3com Webcache 1000 (3C16115) Benutzerhandbuch

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The Network Time Protocol (NTP) is used to synchronize the time of client 
machines and servers with other well-known, highly accurate servers or 
reference time sources. It maintains a consistent Coordinated Universal 
Time (UTC) within your network which is far more accurate than the 
internal system clocks of client machines and prevents time drift from 
occurring on the Webcache.

NTP provides client machine and server time accuracies typically within a 
millisecond on LANs, relative to a primary NTP server synchronized to UTC 
via a Global Positioning Service (GPS) receiver. Such accurate 
time-keeping is an essential part of the operation of the Webcache.

You can choose to use one of the many public NTP servers that are 
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 69 for more 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.