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By law PTB is entrusted with realization and dissemination of legal time for Germany, which is defined as UTC(PTB) plus one or two hours. During the last 24 months, including December 2019, UTC(PTB) did not deviate from Coordinated Universal Time UTC by more than 3.2 ns. The services of dissemination can be grouped in “traditional”, “IT-based”, and “based on data recording and publishing”. “Traditional”: The standard frequency and legal time transmitter DCF77 is still the most prominent part of PTB’s time services. The number of operational receivers in Germany and Europe is estimated to be more than 100 Million. Monitoring of the equipment operated at the transmitter site has been modernized over the years, and PTB is prepared to offer the service for another decade. Contractual negotiations with the operator of the transmitting facilities are going to start in 2020. The number of accesses to the telephone time service remains at a level above 1500 per day with a slight downward tendency. “IT-based”: PTB’s internet time service installations are distributed in two buildings and have been upgraded. Two devices capable to act as PTP Grandmasters have been installed, one at each location, which receive multiple timing reference inputs, and which are mutually monitored. They feed the three publicly accessible network time protocol (NTP) servers which answer about 6000 requests per second and two NTP servers for internal use. At the same time, the Grandmasters represent two Smart Meter Gateway (SMGW) administrator servers for dedicated customers. Since 2019 PTB provides a test bed for a secure NTP time service based on Network Time Security (NTS). Work is ongoing to exploit the enhanced redundancy and fully activate all monitor and control functions. In response to the perpetual popularity of services in the World Wide Web (WWW), PTB offers a service to distribute legal time via the WWW which has been coded in HTML5. It is accessible from the home page of PTB (www.ptb.de) or directly via https://uhr.ptb.de and offers the feature to display the time difference between the local system clock of the calling device and legal time as received from PTB. Via a commercial fiber-optic time transfer system Deutsche Telekom Technik (DTAG) receives signals of UTC(PTB) at sites in Bremen, Hannover, and, particularly, in Frankfurt am Main where UTC(DTAG) is realized. After a recent calibration, the time comparison between the two UTC realizations via fiber and via the GPS common-view method agree well within the calibration uncertainty. “Based on data recording and publishing”: PTB, like other national metrology institutes (NMI), has published regular reports— the so-called “Time Service Bulletins”—on the offset between GPS time derived from the satellite signals and UTC(PTB) for two decades. Since the last update, similar information on Galileo System Time (GST), including the prediction of the offset between UTC(PTB) and UTC(USNO) (via GPS) and UTC (via Galileo), based on the navigation messages of GPS and Galileo, respectively, is given. These reports shall give confidence that the broadcast GNSS signals provide a good approximation to UTC in both frequency and time. Their observance is usually required by accreditation bodies as part of the process of demonstrating traceability of corresponding measurements in accredited calibration laboratories. “Other activities”: In the framework of EURAMET project TF-1156 “GPS link calibrations in support of CCTF-K001.UTC”, PTB continues to offer calibrations of GPS signal delays in receivers of other European NMIs as well as other research institutes. In recent campaigns the institutes NMISA (South-Africa), IMBH (Bosnia-Herzegovina), and DTAG were visited. Campaigns that are ongoing at the time of writing cover NIMB (Romania), SIQ (Slovenia) and VTT (Finland), the latter employing a newly ensembled receiver kit.

On top of positioning, Global Navigation Satellite Systems (GNSS) can be used for time determination and synchronization applications. The European GNSS Galileo is therefore good candidate to offer a dedicated Timing Service, with accuracy, robustness and integrity. In this frame the EGALITE (Galileo Timing Service Extension and Consolidation) project was launched in 2018. The EGALITE project was funded by the EC as part of the Horizon 2020 framework programme and aimed at studying the possibility of developing a EGNSS Timing Service based on Galileo with committed end-to-end performances. The project’s consortium is led by GMV with VVA, Physikalisch-Technische Bundesanstalt and Observatoire Royal de Belgique as partners. The aim of this paper is to provide a summary of the main outcomes of the activities developed in the frame of EGALITE project: • A brief description of the project objectives is provided, including the motivation for developing a EGNSS Timing Service and what is understood by Timing Service. • The integrity capability of the future potential EGNSS Timing Service is addressed including aspects previously mentioned: high-level architecture definition, receiver processing, operational concept, standardisation and certification aspects and Cost Benefit Analysis (CBA) results. • The design of a Legal Time Traceability Service is also proposed in the paper. As will be seen in the paper, we propose EGNSS Timing Services based on Galileo with committed end-to-end performances provided EGNSS Timing Receivers are certified.

Laboratory sources for standard frequency, one pulse-per-second (1pps) ticks, and time-of-day information which receive external time signals to control their built-in oscillators are widely used wherever accurate and stable frequency and time optionally with universal synchronization are required. Nowadays, such devices mostly apply the signals received from the Global Positioning System (GPS), but also signals from alternative Global Navigation Satellite Systems (GNSS), e.g. the European Galileo, or from low frequency transmitters, e.g. WWVB in the U.S. or the German DCF77, are used. The first parts of our paper deal with traceability of measurements of frequency and time pulses to Coordinated Universal Time (UTC) and particularly to UTC(PTB), its realization by the Physikalisch-Technische Bundesanstalt (PTB), using a disciplined oscillator (DO) with standard frequency and 1pps outputs. For this purpose, the role of PTB’s weekly published Time Service Bulletin (TSB) is discussed in detail. The metrological steps for establishing and maintaining traceability are described and uncertainty contributions for both aspects, frequency and time pulses, are discussed. In the last part we discuss how to possibly meet financial sector regulations according to the European MiFID II. We present a procedure as a component for the assessment to provide accurate time through telecommunication networks using e.g. the Network Time Protocol (NTP). Our procedure checks outputs of an NTP server to validate that its 1pps output signal, which is considered as the device’s time reference point, is in accordance with specific requirements and that the provided time-of-day via NTP corresponds to local legal time (modulo integer hours).

