NTP protocol full name of the Network Time Protocol (Network Time Procotol). Its purpose is to deliver a unified, standard time on the Internet. Specific implementation is specified on the number of clock source network site to provide users with timing services, and between these sites should be able to compare with each other, improve accuracy.
NTP was first used by Professor Mills Delaware University in the United States designed to achieve, from 1982 to now has been developed originally proposed nearly 20 years, in 2001 the latest NTPv4 accuracy has reached 200 milliseconds. For practical applications, but also to ensure the accuracy of the second stage the SNTP (Simple Network Time Protocol). This project uses the online time transfer format NTPv3 published in 1992, almost all of the current timing of the site are based on NTPv3. (Later will detail the basic principles of NTPv3, architecture and operating mode.)
TCP / IP is a protocol suite including the TCP , the IP, the UDP, the ICMP, the RIP, the TELNET, the FTP, the SMTP, the ARP, the TFTP protocols such. NTP protocol is the OSI reference model layer protocols, in line with UDP transport protocol format, has a dedicated port 123.
Reproduced in: https: //www.cnblogs.com/henryhappier/archive/2010/01/26/1656415.html