Using i!-Schedule
8
i!-Schedule
Time Protocols
i!-Schedule supports four time protocols to synchronize the NetLinx Master’s clock with and
Internet timeserver:
DayTime (13/udp, 13/tcp)
Time (37/udp, 37/tcp)
SNTP (123/udp)
SNTP Broadcast (123/udp).
Only one of the protocols can be active at a time.
The DayTime protocol is based on RFC 867 and can provide Day and Time information. While the
Daytime protocol can provide accurate day and time formation, RFC867 does not specify the actual
format for the message. This limits the usefulness of the DayTime protocol with one exception: The
National Institute of Standards and Technology operate a series of Time Servers, known as the
NIST Internet Time Servers, that provide a DayTime message of fixed format than can be reliably
parsed and can be used to accurately set the Day and Time of any clock. While these Time Servers
reside in the US, the Day and Time of the servers is supplied in Universal time Coordinates or
UTC. The Time Management portion of i!-Schedule is capable of connecting to any of the NIST
Time servers and calculating the correct time and date for any location in the world. The Time
Manager also supports the standard NIST server list, a file called nist-srv.lst, and will attempt to
read this file from doc:\user\time. You may get a copy of this file from the /pub directory on any
NIST timeserver. If this file cannot be found on the NetLinx file system, a default list of NIST
servers will be used instead. See the NIST home page at
http://www.boulder.nist.gov/timefreq/
index.html
for more information on NIST Time service or Servers.
Additionally, the Time Manager in i!-Schedule has also been written to use a "popular" DayTime
format which is used by the Linux implementation of DayTime and Tardis, a popular time synching
software. Although not specified, the Date and Time of this format does not specify the time zone
and is assumed to be local. If you select DayTime protocol and select a server that is running
DayTime and the format, specifically "DayOfWeek Month Day HH:MM:SS Year", can be found,
no time offset will be added. If you have chosen this combination and find that the time does not
synchronize to the correct time, choose another protocol or server.
The Time protocol, based on RFC868, is a very simple straightforward time protocol providing the
number of seconds that have transpired since January 1, 1900 UTC. The current Date and time can
easily be calculated form this value. However, the number of seconds in this protocol is provides as
a 32 bit unsigned number, which can represent a maximum value of 4294967295 (2 ^ 32).
4294967295 seconds from January 1st, 1900 occurs on Feb 7, 2036 at 6h 28m 16s. Therefore, this
protocol can only accurately represent time before this date. Many of the NIST servers, as well and
many Unix, Linux and Windows programs, can provide this time protocol, and it can be reliably
used up until Feb 7, 2036.
The last two Time protocols share the same message format but differ in their connection scheme.
SNTP stands for Simple Network Time Protocol, a subset of NTP or Network Time Protocol, is
based on RFC2030. It is a highly accurate measure of time and date and also measures Date and
Time as the number of seconds from January 1st 1900. However, the number of seconds is provided
in two parts: the number of whole seconds, with a range of 4294967295 (2^32) and fractions of a
second also with a range of 4294967295 (2^32). The Netlinx master is not able to take advantage of
