

SVN           Satellite Vehicle Number

SyncE        Synchronous Ethernet (ITU-T G.8261, G.8262, G.8264)

T1              GM departure timestamp for outgoing Sync messages (one-step: carried in the Sync message itself, or two-step: carried in the Follow_Up message)

t2               Measured arrival timestamp for the Sync message, at the T-SC

t3               Measured timestamp of Delay_Request message departure from T-SC

T4              GM arrival timestamp for incoming Delay_Request messages, sent inside the Delay_Response message

TAI             Atomic Time (Temps Atomique International), PTP time

T-BC           Telecom Boundary Clock (PTP aware switch) ITU-T G.8273.2

T-BC-A       Telecom Boundary Clock for Assisted partial timing support

T-BC-P       Telecom Boundary Clock for Partial timing support

TC              Transparent Clock (PTP aware switch)

TCXO          Temperature-Compensated Crystal Oscillator

TDEV          Time Deviation

TDM            Time Division Multiplexing (networks) such as SDH/SONET, PDH/DSn

TE               Time Error, relative to a standard time reference. (TE = cTE + dTE)

TE1             Forward (Sync) Time Error

TE4             Reverse (Delay_Request) Time Error

T-GM          Telecom Grandmaster Clock (precision time server)

TIE             Time Interval Error

TLV             Type, Length, Value (message fields)

ToD            Time of Day label identifying the last 1PPS pulse (YYYY-MM-DD hh:mm:ss)

T-SC           Telecom Slave Clock (client)

TSN            Time-Sensitive Network/Networking

T-TSC         Telecom Time Slave Clock (time-oriented client)

T-TC-P        Telecom Transparent Clock for Partial timing support

T-TSC-A      Telecom Time Slave Clock for Assisted partial timing support

T-TSC-P      Telecom Time Slave Clock for Partial timing support

UDP            User Datagram Protocol (Layer 4)

UTC            Coordinated Universal Time

VCXO         Voltage-Controlled Crystal Oscillator

XO             Xtal (crystal) Oscillator. (e.g., Quartz)