Indian Standard Time

Indian Standard Time

By: P Arora, M P Olaniya, P Kandpal, S Yadav, V Bharath, T Bhardwaj, P Thorat, S De, S Panja, N Sharma, A Agarwal, V N Ojha and D K Aswal, The authors are from the department of Time and Frequency Standards, CSIR- National Physical Laboratory, New Delhi.
Indian Standard Time is the primary reference on which the country runs. However, keeping time is not the simplest of jobs. CSIR-NPL ensures that this time becomes accessible to all and everything runs proverbially, like clockwork.
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Metrology is the science of measurement which involves the study of weights and measures of various quantities and units. With continual and long-term R&D efforts in science and technology, the International System of Units (SI) has evolved as a unified modern metric of measurements. SI system, involving base (independent) units (metre, kilogram, second, kelvin, candela, ampere, mole) and derived (dependent) units help in ensuring that reliable measurements give reproducible (same) results whenever and wherever they are made. A metrological standard is a perfect realization of the fundamental unit with highest possible accuracy. Primary standards of a quantity are made for each unit and are maintained by the National Measurement Institute (NMI) in each country. All working standards should be calibrated with respect to the primary standard to obtain reliable measurements.

The metrology of time involves the continuous measurement of counts of a periodic event. Any clock consists of a frequency source (oscillator), a counter and a display. The quality of any clock depends on its oscillator and the quality of an oscillator is defined by its accuracy and stability. A second (s) is the basic unit for measuring time. The second multiplied evenly by 60 gives us a minute and when multiplied by 3, 600 it gives us an hour. The length of days, and even years, is measured by the basic unit of time, the second. Time intervals of less than a second are measured in l0ths, 100ths, 1000ths-on down to billionths of a second and even smaller units. In India, CSIR-National Physical Laboratory is mandated through an act of the Parliament (Govt. of India Gazette No 589) for realisation, establishment, maintenance and dissemination of seven base units including Indian Standard Time (IST). CSIR-NPL, internationally known as NPLI and the Timekeeper of India, has the Primary Reference Clock, which is traceable to the Coordinated Universal Time or Universal Time Coordinated (UTC) provided by International Bureau of Weights and Measurers (BIPM) located in Sevres, France. CSIR-NPL is also responsible for making the second—the standard unit of time interval—available to many thousands of time users everywhere in India—not only on the land, but to ships at sea, planes and satellites in the air, and deep space vehicles in outer space.

History of Indian Standard Time

India is the seventh largest country in the world, extended from 8o 4’ 28” N to 37o 17’ 53” N along the latitudes and from 68o 7’ 53” E to 97o 24’ 47” E along the longitudes encompassing 3,214 km from North to South and East to West distance it is 2,933 km. With approximately the same latitudinal and longitudinal extent—about 30o, India falls under a single time zone, five and a half hours ahead of UTC, i.e., UTC+5:30, known as the Indian Standard Time (IST). It is the official time of India maintained by CSIR-NPL. The IST line is corresponding to longitude 82.5o E near the Shankargarh Fort in Mirzapur (25.15oN, 82.58o E), Uttar Pradesh.

Under British rule, the meridian passing through 82.5o E longitude was chosen as the central meridian for India but was not adopted as the official time zone. It was only in 1947  that IST was officially established. In 1945, CSIR-NPL was established as a standards laboratory, a national metrology institute, designed to offer national standards for physical measurements. Later on, CSIR-NPL was given the mandate to establish, maintain and improve continuously by research, for the benefit of the nation, National Standards of Measurements and to realise the ‘Units’ based on International System by an Act of Parliament under the Standards of Weights and Measures Act of 1956 and 1976,  (and the Rules of 1988) and the Legal Metrology Act 2009, (under the rules of 2011). CSIR-NPL is maintaining the second, the unit of time interval (difference of time between two events) in the International System (SI) of units. In 1974, CSIR-NPL acquired its first atomic clock and enhanced its time keeping capability by about 10,000 times than before. Since then CSIR-NPL is contributing to the International Atomic Time (TAI; TAI from the French name temps atomique international) and locally realising the UTC to generate Indian Standard Time. This was only the beginning of contemporary time keeping. CSIR-NPL is also involved in adopting the latest technologies periodically to maintain its global standard and also pursue state-of-the-art research for indigenisation of the most accurate atomic clocks. At present CSIR-NPL is well equipped with about eight ceasium atomic clocks and four active hydrogen masers, which constitute two time scale systems to uninterrupted dissemination of IST throughout the country.

