| Network Time Protocol seems to have been | | | | transmissions or via the GPS (Global Positioning |
| around for ever. In fact it is indeed one of the | | | | System) network. |
| Internet’s oldest protocols having been | | | | The NTP algorithm uses this time reference to |
| developed in the 1980’s by Professor David | | | | determine the amount to advance or retreat the |
| Mills and his team from Delaware University. | | | | system or network clock. NTP analyses the |
| In a laid-back world it perhaps doesn’t matter | | | | timestamp’s values including the frequency of |
| if computer networks are not synchronised. The | | | | errors and its stability. A NTP server will maintain |
| only consequences of timing errors could be that | | | | an estimate the quality of both the reference |
| an email arrives before it was sent but in | | | | clocks and itself. |
| industries such as airline seat reservation, the | | | | NTP is hierarchical. The distance from the timing |
| stock exchange or satellite communication, | | | | reference is divided into strata. Stratum 0 is the |
| fractions of a second can cause serious errors | | | | atomic clock reference; Stratum 1 is the NTP |
| such as selling seats more than once, the loss of | | | | server, while Stratum 2 is a server that receives |
| millions of dollars or even fraud. | | | | timing information from the NTP server. NTP can |
| Computers are logical machines and as time is | | | | support almost limitless strata although the further |
| linear to a computer any event that happens on | | | | away from the timing reference you go the less |
| one machine must happen before news of that | | | | accurate it will be. |
| event reaches another. When networks are not | | | | As each stratum level can both receive and send |
| synchronised computers struggle to deal with | | | | timing signals, the advantage of this hierarchical |
| events that have obviously occurred (such as an | | | | system is that thousands of machines can be |
| email being sent) but according to their clock and | | | | synchronised with only the need for one NTP |
| time stamp it hasn’t yet, just think back to | | | | server. |
| the millennium bug where it was feared clocks | | | | NTP contains its a security measure called |
| would jump back to 1900! | | | | authentication. Authentication verifies that each |
| For this very reason NTP was developed. NTP | | | | timestamp has come from the intended time |
| uses an algorithm (Marzullo’s algorithm) to | | | | reference by analysing a set of encryption keys |
| synchronise the time with the current version of | | | | that are sent with the time reference. NTP |
| NTP can maintain time over the public Internet to | | | | analyses it and confirms whether it has come |
| within 10 milliseconds and can perform even | | | | from the time source by verifying it against a set |
| better over LANs. NTP time servers work within | | | | of trusted keys in its configuration files. |
| the TCP/IP suite and rely on UDP (User Datagram | | | | However, authentication is unavailable from timing |
| Protocol). | | | | sources from across the Internet which is why |
| NTP servers are normally dedicated NTP devices | | | | Microsoft and Novell amongst others strongly |
| that use a single time reference to synchronise a | | | | recommend only external time references are |
| network to. This time reference is most often a | | | | used such as a dedicated GPS NTP server or one |
| UTC (Coordinated Universal Time) source. UTC is | | | | that receives the national time and frequency long |
| a global time scale distributed by atomic clocks via | | | | wave transmission. |
| the Internet, specialist long wave radio | | | | |