The Network Time Protocol (NTP) is the mechanism widely used on the Internet to distribute very accurate time information which can then be used by systems on the Internet to set their clocks. NTP regards the involved systems as having a "stratum". A stratum 1 system has a directly attached accurate time piece such as a radio clock or an atomic clock. A stratum 2 system is one that is currently synchronising from a stratum 1 system and so on.
JANET runs an NTP service to which the University of Cambridge subscribes, so an NTP service is available to University Departments, Colleges and Institutions on an experimental basis. Formally, no promises or guarantees of any sort are offered, but it is is expected that the service will continue.
The University is allowed only a small number of links to the national servers, and those only under the auspices of the UIS, the intent being that the UIS should further distribute time within the University. Such indirection is necessary to avoid the national servers becoming overloaded to the detriment of accuracy. The UIS servers are stratum 2 servers.
Similarly, the UIS expects its stratum 2 servers to serve departmental (or comparable) stratum 3 servers rather than individual end systems. These stratum3 systems are then expected to supply time information to the other machines in the department concerned. Providing such a departmental service is no big deal, requiring only a very small part of some stable Unix machine to run a freely available daemon that consumes few resources and normally requires no attention after setting up. In point of fact the same software is used on Unix systems in servers and in end systems; it is merely a detail of the configuration file. Information is available on setting up a stratum 3 server.
Limited support is available for systems that do not have a departmental stratum 3 service. UIS has a small number of stratum 3 servers which it is prepared to make available for direct use. This is considerably less desirable to all concerned than the mechanisms described above. Information is available on directly attaching stratum 4 clients.
- The NTP Home Page
This is the main home page for NTP on the Internet, maintained partly by Dave Mills, the creator of the protocol.
- Setting up a stratum 3 server
This page covers the servers to use to set up one or more departmental stratum 3 servers.
- Setting up a stratum 4 client
This page describes what stratum 3 servers to use if there is no stratum 3 service local to your machine.