Realisation of UTC and Indian Standard Time

CSIR-NPL is responsible for the highest level of time and frequency measurements in India, maintenance and dissemination of Indian Standard Time and keeping it traceable to the International organizations including BIPM.

Indian standard time is realised through an ultra-stable and precise timescale maintained at the main building of CSIR-NPL. A time scale is defined by a starting point and is thereafter continuously accumulated in time units, where these time units are defined as time intervals. For example, the SI unit of time is a second, which accumulates and then transforms into minutes, hours, days, weeks, months, years, etc. A second is defined as the time that elapses during 9192631770 cycles of the radiation produced by the transition between two ground state levels of laser cooled Cesium (133Cs) atoms.

International Atomic Time, TAI, is the coordinated reference time established by the BIPM at Paris and it is not a physical clock. It is a system time or a paper clock, calculated using more than 450 clocks in approximately 75 laboratories around the globe as a weighted mean value. UTC is also derived from atomic time, but its time is adjusted by 1 second after a certain time to keep it in phase with Universal Time, UT, which is based on the Earth’s rotation around its own axis. CSIR-NPL maintain a timescale to realises its local UTC, known as UTC (NPLI).

The present timescale consists of five high performance caesium clocks, one active hydrogen maser and these are contributing to TAI and at present the time and frequency traceability between CSIR-NPL and BIPM is maintained with Common View Global Navigational Satellite System (CVGNSS) links.  CVGNSS is one of  the most commonly used and accurate methods of time transfer or clock comparison among multiple users. In this method two stations receive time signals transmitted from a single source—GPS or GLONASS. Both stations compare their time signals with respect to a particular signal that arrives at their respective locations from that common source. The stations then compare these measurements and subtract them with a reference station. If the one-way path delays from the transmitter to  both stations are nearly equal, then both the delay and the characteristics of the transmitter cancel in the difference, so that the time difference between the two receiving sites can be computed without knowing anything about the source or the path delay. The schematic of the traceability link among the NMIs with BIPM has been shown in Figure 1.

CSIR-NPL also provides time and frequency traceability link and disseminating Indian Standard Time to different sectors within the country using different advanced technologies like two-way satellite time and frequency transfer (TWSTFT) and CVGNSS.

Dissemination of Indian Standard Time

CSIR-NPL provides Indian Standard Time to users via different techniques, as depicted in Figure 2. The most common dissemination technique is through  the internet and it is done using NTP servers installed at CSIR-NPL which are synchronised to Indian Standard Time. The typical uncertainty of time via NTP is a few hundred milliseconds. At other times dissemination technique works via telephone lines and is called FonOclock. FonOclock transmitters are synchronised to Indian Standard Time and connected to telephone lines. Users having FonOclock receivers can access Indian Standard Time via this service with a typical uncertainty of ±10 ms. The most accurate dissemination is done through satellites. CVGNSS is able to provide time with an uncertainty and is best for the strategic sectors. Work is underway to have more dissemination methods such as precision time protocol (PTP) and even through long-wave radio to ensure synchronising the whole country within 1 s of Indian Standard Time. A recent scientific study done by CSIR-NPL has suggested that India needs two time zones IST-I (UTC+5:30 h) and IST-I (UTC + 6:30 h) with demarcation at longitide 89052’E. (Sharma, 2018).

