Network Working Group J. Postel Request for Comments: 867 ISI May 1983
One daytime service is defined as a connection based application on TCP. A server listens for TCP connections on TCP port 13. Once a connection is established the current date and time is sent out the connection as a ascii character string (and any data received is thrown away). The service closes the connection after sending the quote.
Another daytime service service is defined as a datagram based application on UDP. A server listens for UDP datagrams on UDP port 13. When a datagram is received, an answering datagram is sent containing the current date and time as a ASCII character string (the data in the received datagram is ignored).
There is no specific syntax for the daytime. It is recommended that it be limited to the ASCII printing characters, space, carriage return, and line feed. The daytime should be just one line.
One popular syntax is:
Weekday, Month Day, Year Time-Zone
Tuesday, February 22, 1982 17:37:43-PST
Another popular syntax is that used in SMTP:
dd mmm yy hh:mm:ss zzz
02 FEB 82 07:59:01 PST