CSIR-National Physical Laboratory (CSIR-NPL), India’s National Metrology Institute, is responsible for generating and disseminating Indian Standard Time (IST) traceable to Coordinated Universal Time (UTC). To support nationwide synchronization, CSIR-NPL employs multiple time-transfer technologies, including NTP, FonOclock, PTP, White Rabbit, CVGNSS, and TWSTFT. This paper focuses on the design, deployment, and evaluation of cost-effective, Network Time Display (NTD) systems to maintain accurate time across distributed infrastructures using NTP time synchronization. Three deployment models are proposed to address varying institutional needs: direct NTP synchronization, centralized control with Python-based automation, and local NTP server configurations. A real-world deployment at CSIR-NPL demonstrates the system’s functionality, featuring an automated synchronization and alert mechanism developed in Python. Experimental results show a typical RTC drift of 2.65 s per day, with an optimal resynchronization interval of 54 min. A Type B uncertainty budget analysis yields a combined uncertainty of ± 0.622 s (95

Time synchronization is essential for Internet of Things (IoT) and edge computing applications that require accurate time stamping and coordinated operation. Low-cost edge devices employ quartz-based oscillators, which exhibit clock drift over time and Network Time Protocol (NTP) is widely used to mitigate this kind of drift and synchronized to the reference clock. However, achievable NTP synchronization performance is strongly influenced by network conditions and the geographic location of the reference time server. This article presents a study over long period of NTP-based time synchronization on a low-cost edge device, i.e., Raspberry Pi using chrony and geographically distributed NTP servers. Clock offsets and round-trip network delays are recorded at one-minute intervals using chrony tracking statistics, resulting in independent datasets for each server. The collected data are analyzed for evaluating synchronization accuracy, stability, and client-side synchronization uncertainty under realistic network conditions. Client-side uncertainty evaluation has been done for the practical measure of synchronization reliability as experienced by an edge device. The uncertainty analysis also offers a realistic basis for relative performance assessment and informed NTP server selection in IoT and edge computing deployments.

Atomic clocks (ACs) are the most vital devices used by national standard agencies of a nation in order to maintain a continuous and stable time scale. Errors in the prediction of time by the ACs are caused by external factors called anomalies. Monitoring atomic clocks and detecting anomalies is essential for them to serve their purpose. The present study proposes a machine learning-based time-series approach for detecting anomalies in Indian AC data. A point anomaly has been simulated in the AC data, and a prediction has been made. The anomalies have been inserted into the 52-day phase data from August-September 2019 at the National Physical Laboratory, New Delhi. Development has been done in Jupyter Notebook using Python. Based on the analysis, the outcomes showed that precision was achieved at 0.9643, accuracy at 0.9310, recall score was 0.9643, and F1-score was 0.9643, denoting that the obtained results are higher in the 7th and 8th clock, which proves that the developed model is a good fit.

CSIR-NPL is the National Metrology Institute (NMI) of India by an act of parliament. It holds the responsibility to realize, maintain and disseminate the Indian Standard Time (IST), which is traceable to Coordinated Universal Time (UTC) with an accuracy of a few nanoseconds. Dissemination of IST is done via various methods, including satellite links, network time services, and calibration of clocks and oscillators. CSIR-NPL also offers services for delay calibrations of satellite timing receivers and measuring the frequency stability of oscillators. CSIR-NPL has maintained the stack of Network Time Protocol Servers (NTP servers) to disseminate IST over the network. It uses a hierarchical, semi-layered system of time sources. NTP servers at CSIR-NPL are designated as stratum 1 NTP servers as these servers consider their time reference directly from the authoritative time source, i.e. UTC (NPLI). Time synchronization plays an important role in the cybersecurity of the nation by enabling the analysis and correlation of events from multiple sources and reconstructing the sequence of events. It ensures reliable authentication, enhances network security, coordinates actions across distributed components, supports the monitoring and control of critical infrastructure, facilitates compliance and auditing and ensures the proper sequencing and validation of transactions To augment and strengthen the cybersecurity in the country, the Indian Computer Emergency Response Team (CERT-In) has issued a directive to all service providers, intermediaries, data centres, body corporates and government organizations to synchronize their ICT infrastructure to the NTP servers of National Physical Laboratory (NPL), National Informatics Centre (NIC), or accurate and standard time sources other than NPL and NIC. Hence, the performance of stratum 1 NTP servers with respect to UTC (NPLI) is important to evaluate and report in public domain. In this paper, the performance of commercially available NTP servers at CSIR -NPL which holds the designation of stratum 1 in the network hierarchy is evaluated with respect to UTC (NPLI). The time offset of the stratum 1 NTP server with respect to the UTC (NPLI) in the laboratory is analysed and reported. The study explores the time synchronization behaviour of stratum 1 NTP server, which may be useful for organizations which are taking time synchronization services from stratum 1 NTP servers which are responsible for nation-wide time synchronization.

