WESM zl Management and Configuration Guide WT.01.28 and greater

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Configuring the ProCurve Wireless Edge Services zl Module
Enabling Secure Network Time Protocol (NTP)
Figure 2-88. NTP Clock Stratum Levels
The devices at stratum 0 are GPS clocks or other radio clocks. These devices are not
attached to the network but are locally connected to computers.
Computers at stratum 1 are attached to stratum 0 devices. Stratum 1 devices can act
as time servers for timing requests from stratum 2 servers via NTP.
Computers at stratum 2 send NTP requests to stratum 1 servers. Normally, a stratum2
computer will reference a number of stratum 1 servers and use the NTP algorithm to
gather the best data sample, dropping any stratum 1 servers that seem obviously
wrong. Stratum 2 computers are peers to other stratum 2 computers, providing more
stable and robust time for all devices in the peer group. Stratum 2 computers normally
act as servers for stratum 3 NTP requests.
Computers at stratum 3 and higher employ exactly the same NTP functions of peering
and data sampling as stratum 2, and can themselves act as servers for higher strata,
potentially up to 16 levels (stratum 0 through stratum 15).