Network Time Protocol NTP Speaker Chenglin Tsai NTP

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Network Time Protocol NTP Speaker: Cheng-lin Tsai

Network Time Protocol NTP Speaker: Cheng-lin Tsai

NTP - Introduction ü NTP is a protocol for synchronizing the clocks on computers

NTP - Introduction ü NTP is a protocol for synchronizing the clocks on computers over packet-switched data networks ü NTP delivers accurate and reliable time in spite of faults in the network ü Provides a connectionless service (UDP in the Transport Layer) ü NTP is used on Internet

NTP - Clock Strata ü NTP uses a hierarchical organization of clocks • Stratum

NTP - Clock Strata ü NTP uses a hierarchical organization of clocks • Stratum 0. - Composed by: Atomic Clocks, GPS Clocks. • Stratum 1 - Primary Time Servers. - Computers attached to stratus 0 devices • They act as servers for requests from Stratus 2 • • Stratum 2 Computers sending NTP requests to Time Servers in Stratum 1 • Computers in this level will reference to several time servers to synchronize their clocks • S 2 Computers will peer with another S 2 computers to provide more reliable and robust time for all devices in the peer group • They act as servers for requests from Stratus 3 •

NTP - Clock Strata • Stratum 3, 4, … Computers employ the same NTP

NTP - Clock Strata • Stratum 3, 4, … Computers employ the same NTP function as in Stratum 2 • Potentially up to 16 levels • * Image taken from www. wikipedia. com

NTP - Synchronization Subnet ü Computer local clock are synchronized to a number of

NTP - Synchronization Subnet ü Computer local clock are synchronized to a number of Time Servers and peer computer ü The set of these computers and Time Servers is known as the Synchronization Subnet ü The Stratum Number for each computer is determined by the hop count to the root (Strata 0)

NTP - Synchronization Subnet ü Example:

NTP - Synchronization Subnet ü Example:

NTP - Determining Time ü Timestamps exchanged between the server and clients (subnet peers)

NTP - Determining Time ü Timestamps exchanged between the server and clients (subnet peers)

NTP - Determining Time ü Examples:

NTP - Determining Time ü Examples:

Demo } Free. BSD § ntp-4. 2. 4 p 7. tar. gz

Demo } Free. BSD § ntp-4. 2. 4 p 7. tar. gz

NTP - References [ 1 ] D. Mills, “Internet Time Synchronization: The Network Time

NTP - References [ 1 ] D. Mills, “Internet Time Synchronization: The Network Time Protocol”, IEEE Trans. on Communications, vol. 39, no. 10, pp. 1482 – 1493, Oct. 1991. ü [ 2 ] NTP: The Network Time Protocol - www. ntp. org ü [ 3 ] Wikipedia - www. wikipedia. com ü

NTP - References Questions ?

NTP - References Questions ?