Applications of Precise Time

Accurate time synchronisation and stamping is essential in several sectors in order to harmonise and deal with any legal issues. For example:

  • In strategic sectors, surveillance, accurate targeting, satellite launching and their placement in the right orbits, space application and astronomical research, all rely on precise time measurement and synchronisation. Inaccuracy of even one nano-second leads to a spatial error of several meters. ISRO, DRDO, the Air force, the astronomical observatories (GMRT, ORT) currently rely on accurate time synchronisation by CSIR-NPL.
  • In navigation time synchronisation of onboard clocks with base receivers and transmitters is essential for pin pointing the position of
    an object.
  • All financial transactions require accurate time stamping for fraud protection. Accurate time stamping to the banking sectors is provided by  the Controller of Certifying Authority (CCA) through CSIR-NPL’s teleclock service.
  • An efficient stock market is a non-negotiable requisite for any country’s financial health and accurate time stamping forecloses ambiguity and associated financial losses.
  • Digital archiving: Storing data in an orderly manner is important for efficient operation of trade or any other sector which has multiple branches. An error in time can cause significant problems and even include legal liability.
  • Time sychronisation is also essential in safeguarding national security through situation monitoring and responses as well as having an alarm mechanism. Moreover, synchronisation of network devices also ensures cyber security, tracking and identifying breaches and crime, where needed.
  • From routine weather prediction to being forewarned against natural disasters through dynamic mapping, no associated device can do without time synchronisation.
  • In disaster management, both in the case of natural phenomena and anthropogenic situations, it carries vital importance in providing early warnings right down to post hoc relief.
  • Accuracy is also crucial for civil infrastructure where it is employed for power grid maintenance and, in particular, transportation where signalling and navigation cannot dispense with it.

Financial Sector

The saying ‘time is money’ could not have been more apt. Time stamping is very important in the financial sector, notably in high frequency trading that uses complex algorithms. India has seven stock exchanges, five Commodity Derivative Exchanges and an International Exchange (INDIA-INX). IndiaINX is the world’s fastest stock exchange with a round trip latency of 3μs for executing an order. Next comes the Bombay Stock Exchange (BSE) with 6μs latency followed by Singapore stock exchange with 16μs latency.To understand what this 6μs latency means to the BSE is that it has a capability to executive upto 6 lakh orders per second i.e., buying and selling shares, editing, reviewing or cancelling orders etc.

Trading in the share market takes place on the basis of a ‘time place priority’. Hence, accuracy of time is all important for trading shares and commodities. Every order placed in the stock exchange takes place through a registered broker of the stock exchange on behalf of the trader. Some exchanges provide space within their premises to brokers for setting up high speed servers with algorithms that give an advantage of fraction of a second.

The European Union has brought regulations for its financial markets for high frequency trading where every transaction has to be time stamped with ±1μs latency with reference to the UTC from January 3, 2018 and also guided implementation of block chain technology for transparency. Likewise, the USA came up with the guidelines for a latency of ±50ms latency with reference to NIST (National Institute of Science & Technology) standard time for any financial trading transaction which are implemented from February 20, 2017.

In India SEBI (Securities and Exchange Board of India), the regulatory authority of securities market  directed on March 30, 2012 to synchronise the system clock of the stock exchange with the atomic clock before start of the market with 1μs precision and ±1ms accuracy.

Not only is accuracy important, but traceability is just as important. If different trading machines are traceable to different reference time sources (different NMI’s like NIST, Indian Standard Time, GPS, Galelio etc.,), then it is called relative time stamping, unhelpful in forensic analysis of fault which happens within a latency of micro seconds.

Recent reports carried a whistleblower’s allegation that two stock brokers were given unauthorised access a little before the National Stock Exchange (NSE) opened for trading to  the tune of INR 50,000 crores (Financial Chronicle, 2018). It was very difficult for the third party company which is doing the forensic analysis of the scenario to get the exact details of the transactions due to lack of proper protocol and guidelines for high frequency trading (Ray, 2018).

