Hirschmann RS20 User Manual page 150

Synchronizing the system time in the
Reference
(Master clock)
PTP
UDP
Delay + Jitter
IP
MAC
Phy
PTP Precision Time Protocol (Application Layer)
UDP User Datagramm Protocol (Transport Layer)
IP Internet Protocol (Network Layer)
MAC Media Access Control
Phy Physical Layer
Figure 46: 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
devices 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
calculations.
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).
150
Delay + Jitter
Delay + Jitter
LAN
8.3 Precision Time Protocol
Local
(Slave clock)
PTP
UDP
IP
MAC
Phy
Basic Configuration L2P
Release 4.2 07/08