3Com Webcache 1000 (3C16115) Network Time, Protocol?, Choosing a, Protocol Server, What is the

68CHAPTER 5: SYSTEM TIME

What is the	The Network Time Protocol (NTP) is used to synchronize the time of client
Network Time	machines and servers with other well-known, highly accurate servers or
Protocol?	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.
Choosing a	You can choose to use one of the many public NTP servers that are
Network Time	available on the Internet or set up your own NTP server. When you have
Protocol Server	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.

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.