Meinberg LANTIME, Operating Instructions Manual, Page: 15 / 153

Why to use a Network Timeserver
A network timeserver should be used if accurate time is essential for undisturbed
operation. It is possible to synchronize computers in a network using Public Domain
Time servers over the Internet, but there are good reasons not to use them:
- The possibility to send notification via e-mail or SNMP-Trap to an administrator
in the event of any synchronisation failure.
- The computers in the network do not have a reliable internet connection.
- The computers in the network cannot rely on the availability of external timeserv-
ers. Most operators of these timeservers do not guarantee continuous availabil-
ity nor the accuracy of their service.
- NTP is able to compensate for the propagation delay of the network packets only
in case of “usual” internet traffic. However, if unforeseen occurrences cause
badly fluctuating propagation times, it is possible that the time synchronisation
is disturbed. Reasons for this may be: hacker attacks, numerous upcoming new
viruses etc.
- An own timeserver cannot be easily compromised by external sources.
Network Time Protocol (NTP)
NTP is a common method for synchronization of hardware clocks in local und
global networks. The basic concept, version 1 [Mills88], was published in 1988 as
RFC (Request For Comments). Experiences made from the practical use in Internet
was followed by version 2 [Mills89]. The software package NTP is an
implementation of the actual version 3 [Mills90], based on the specification RFC-
1305 from1990 (directory doc/NOTES). Permission to use, copy, modify and
distribute this software for any purpose and without fee is hereby granted (read File
COPYRIGHT).
NTP's way of operation is basically different from that of most other protocols. NTP
does not synchronize all connected clocks, it forms a hierarchy of timeservers and
clients. A level in this hierarchy is called a
stratum , and Stratum-1 is the highest level.
Timeservers of this level synchronize themselves by a reference time source, such as
a radio controlled clock, GPS-receiver or modem time distribution. Stratum-1-Servers
distribute their time to several clients in the network which are called Stratum-2.
A high precision synchronization is feasible because of the several time references.
Every computer synchronizes itself by up to three valued time sources. NTP enables
the comparison of the hardware times and the adjustment of the own clock. A time
precision of 128 ms, often better than 50 ms, is possible.
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