For Indian users, NavIC, the regional navigation system, is designed, developed, deployed, and maintained by ISRO to provide precise positioning and timing services throughout the service region. Geodetic grade NavIC-enabled receivers provide 1PPS timing output together with the position solutions, but the reports on the timing capabilities of such geodetic grade receivers are minimal. In this work, a NavIC L5 and S-band enabled geodetic receiver’s timing performance is studied extensively at CSIR-National Physical Laboratory (CSIR-NPL), New Delhi, India, with access to the standard time scale (UTC(NPLI)) and frequency signals. The NavIC receiver’s timing performance is studied by feeding the external 10 MHz in addition to its unaided operation. The standard deviation of the offset between the time output of the receiver and UTC(NPLI) in unaided operation lies below ten ns, which is sufficient for many timing applications while using the external 10 MHz frequency input to the receiver, sub-nanosecond standard deviation is observed, that will be useful for more stringent timing applications using NavIC. This paper also proposes a novel scheme to link the NavIC time of a remotely located geodetic NavIC receiver to the UTC(NPLI) using the Indirect-PPP timing technique. The concept is explained in detail and validated through experiments. The encouraging results on the NavIC timing offered by geodetic receivers and the Indirect-PPP method would help popularize NavIC timing among the common users.

Accurate time synchronization is a key requirement in today’s digital world. Considering the distributed deployments, it is important that all the devices and systems of digital infrastructure like servers, computers, network devices, Internet of Things (IoT) devices, etc., remain synchronized and work in unison. The Network Time Protocol (NTP) plays a crucial role in making this possible, ensuring consistent and reliable time across devices over the network/Internet. To handle a high number of time requests and maintain dependable service, organizations often run multiple NTP servers. In such cases, it becomes essential to make sure all these servers are precisely synchronized and providing correct time to the end users. There are many public NTP servers accessible freely on the Internet; however, ascertaining timing accuracy and avoiding any anomalous behaviours at the user end is a critical task. Anomaly detection techniques enable early identification of deviations from usual behaviour, allowing proactive mitigation before issues escalate. This paper presents a simple yet effective prototype for detecting anomalies in NTP servers’ data. The approach is based on analyzing NTP packets received at a remote system; therefore, no special access or privileges are required on the NTP servers under observation, beyond standard NTP message exchange. A Python script is developed to collect key metrics from NTP packets. The system pre-processes the NTP packet exchange data and uses statistical analysis methods and machine learning technique (Isolation Forest) to spot any abnormal patterns. The work shows promising results, making it a useful tool for improving service reliability. The work may be enhanced with implementation of advanced machine learning methods and consideration of additional parameters.

Time synchronization is a critical aspect of computing and communication systems. Network Time Protocol (NTP) is the most widely used time synchronization protocol globally for devices on computer network and Internet. This work considers analysis of NTP packets from various prominent NTP services like 'time.nplindia.org', 'samay1.nic.in', 'samay2.nic.in', 'ntp1.npl.co.uk', 'ntp.nict.jp' and 'time.nist.gov'. The analysis is based on capturing NTP packets for same time period from two distinct locations in India separated by around 2500 Km by road. A software is developed for capturing and extracting information from NTP packets received from various NTP servers. The time offset and the delay variations are analyzed in detail. The analysis provides a thorough understanding of NTP synchronization, highlighting its robustness and global timekeeping capabilities. Further, this work can enrich the comprehension of NTP service selection and their implications for diverse applications.

