1. Network Time Protocol - NTP Speaker: Cheng-lin Tsai

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

3. NTP - Clock Strata NTP uses a hierarchical organization of clocks NTP uses a hierarchical organization of clocks Stratum 0.- Composed by: Atomic Clocks, GPS Clocks. Stratum 0.- Composed by: Atomic Clocks, GPS Clocks. Stratum 1 - Primary Stratum 1 - Primary Time Servers.- Computers attached to stratus 0 devices Time Servers.- Computers attached to stratus 0 devices They act as servers for requests from Stratus 2 They act as servers for requests from Stratus 2 Stratum 2 Stratum 2 Computers sending NTP requests to Time Servers in Stratum 1 Computers sending NTP requests to Time Servers in Stratum 1 Computers in this level will reference to several time servers to synchronize their clocks Computers in this level will reference to several time servers to synchronize their clocks S2 Computers will peer with another S2 computers to provide more reliable and robust time for all devices in the peer group S2 Computers will peer with another S2 computers to provide more reliable and robust time for all devices in the peer group They act as servers for requests from Stratus 3 They act as servers for requests from Stratus 3

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

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

6. NTP - Synchronization Subnet Example: Example:

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

8. NTP - Determining Time Examples: Examples:

9. Demo  FreeBSD  ntp-4.2.4p7.tar.gz

10. 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. [ 2 ] NTP: The Network Time Protocol - www.ntp.orgwww.ntp.org [ 3 ] Wikipedia - www.wikipedia.comwww.wikipedia.com

11. NTP - References Questions ?