Introduction to NTP (Network Time Protocol), NTP Stratum Levels

Network Time Protocol (NTP, defined in RFC 1305, RFC 5905) is a protocol which is used widely in networking industry to synchronize the clocks of network infrastructure devices (Servers, Routers, Switches, Computers) over a network. Network Time Protocol (NTP) allows network infrastructure device to keep its system time synchronized to an external accurate time source. Time accuracies of range 1 to 50 ms is possible with NTP based on different network conditions.

Please visit official Network Time Protocol (NTP) documentation to get more knowledge about Network Time Protocol (NTP).

In Network Time Protocol (NTP), time is distributed from a high precision time device in an hierarchical way, with the primary servers at the top keeping the master time, and distributing the time down to the secondary servers and so forth. In Network Time Protocol (NTP), Stratum levels define the distance from a high precision Reference Clock. A Stratum-0 device is assumed to be most accurate and it has no delay. Each server participating in the hierarchy are allocated a stratum, with Stratum-1 being the master servers (which are connected to High Precision time source), Stratum-2 the secondary servers, down to the lower end of Stratum-15.

Stratum-0 consists of high precision time sources. Stratum-0 Time Devices are very accurate reference clocks (Example: Atomic Clocks). Stratum-0 time devices cannot be used on the network directly as an NTP Server. Stratum-0 time devices are connected to Stratum-1 Time Servers. That is, Stratum-1 Time Servers get their time synchronized from a Stratum-0 time source. Stratum-1 Servers are also referred to as primary NTP time servers.

An NTP server that is directly connected to a Stratum-0 device is called a Stratum-1 Time Server. An NTP Server, which is getting its time synchronized from a Stratum-1 time server is called as Stratum-2 NTP time server. Stratum-2 Time Servers get their time synchronized from a Stratum-1 time source. A Server, which is getting its time synchronized from a Stratum-2 time server is called as Stratum-3 time server and so on. Stratum-3 Time Servers get their time synchronized from a Stratum-2 time source.

In NTP hierarchy, Stratum-0 level device has the most precise time, Since Stratum-1 NTP Server is synchronizing its time from Stratum-0 time device, Stratum-1 is less precise than Stratum-0 and so on.

NTP Stratum levels up to 15 are valid Stratum Levels. In Network Time Protocol (NTP), Stratum-16 is used to indicate that a device time is not synchronized.