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Australian Government: National Measurement InstituteAustralian Government: National Measurement Institute
National Measurement Institute

Time and Frequency Dissemination Service

NMI provides the following time and frequency dissemination services:

  • GPS time-transfer via an NMI-developed system
  • GPS integrity monitoring
  • Network Time Protocol (NTP) service via a national network 
  • telephone dialup service for synchronising computers 

Click here for information on our time and frequency standardscalibration servicesresearch and the operation of radio clocks in Australia

For further information contact or tel: +61 2 8467 3501.

GPS Time-transfer System

NMI's GPS time-transfer system offers a solution for time and frequency laboratories requiring a reliable and adaptable multi-channel strict common-view GPS receiver which generates standard CCTF-format data files. The system combines the reliability of a commercial GPS timing receiver with data-logging and processing software operating on a standard PC running under the Linux operating system. Features of the system are:

  • Reliability — more than 30 NMI GPS time-transfer systems are currently in operation throughout Australia and the Asia-Pacific, including some in national laboratories overseas. These systems have demonstrated high reliability over many years of field operation.
  • Remote operation — the systems can be operated remotely, including data access, via a dialup or Internet connection.
  • Standard CCTF format data output — output from the receiver is processed and reported following BIPM's standard for GPS time receiver software. A full description of this standard can be found in DW Allan and C Thomas, Technical Directives for Standardisation of GPS Time Receiver Software, Metrologia 31, 69–79, 1994.
  • Extendable hardware — the systems can be expanded to include extra GPS receivers, other time signal receivers, distribution amplifiers, a built-in rubidium atomic frequency standard, and/or an uninterruptible power supply. The system can also operate as an NTP server.
  • Flexible and multiple GPS common-view schedules — raw timing data is collected for each visible satellite throughout the day and is processed to produce CCTF format data following the BIPM GPS common-view tracking schedule, and/or a custom schedule.

GPS Integrity Monitoring

The integrity of signals received from GPS satellites is monitored and recorded by our time-transfer systems at a number of locations in Australia and the Asia–Pacific region.

Daily files of this data can be found at Select the required location and the data file name format is MJD.html where MJD is the Modified Julian Day.

Daily values of UTC(AUS)–GPS time (as measured at NMI Sydney) are calculated from linear fits over two days, and can be accessed via The file name format is nmimm-yy.gps.

NTP Servers

NMI operates a number of NTP servers across Australia which are traceable to UTC(AUS). To register for this service, email the following information to

  • IP address(es) of the NTP client computer(s) — these addresses must be static; please try to restrict the number of clients to no more than three
  • name, email address and telephone number of the person responsible for the NTP client computer

Our servers will not respond to an unregistered client computer.

Traceability data for our NTP servers may be obtained via our FTP server.

Privacy note
NMI collects contact information so we are able to notify users of changes to the service and inappropriate operation, e.g. by polling the servers at excessive rates (this has occurred several times through erroneous configuration and software or firmware bugs and has adversely affected the operation of our service to the detriment of other users).

NMI collects and maintains contact information in accordance with the principles and requirements of the Privacy Act 1988. This information is only used to contact authorised users of our NTP service, and is subject to strict limits on disclosure under Principle 11 of the Privacy Act. It is maintained electronically in a secure database. Authorised users are entitled to review their own contact information as recorded by NMI. You can also raise any concerns with the Privacy Commissioner.

Telephone Dialup Service for Synchronising Computers

If you are unable to access our NTP servers because of network security concerns, we offer a telephone dialup service for synchronising computers which uses the Automated Computer Time Service (ACTS) protocol developed by NIST (USA). For more information go to

To ensure that you are notified of any changes to the service, please contact

The telephone number for this service is 02 8467 3727.

Users outside Sydney are charged at STD rates.
A call lasts about 30 seconds.
The measured time differences are with respect to UTC(AUS) (not NIST as stated by the NIST ACTS client software).