Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 352 of 669
PTP Clock Configuration
You can configure S4224 PTP clocking from the
Configuration
>
PTP
menu path. The Precision Time
Protocol (PTP) is a network protocol for synchronizing computer systems’ clocks.
Precise time information is especially important for distributed systems in automation technology. With
PTP as described in IEEE 1588, it is possible to synchronize distributed clocks to an accuracy of less
than 1 microsecond on Ethernet networks. The demands on the local clocks and the network and
computing capacity are relatively low.
Two effects are evident when setting or synchronizing clocks: 1) independent clocks initially run at an
“offset”. To synchronize them, the less accurate clock is set to the more accurate one (offset correction).
2) real clocks do not run at exactly the same speed. Therefore, the speed of the less accurate clock has
to be regulated constantly (drift correction).
PTP knows various types of clocks, and acts as a master-to-slave protocol. A clock in an end device is
known as an “Ordinary” clock, and a clock in a transmission component like an Ethernet switch is a
“Boundary” clock (BC) or “Transparent” clock (TC). A “Master” synchronizes the respective slaves
connected to it.
The synchronization process is divided into two phases. First the time difference between the master and
the slave is corrected; this is the offset correction. With IEEE1588-2008, two modes are known for the
synchronization process: two-step-mode and one-step-mode. The second phase of the synchronization,
delay measurement, determines the run time between slave and master. It is determined by the “Delay
Request” and “Delay Response” messages in a similar way, and the clocks adjusted accordingly. This
can also be done in one-step or in two-step mode. Boundary clocks are required wherever there is a
change of the communication technology or other network elements block the propagation of the PTP
messages. The IEEE1588-2008 standard knows two types of transparent clocks: End-to-End (E2E) and
Peer-to-Peer (P2P). See the IEEE Standards web site at
http://ieeexplore.ieee.org/xpl/standards.jsp
current editions and amendments.
This page lets you view current PTP clock settings and configure new settings. The default PTP page is
shown below. By default, Clock Instance 0 is present. You can configure it separately or along with other
PTP clock instances (up to four instances maximum). The default Configuration >
PTP
page:
