Hirschmann MACH 4000 Series, User Manual

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Synchronizing the System Time of the
112
7.3 Precison Time Protocol
Basic - L3P
Release 3.1 06/07
D
Cable delays; device delays
The communication protocol defined by IEEE 1588 makes it possible to
measure cable delays. Formulas for calculating the current time eliminate
delays.
D
Accuracy of local clocks
The communication protocol defined by IEEE 1588 takes into account the
inaccuracy of local clocks in relationship to the reference clock.
Calculation formulas permit the synchronization of the local time, taking
the inaccuracy of the local clock into consideration in relationship to the
reference clock.
Fig. 28: Delay and jitter problems when synchronizing clocks
To get around the delay and jitter in the protocol stack, IEEE 1588 recom-
mends inserting a special hardware time stamp unit between the MAC and
the PHY layer. Devices or modules with the name supplement “RT” are
equipped with this time stamp unit.
The delay and jitter in the LAN increase in the media and transmission
devices along the transmission path.
PTP
Reference
(Master clock)
UDP
IP
MAC
Phy
PTP
UDP
IP
MAC
Phy
Local
(Slave clock)
LAN
PTP Precision Time Protocol (Application Layer)
UDP User Datagramm Protocol (Transport Layer)
IP
Internet Protocol (Network Layer)
MAC Media Access Control
Phy Physical Layer
Delay + Jitter
Delay + Jitter Delay + Jitter