The comparison of distant clocks has always been an important part of time metrology. It is important in science in general as well as in everyday applications. Signals from the satellites of the Global Positioning System (GPS) started to be used for the purpose in the early 1980s. This is of course ongoing, and the Time and Frequency Department of Physikalisch-Technische Bundeanstalt (PTB) provides GPS observation data in format RINEX (2.1 and 3.01) and CGGTTS V2E from several receivers on its public ftp-server and to the Bureau International des Poids et Mesures (BIPM). The “golden” reference receiver is still a legacy Ashtech Z12T with the designation PTBB (for RINEX) and PT02 (for CGGTTS) data. PTB also provides GLONASS observation data since a couple of years. Some were used for time comparisons between institutes collaborating with BIPM in the realization of International Atomic Time TAI. At the time of writing, however, no GLONASS data are used for establishing any link in the TAI computation. GLONASS link results are still reported on the BIPM ftp site, e. g. for comparing UTC(PTB) and UTC(SU). In these days, preparations are underway to routinely use signals from the other GNSS that have come to existence. Recently, Galileo and BeiDou have reached a status of early operation phase. In this contribution we thus report on the initial use of Galileo and BeiDou signals in PTB.

GNSS time transfer is a primary method for remote atomic clock comparisons. There are four global satellite navigation systems in operation, named GPS, GLONASS, Galileo and BeiDou. To guarantee the precision, the accuracy and the robustness of Coordinated Universal Time (UTC) generation, multi-techniques strategy has been encouraged by Consultative Committee for Time and Frequency (CCTF) since 2009 for the purpose. In order to realize BeiDou Common-View time comparisons, three GNSS receivers, which can observe BeiDou satellites were installed in the National Time Service Center, Chinese Academy of Sciences (NTSC), and Physikalisch-Technische Bundesanstalt (PTB) has updated two receivers for BeiDou tracking in August 2017. PTB currently is the pivot laboratory in UTC time links. NTSC has about 40 clocks gaining a weight of more than 5-6% of the total UTC clock weight in past years. BeiDou time (BDT) is traceable to UTC through UTC(NTSC). Therefore, it has been a particular motivation to implement time comparisons by BeiDou for the connection between PTB and NTSC. The PTB-NTSC links was established by BeiDou satellites starting in August of 2017 and its time comparison result are within expectations. In order to verify the performance of a BeiDou global service, we also made some preliminary BeiDou time transfer tests between five IGS stations and NTSC.

The recent activities in the field of time and frequency dissemination and applications at PTB resulted in improved quality and a wider reach of the offered services. The basis of these activities remains PTB’s local realization of Coordinated Universal Time UTC(PTB). PTB’s time services comprise the operation of NTP time servers, a telephone time service and the standard frequency and time dissemination by the low frequency transmitter DCF77. The number of requests of the public NTP service approaches 7000 per second. The number of accesses to the telephone service remains steady at about 1800 per day. The standard frequency and time signal transmitter DCF77 is still the most prominent of PTB’s time services. The number of operational receivers in Germany and Europe is estimated to be more than 100 Million. In summer 2016 a calibrated GNSS receiver was installed at the transmitter site. Time comparisons between the caesium clock which serves as the reference for the transmitted signal and UTC(PTB) have since then been made with an uncertainty of 5 ns via GPS and Galileo common view. Time and frequency comparisons with institutes all over the world represent an important part of the activities. PTB continues to be the pivot in all GPS and GLONASS comparisons by which the metrology and research institutes world-wide contribute to the realization of UTC. Data from four different GNSS receivers are regularly provided to BIPM. PTB’s “golden receiver”, a legacy Ashtech ZXII-T (acronym PT02), has been found stable and reliable in the very long term, but shows annual delay variations with a peak-to-peak amplitude of about 1 ns, likely related to the outdoor temperature affecting the antenna cable delay. A possible new reference receiver was identified and is going to be tested before eventually taking over the status of PT02. PTB has accepted the role of a so-called “Group1” laboratory that should offer (in cooperation with BIPM and together with French and Spanish institutes) calibrations of GPS time links to other European NMIs and other research institutes. A so-called G1G2 campaign was finished in August 2016, during which relative receiver internal delays of in total 11 receivers belonging to the institutes DLR, METAS, VSL, and BEV were determined with reference to the PT02 delays determined by BIPM in 2014. Draft results of the 2016 BIPM campaign showed that PT02 delay changes amount to not more than 0.5 ns. A similar exercise using travelling GPS receivers was organized by SYRTE/Observatoire de Paris in the frame of the Galileo Time and Geodetic Validation Facility (TGVF) project managed by GMV, Spain, providing similar results. A TWSTFT calibration campaign was once more undertaken by the U.S. Naval Observatory and revealed the excellent long-term stability of the link between USNO and PTB via TWSTFT. The difference between successive calibration values is at the 1 ns level.