Network Time Protocol (NTP)

 Technical Notes
 Further Information

Daylight saving time changes came into effect March 11, 2007. For information on how this can affect computers, click here.

The Network Time Protocol (NTP) is one of the most accurate and flexible means of sending time over the Internet. It can be used by almost any type of computer. The protocol is designed to compensate for some, but not all, network time delays between the server and the client. NTP is most successful across local area networks and can give accuracy as good as a few milliseconds. On the world wide web however, time transfer delays are at the mercy of server traffic and network bottlenecks, and accuracy figures cannot be quoted as easily. In addition to NTP, NRC offers more accurate time transfer services, other than by internet. Contact us with your requirements.

NTP conveniently supports security measures for users who want more reassurance concerning the origin of the time stamp, rather than insecure NTP. For a small fee, NRC offers Authenticated NTP Services.

For a complete explanation of Network Time Protocol and the latest information on NTP, visit the NTP source.

To make use of NTP service and have your computer's clock set to NRC time, you will need software that can request time over the Internet.

A version of the NTP client software used to synchronize computer clocks is called Simple Network Time Protocol (SNTP). The software for various computers can be downloaded from many sites on the Internet. Here is a brief list of some sites:

•  Time Synchronization Software
•  Des Logiciels Clients NTP
•  Yahoo Time Page

Install the software as indicated. To configure it to synchronize your clock to NRC time, you must set the NTP server to the following host name (do not use the IP address, as this may change):

time.nrc.ca

time.chu.nrc.ca

This second time server is located at a different site on a different network than the first time server. Both servers are controlled in the same way by atomic clocks operated by NRC and provide official time with the same accuracy. The maintainance of seperate servers will offer redundancy and a more reliable time service to Canadians in case of network outage and other difficulties.

For users who have an NTP server on their system and would like to synchronize to NRC time, configure your daemon to include the above NTP server address. This is a stratum-2 server. For users who require service from a stratum-1 server, contact NRC for the address of these servers.

For users who would like to set up NTP service in their organization, but do not have access to a stable clock source, you can do so by taking advantage of atomic clocks at time labs around the world, such as NRC. Distribution software for NTP is available from the NTP source, free of charge for various types of computers. You will not need a "radio clock" if you are operating a secondary (stratum-2 or higher) server. Simply configure your NTP server to synchronize to lower stratum servers. Filter algorithms in the NTP protocol can provide a very stable clock on your network server, despite Internet time noise.

Note: Not all computer synchronization software use the NTP protocol. Some use older time protocols that can not offer accurate time when used over the Internet. NRC no longer supports these older protocols (TIME, port 37 and DAYTIME, port 13), on the host mentioned above. For the most accurate time transfer, ensure your clock synchronization software is configured to use the NTP or SNTP protocols.

Technical Notes

NRC's Network Time Protocol complies with version 4 specification as outlined in RFC-1305. The servers also support the Simple Network Time Protocol (SNTP) which complies with version 4 specifications as outlined in RFC2030.

There are three stratum-1 server hosts at each network site. These are Pentium computers using the Linux operating system. These servers us version 4.1.0 of the NTP distribution software. An NTP host operating as a primary or stratum-1 time server is directly synchronized to a source of accurate time. At the NRC main lab, the three stratum-1 servers are connected to Leitch 5300 Master Clock drivers which are synchronized to three separate cesium atomic frequency standards. The secondary site is at radio station CHU. Here the reference clocks are the code generators that create the Broadcast Code used by the shortwave transmitters. The code generators are synchronized to atomic clocks.

NRC also operates stratum-2 servers. A stratum-2 server can also disseminate NTP time. Our stratum-2 servers are Pentium PCs with the Linux operating system. These servers use version 4.1.1 of the NTP distribution software. They will get their time from the three stratum-1 servers. For all practical purposes, the average time disseminated by the stratum-2 server is the same as the stratum-1 servers.

The stratum-2 service is provided at the following host names:

time.nrc.ca

time.chu.nrc.ca

The service at time.nrc.ca is actually served by two servers at different IP addresses. The DNS server will resolve the lookup to either server. Do not use the IP address, as this may change. Both servers provide official time for Canada with the same accuracy.

Contact NRC if you require service from our stratum-1 servers.

A note of warning to users who are trying to synchronize a computer protected by a firewall; make sure your firewall allows incoming NTP packets from our servers to your computer. If not, you will not be able to synchronize your computer to our time service.

Further Information

Raymond Pelletier
phone: (613) 993-3430
fax: (613) 952-1394
email:time@nrc-cnrc.gc.ca