GNSS receivers provide direct and easy access to the UTC through its hardware 1PPS output. Despite the widespread use of geodetic GNSS receivers, more studies are needed on their timing performance. A campaign mode exercise was conducted with a geodetic GNSS receiver in GPS-only mode to address this gap. The experiment was performed in two modes- without and with an external standard frequency fed to the receiver to study its impact on the performance. The impact of a stable oscillator has been observed by the appreciable improvement in frequency stability of the GNSS time with respect to UTC(NLPI). Though notable improvement in standard deviation is observed with the external reference frequency, the performance in the other mode was within a limit of 10 ns; such results are not reported earlier. Further, this paper proposes a novel method of evaluating the delay of the hardware 1PPS during its derivation from the internal time solution from the measured pseudo ranges. The delay is 30.6 ns for this receiver, though depending on its internal circuit arrangement, it may vary across receivers. Understanding this delay would be crucial for specific timing applications. The importance of finding the delay is explained through a notional application.

Precise time and frequency signal transfer over White Rabbit Precision Time Protocol (WRPTP) based underground optical fibre link has been experimentally demonstrated for its potential enhancement and better signal integrity. In order to prove its advantages in practical applications, the time synchronization performance of WRPTP-based underground telecommunication optical fibre links have been examined in controlled environment conditions as well as in varying ambient conditions. Under controlled environment conditions, time synchronization has been achieved within +/- 100 ps uncertainty but variation in ambient conditions degrades the stability as well accuracy of the time transfer link. The introduction of active phase variation compensation enhances the accuracy by similar to 66 % of the WRPTP-based underground time transfer link. The link's instability in terms of Modified Allan deviation reaches to 2.0 E -15 from 7.5 E -15 at 4096 s of integration time which indicate that dynamic phase variation compensation improves the stability of WRPTP-based time transfer link under varying ambient conditions.

With large-scale Cyber-Physical Systems (Internet of Things) deployments, the low-cost networked devices are becoming ubiquitous. Time stamping of events is a basic requirement and it is crucial for distributed/isolated systems/devices to work in unison. The system clocks of these devices are not very stable and their behaviour is affected by ageing and environmental conditions. A clock's timing behaviour is generally analysed independently by comparison to a highly stable standard reference clock using specialized instruments. Network Time Protocol (NTP) is widely used for time synchronization over computer networks. As the NTP server clock is more stable in comparison to a client's system clock, the variation in the end device's clock offset values with respect to the NTP server clock over a long time can be considered for analysing the behaviour of the end device's clock. This paper presents a method for analysing clock behaviour based on NTP messages. A computer programme is developed, which utilizes an open-source NTP client library to exchange NTP messages and records end device's system clock's offset variations over time for a given periodicity to analyse the behaviour. This black box analysis approach does not require any direct access to the end device's clock circuit. The solution may be useful for analysing clock behaviour for long-term stability under actual environmental conditions, for deciding time synchronization periodicity to optimize the number of synchronization packet exchanges, and for pre-deployment timing stability assessment of devices for deployment scenarios having intermittent/non-availability of periodic time synchronization.

In this paper, a proof-of-concept experiment for IEEE1588 PTP-based Indian standard time dissemination through a dark telecom optical fiber in the central Delhi region has been reported. This is the first such demonstration of IST through terrestrial optical fibers and should provide redundancy to popular satellite based time distribution in India.

The article presents the work on the effect of temperature on time transfer through optical fiber link and the comparison between two different lengths, i.e., 300 m and 30 km of fibers. We observed more than 200 ps offset arising during 68 days of measurement.

Network Time Protocol (NTP) servers are specialized timekeeping devices that provide synchronized and accurate time information to networked devices, ensuring precise coordination and reliability in various critical applications. CSIR-NPL is the National Metrology Institute of India which has the responsibility of time dissemination to the nation. Network time dissemination is one of the services which provide the time synchronization facility over the network via NTP servers. These NTP servers are designated as stratum 1 NTP servers in the network hierarchy as they are taking time from the authoritative atomic clock. NTP servers at CSIR-NPL are available in public domain for time dissemination. Many critical stakeholders such as internet service providers, data centres, various government organizations are the primary customers of CSIR-NPL for time services over the network. Hence, to understand the traffic dynamics coming towards the NTP servers is essential. This study aims to analyze Ethernet traffic patterns directed towards NTP servers at CSIR NPL using open-source monitoring software, i.e., Zabbix and Grafana. The study captures Ethernet traffic throughput in bits per second (bps) coming on NTP servers located at CSIR-NPL. These NTP servers are part of stacks of NTP servers responsible for disseminating Indian Standard Time over the internet. The study involves an investigation of Ethernet throughput to understand the NTP requests (packets per second) arriving for time synchronization and the pattern of incoming NTP request traffic on these servers. To evaluate NTP requests from Ethernet throughput, the conversion of Ethernet traffic from bps to packets per second (pps) is done and validation of the captured Ethernet throughput with actual traffic values obtained from the OEM software is accomplished. The investigation further explores incoming NTP traffic patterns and identifies regions where traffic reaches maximum and minimum loads, as well as its respective peaks and troughs, utilizing 5-day Ethernet datasets. The Savitzky–Golay filter is employed for data smoothing, and the gradient of the smoothed data is calculated to determine distinct regions of the traffic pattern. The results provide a comprehensive understanding of the traffic behaviour directed towards NTP servers for time synchronization, enabling the monitoring of anomalies associated with cybersecurity and contributing to the optimization of network resource allocation.

