3Com SUPERSTACK 3 WEBCACHE 3000 User Manual page 133

Network Time Protocol 133
Choosing a Network You can choose to use one of the many public NTP servers that are
Time Protocol Server available on the Internet or set up your own NTP server. When you have
access to an NTP server, you can configure the Webcache to determine
the current time using NTP; see "Configuring the System Time Using the
Network Time Protocol" on page 134 for further information.
Public NTP servers are grouped into stratums. The NTP primary (stratum 1)
servers are connected to a reference clock, which is typically an expensive
cesium clock or cheaper GPS receiver. Servers operating at stratum 1 are
the most accurate available, but also the fewest in number because of
the prohibitive cost of reference clocks.
The NTP secondary (stratum 2) servers are in turn connected to a stratum
1 server and are therefore less accurate but greater in number. Stratum 3
servers are connected to stratum 2 servers, and so on, up to an imposed
limit of 15 strata. You should not use a high level public stratum server
because of their limited number and because the load placed on them is
increasingly heavy.
For a list of well known NTP servers available for public use, view the
Microsoft Knowledge Base at:
http://search.support.microsoft.com/kb/c.asp
(correct at time of publishing)
and search for the article ID number , or enter the following URL
Q262680
in your Web browser:
http://www.eecis.udel.edu/~mills/ntp/servers.htm
(correct at time of publishing)
3Com recommends that if your network has an internal NTP server, you
should use this rather than a public stratum server. If not, you should use
the lowest stratum public NTP server available to you.