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NTP (Network Time Protocol)
« on: September 09, 2007, 12:46:09 PM »
SOURCE: Wikipedia.Org

The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123 as its transport layer. It is designed particularly to resist the effects of variable latency (jitter).

NTP is one of the oldest Internet protocols still in use (since before 1985). NTP was originally designed by Dave Mills of the University of Delaware, who still maintains it, along with a team of volunteers.

NTP is not related to the much simpler DAYTIME (RFC 867) and TIME (RFC 868) protocols.

Overview

NTP uses Marzullo's algorithm with the UTC time scale, including support for features such as leap seconds. NTPv4 can usually maintain time to within 10 milliseconds (1/100 s) over the public Internet, and can achieve accuracies of 200 microseconds (1/5000 s) or better in local area networks under ideal conditions.

The NTP Unix daemon is a user-level process that runs continuously on a machine that supports NTP, and most of the protocol is implemented in this user process. To get the best performance from NTP, it is important to have the standard NTP clock phase-locked loop implemented in the operating system kernel, rather than using only the intervention of the external NTP daemon: all recent versions of the Linux and Solaris operating systems have this support.

The operational details of NTP are illustrated in RFC 778, RFC 891, RFC 956, RFC 958, and RFC 1305. The current reference implementation is version 4 (NTPv4); however, as of 2005, only versions up to 3 (1992) have been documented in RFCs. The IETF NTP Working Group has formed to standardize the work of the NTP community since RFC 1305 et al.

A less complex form of NTP that does not require storing information about previous communications is known as the Simple Network Time Protocol or SNTP. It is used in some embedded devices and in applications where high accuracy timing is not required. See RFC 1361, RFC 1769, RFC 2030 and RFC 4330.

Microsoft Windows 2000 and XP include the Windows Time Service, which has the ability to sync the computer clock to an NTP server. However, the version in Windows 2000 only implements SNTP. As of Windows Server 2003 Service Pack 1, the Windows Time Service implements the more robust NTPv3 protocol as specified in RFC 1305.

Clock strata

(Note that this is different from the notion of clock strata used in telecommunications systems.)

NTP uses a hierarchical system of "clock strata". The stratum levels define the distance from the reference clock and the associated accuracy.

Stratum 0
    These are devices such as atomic (cesium, rubidium) clocks, GPS clocks or other radio clocks. Stratum-0 devices are not attached to the network; instead they are locally connected to computers (e.g. via an RS-232 connection using a Pulse per second signal).
Stratum 1
    These are computers attached to Stratum 0 devices. Normally they act as servers for timing requests from Stratum 2 servers via NTP. These computers are also referred to as time servers. Many Stratum 1 servers (for NTP v3 and earlier versions) may not actually be operating with Stratum 1 precision. As the NTP protocol is developed, it will become less and less possible for misleading Stratum 1 servers to run -- instead the protocol would automatically bump the server Stratum level down accordingly.
Stratum 2
    These are computers that send NTP requests to Stratum 1 servers. Normally a Stratum 2 computer will reference a number of Stratum 1 servers and use the NTP algorithm to gather the best data sample, dropping any Stratum 1 servers that seem obviously wrong. Stratum 2 computers will peer with other Stratum 2 computers to provide more stable and robust time for all devices in the peer group. Stratum 2 computers normally act as servers for Stratum 3 NTP requests.
Stratum 3
    These computers employ exactly the same NTP functions of peering and data sampling as Stratum 2, and can themselves act as servers for higher strata, potentially up to 16 levels. NTP (depending on what version of NTP protocol in use) supports up to 256 strata. It is hoped that in NTP 5 (a protocol still in development) that only 8 or 16 strata will be permitted.

-------->>>>>>...

NTP is very useful to those organization nga nag-gamit ug Time Attendance System, computers/time keeping machines will sync time from the master server which is connected to the internet (accurate time is business).

For single PC nga connected directly sa internet, you can check if your running NTP by issuing this command at the command prompt:

C:\Documents and Settings\marcopolo>net time /querysntp

The current SNTP value is: time.windows.com,0x1  --> set by default on windows system

To change the server:
C:\Documents and Settings\marcopolo>net time /setsntp:SERVER_NAME

For Unix/Linux/BSD/other *nixes, it will cost you some dollars if you're going to ask me. ;D  JOKE!

just send me your questions thru PM...  ;)

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Re: NTP (Network Time Protocol)
« Reply #1 on: September 13, 2007, 04:28:54 AM »
I'm not so familiar with this NTP, galen.
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G@Len

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Re: NTP (Network Time Protocol)
« Reply #2 on: September 23, 2007, 03:22:29 PM »
hi mike, dili ni sya kaayo common pero this is implemented to some companies nga kinahanglan nga naka-sync ilang time. previously gamit namo ni sya to sync time sa philippine manufacturing plant with the rest of the MFG plants (europe, america, ug asia) then gamit sya sa time-in/time-out sa mga workers pud. ang oras nga makita sa PC ug sa time keeper machines are exactly the same (up to the sec).



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