Hirschmann MACH 4000 Series, User Manual

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Synchronizing the System Time of the
Basic - L3P
Release 3.1 06/07
7.3 Precison Time Protocol
111
7.3 Precison Time Protocol
7.3.1 Funtion description PTP
The requirment for running time-critical applications over a LAN is a precise
time management system. The IEEE 1588 standard with the Precision Time
Protocol (PTP) describes a procedure that is based on the principle that one
clock is the most precise and makes it possible to synchronize all clocks
within a LAN.
This procedure permits synchronization of the clocks with a level of accuracy
in the hundreds of nanoseconds. The synchronization messages have
virtually no effect on the network load. PTP uses multicast communication.
Factors influencing precision are:
D
Accuracy of the reference clock
IEEE 1588 classifies clocks according to their accuracy. An algorithm that
measures the accuracy of the available clocks in the network determines
the most accurate time for the “grandmaster” clock.
Stratum number Specification
0
For temporary, special purposes to assign one clock a better value than all
lother clocks within the network.
1 Designates the clock with the highest precision as the reference clock. A
stratum 1 clock can be both a boundary and an ordinary clock. Stratum 1
clocks include GPS clocks and calibrated atomic clocks. A stratum 1 clock
cannot be synchronized via PTP from another clock in the PTP system.
2 Designates the clock as the second-choice reference clock and cannot be
synchronized via PTP from another clock in the PTP system.
3 Designates the clock that can synchronize other devices via an external
cable as the reference clock.
4 Designates the clock as the reference clock.
5–254 Reserved.
255 Default setting. Such a clock should never be the best master clock.
Table 6: Stratum – Classifying the clocks