As India’s finance market is worth around INR 15,00,000 crores, robust regulations for algorithmic and high frequency trading are an inescapable requirement. Since certainly every person in India is directly or indirectly synchronised to Indian Standard Time, clocks of the trading machines  should also be synchronised with
the same.


Atomic clocks in GPS satellites keep time to within three nanoseconds—three-billionths of a second. Position accuracy depends on the receiver. Most handheld GPS receivers are accurate to about 10 to 20 meters.

Both military and civilian users can obtain higher accuracy by using a second GPS unit at a fixed nearby location—a method called differential GPS. In this way, positions can be determined with an accuracy better than 1 cm. For military users, additional encrypted signals can provide high accuracy.

All GPS satellites transmit their data signals at the exact same time, with precise synchronisation. Their signals are monitored constantly and adjusted as needed.


In telecommunication, various service providers use an independent time synchronisation solution for their network. But it is not an uncoordinated activity. Time also differs for the same service provider in the case of operations in different time zones. Therefore, the reference needs to be the same.

As public IP is limited, the same IP is allocated to multiple customers located at different points of time using the network translation technique (NTA). But in order to identify different customers, it is very important that the logs are maintained by telecom and internet service providers. Asynchronous functioning might result in a gap in cyber security and present difficulties for law enforcement.

Time synchronisation is also consequent to the quality of service as in VoIP (Voice over Internet Protocol), where accurate server and router log files are essential to IP telephony reliability. Every log file entry is time stamped to establish the time of events and facilitate the sequencing. Different hosts contribute to form a collective log file of the server. Hence it is important that the time stamps are precise. Failing this, troubleshooting root-cause problem will be impossible and the VoIP network operation will become impossible. Uncoordinated time sync between telecom and ISP operators results in frame loss, handover failures, loss of voice quality etc.

Cyber Security

Cyber security is a term that refers to the protection of resources connected over internet from cyber attacks. These resources include hardware, software and data. When we deal with computing context, security concerns both cyber security and physical security and critical assets have to be protected from unauthorised access.

Another widely used term is information security: a subset of cyber security dealing with maintaining the confidentiality, integrity and availability of data.

Cyber security can help prevent cyber attacks, data breaches, identity theft, and also aid in risk management. The most common kind of attacks which are familiar to all includes:

  Malware Attacks,

  Phishing Attacks,

  SQL Injection Attacks (SQLi),

  Denial-of-Service (DOS) Attacks,

  Distributed -Denial-of-Service (DDOS) Attacks.

Time synchronisation becomes critical because every aspect of managing, securing, planning, and debugging a network involves determining when events occur in terms of cyber security. Without synchronised time, accurately correlating log files between these devices is difficult, even impossible.  Time is often the critical factor that allows an event on one network node to be mapped to a corresponding event on another.

The financial services (Banks, Stock exchanges etc.) require highly accurate timekeeping. The Armed Forces require time accuracy in the time of war and strategic operations. A dedicated network time protocol server is essential for protection against cyber security risks. As more and more devices are coming up on the Internet architecture, the necessities of time synchronisation between these become crucial. In order to design a framework that embraces IOT devices and things in a synchronized fashion over time , it becomes very essential that a uniform time stamping should be there on all communications happening over real and virtual world. It was in this context that it was proposed that CSIR-NPL that fulfills the primary responsibility of maintaining the standards of basic SI units also disseminates Indian Standard Time to all the sectors with their various branches all across the length and breadth of the country.

In this context, everything needs to be on Indian Standard Time with final traceability to CSIR-NPL where stratum 0 (the primary standard of Indian Standard Time) is maintained via an assembly of atomic clocks. In order to seamlessly synchronise these sectors over the internet, a new architecture needs to be developed that not only takes care of cyber security aspects but also works on the upcoming IP6 architecture where each device interacting over internet has its  unique IP address.

Therefore, the nation’s timekeeper, CSIR-NPL has recently embarked on a national mission to synchronise all the device clocks in the country to Indian Standard Time for increased cyber-security through accurate traceable time-stamps. This will result in enhanced overall economic growth.


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