With the advent of time sensitive innovative applications under the Internet of Things and Industry 4.0 landscape, timing accuracy requirements have become crucial. Many current areas, like telecommunications, smart grids, the stock market, intelligent sensors ecosystems, etc., require timing accuracies in milliseconds to microseconds. The upcoming applications will require even more precise timing synchronization. For time synchronization, industrial applications are considering various approaches based on satellite or network-oriented techniques. These techniques are unique in terms of their functioning and pose unique challenges regarding their applicability. For example, Global Navigation Satellite System (GNSS) based time synchronization can provide nanosecond-level accuracy; however, the accessibility of satellite signals in indoor and other scenarios is a challenge. Distributed systems, like sensor networks, vehicular ad-hoc networks, distributed clouds, and many smart technologies under the umbrella of Industry 4.0, pose their unique challenges for time synchronization. The paper presents timing accuracy requirements for different application scenarios and discusses the suitability of available timing technologies to support them. It discusses the applicability and constraints of different technological solutions and explores new research directions in the area.

In this paper, Indian Standard Time (IST) Dissemination Technique and synchronization method over different network architecture and their respective delay measurements have been presented. Presently, one of the robust terrestrial time dissemination method over the network is via Network Time Protocol (NTP). CSIR—NPL as the time keeper of India, is disseminating IST in public domain through NTP servers which can be accessed by the users with domain names “time.nplindia.in” and “time.nplindia.org”. These NTP servers have been synchronized with primary atomic time scale through 1pps external input and attain stratum1 status in network hierarchy for IST dissemination services. Authentic delay measurement is required for synchronization of another NTP server over the network for reliable time dissemination service to the users. The work presented in this paper is toward the authentic IST dissemination measurements via the NTP servers. In this experiment, a NTP server has been synchronized with the stratum-1 server and time delay has been measured for a period of 36,000 s over different network architecture viz. direct link network, hybrid link network and wide area network. Since CSIR—NPL is working toward the nationwide legalization of IST, this experimental analysis will strengthen the confidence in building authentic and reliable IST dissemination infrastructure via NTP servers in the nation.

An atomic clock drifts from UTC (Coordinated Universal Time) due to factors such as aging and frequency drift. Algorithms are designed to provide a stable timescale by predicting and steering clocks to standard reference time (UTC). Kalman filter is an optimal estimator that can estimate present and future behavior of an atomic clock with respect to a stable reference timescale. A clock in general comprises white phase noise, white frequency noise, random walk frequency noise, random walk frequency aging, and constant frequency aging. Kalman filter is required for removal of noises and improving clock performance. The role of Kalman filter in improving the long- and short-term stability of a free running clock is investigated. A state matrix is formulated using a phase difference and frequency of clock with respect to a reference signal in this algorithm. The estimated state from Kalman is further used in a control algorithm for steering of clocks. Steering removes the drift in atomic clock and generates an accurate clock output with respect to UTC. The level of steering is determined by user-defined parameters. The variation in steering coefficient leading to a change in clock performance is studied.

Present definition of SI second is based on the hyperfine transition frequency (in the microwave region) in Cesium atoms since 1967. In the last two decades, frequency standards based on optical transition have shown remarkable progress by outperforming the best microwave frequency standard by at least an order of magnitude in terms of relative frequency uncertainty. This paper presents an insight on the present realization of a microwave SI second and the roadmap towards future realization based on optical transition frequencies.