Time Protocol
Network Working Group
J. Postel - ISI
Request for Comments: 868 K. Harrenstien
- SRI May 1983
This
RFC specifies a standard for the ARPA Internet community.
Hosts on the ARPA Internet that choose to implement a Time Protocol
are expected to adopt and implement this standard.
This
protocol provides a site-independent machine-readable date and time.
The Time service sends back to the originating source the time
in seconds since midnight on January first 1900.
One
motivation arises from the fact that not all systems have a date/time
clock, and all are subject to occasional human or machine error. The
use of time-servers makes it possible to quickly confirm or correct a
system’s idea of the time, by making a brief poll of several independent
sites on the network.
This
protocol may be used either above the Transmission Control Protocol (TCP)
or above the User Datagram Protocol (UDP).
When
used via TCP, the time service works as follows:
S: Listen on port 37 (45 octal).
U: Connect to port 37.
S: Send the time as a 32 bit binary number.
U: Receive the time.
U: Close the connection.
S: Close the connection.
The
server listens for a connection on port 37. When
the connection is established, the server returns a 32-bit time value
and closes the connection. If the server is unable
to determine the time at its site, it should either refuse the connection
or close it without sending anything.
When
used via UDP, the time service works as follows:
S: Listen on port 37 (45 octal).
U: Send an empty datagram to port 37.
S: Receive the empty datagram.
S: Send a datagram containing the time as
a 32 bit binary number.
U: Receive the time datagram.
The
server listens for a datagram on port 37. When a
datagram arrives, the server returns a datagram containing the 32-bit
time value. If the server is unable to determine
the time at its site, it should discard the arriving datagram and make
no reply.
The
time is the number of seconds since 00:00 (midnight) 1 January 1900 GMT,
such that the time 1 is 12:00:01 am on 1 January 1900 GMT; this base will
serve until the year 2036.
For
example, the time:
2,208,988,800
corresponds to 00:00 1 Jan 1970 GMT,
2,398,291,200
corresponds to 00:00 1 Jan 1976 GMT,
2,524,521,600
corresponds to 00:00 1 Jan 1980 GMT,
2,629,584,000
corresponds to 00:00 1 May 1983 GMT, and
-1,297,728,000
corresponds to 00:00 17 Nov 1858 GMT.
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