Synchronizing the system time in the
12
7.3
Precision Time Protocol
Basic - L3P
Release
4.0
11/07
Figure 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
Phy layers. Devices/modules with the "-RT" suffix in their names are
equipped with this time stamp unit.
The delay and jitter in the LAN increase in the media and transmission devic-
es along the transmission path.
The cable delays are relatively constant. Changes occur very slowly. IEEE
1588 takes this fact into account by regularly making measurements and cal-
culations.
IEEE 1588 eliminates the inaccuracy caused by delays and jitter by defining
boundary clocks. Boundary clocks are clocks integrated into devices. These
clocks are synchronized on the one side of the signal path, and on the other
side of the signal path they are used to synchronize the subsequent clocks
(ordinary clocks).
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
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