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NTP servers obtain accurate time from an external timing reference, such as GPS or Radio time and frequency transmissions. A NTP Server provides networked clients primarily with three peices of information: system clock offset, network delay and dispersion relative to an external reference clock. The Network Time Protocol is structured in a heirachical configuration; primary servers, secondary servers and time clients. Primary NTP servers are synchronised to an accurate external clock and is attributed a stratum, or hierarchy, level of one. Secondary NTP servers synchronise to primary servers and provide a buffer between primary servers and clients. Secondary servers are attributed a stratum of greater than one. As the stratum increases, so the accuracy of the server decreases. The Network Time Protocol uses the TCP\IP UDP protocol (User Data-gram Protocol). NTP protocol messages consist of a number of distinct fields: Leap Indicator; Version Number; Mode; Stratum; Poll; Precision; Root Delay; Root Dispersion; Reference Identifier; Reference Timestamp; Originate Timestamp; Receive Timestamp; Transmit Timestamp; Key Identifier and Message Digest. A NTP server can operate in three modes: unicast; anycast and multicast. In unicast and anycast modes, the client transmits a NTP request message to the server. The server responds with a NTP time message that the client uses for time synchronisation. In multicast mode, NTP time messages are broadcast at periodic specified intervals. The current release of NTP is version 4. The only significant modification to the protocol between versions 3 and 4 is a slight header re-interpretation to accommodate IPv6. All versions of NTP are backwards compatible and can be freely interchanged. SNTP, or Simple Network Time Protocol, is a simplification of the full-blown Network Time Protocol. It can be used where the complexities of the full-blown protocol are not required. SNTP is often implemented on Microsoft Windows platforms where many of the complex algorithms for maintaining accurate time are unavailable. SNTP can be implemented when the high synchronisation performance of NTP is not required. The message format of the SNTP protocol is almost identical to that of the NTP protocol. However, the complex subroutines designed to maintain a highly accurate synchronised time are removed or simplified. Small computers with reduced processing power, such as micro-controllers or monitoring equipment most often use SNTP. The NTP and SNTP protocols are interoperable and can be interchanged without problem. Article Source: http://www.articlewheel.com
David Evans is a technical author in the field of computer time synchronisation and telecommunications. Click here if you would like more information on NTP server systems.
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