Network Time Protocol or NTP is a communications protocol that is use to syncronise time across the internet and communications networks.
What is a Stratum 0 Time Server or Clock?
NTP uses a hierarchical client/server model. Each level in the hierarchy is called a stratum. At the top we have the stratum 0. This is the ultimate time reference and uses dedicated hardware devices to provide accurate time. Typically the “clock” at this stratum will be an atomic clock or a GPS satellite time signal.
What is a Stratum 1 Time Server?
At the next level in the hierarchy there are stratum 1 servers which provide time across the internet. These are clients of the stratum 0 servers. Hence the client/server model. These servers provide time across the internet and provide the most accurate timekeeping available on the internet.
What Is A Stratum?
From the above two explanations we can see that a stratum is the distance between two levels of time keeping or teo levels of accuracy. Hence the number of stratums is the distance that a particular time server is from a primary time keeping source. Stratums go from 0 to 16.
So we can see that ntp servers can reside in different stratas of the hierarchy.
Servers that are operating within the same starta can communicate with each other on a peer to peer basis (ie, we are all on the same level) and agree “who” has the most accurate time and they can then all synchronise to the most accurate time.
Another way that ntp time servers can communicate is via a broadcast (multicast) mechanism. In this case one server will broadcast a time signal and the client servers will all synchronise to that signal.
What Port does NTP Use?
Network services on a server are allocated “ports.” These are simply the address on the server where the required service is running. All major network services run on a defualt port so that it is easy to configure client computers to access the default port.
The network time protocol (ntp) uses UDP port 123 as its default port. This means that the service is available or accessable via port 123. The client computer will need to make its time synchronisation requests by connecting to this port on the ntp time server.
