User manual

Publication 1783-UM003D-EN-E - December 2009 83
Chapter 3
Synchronize the Switch
with Other Devices via PTP
The IEEE 1588 standard defines a protocol, called Precision Time Protocol,
or PTP, which enables precise synchronization of clocks in measurement and
control systems. The clocks communicate with each other over the
EtherNet/IP communication network. The PTP protocol enables
heterogeneous systems that include clocks of various inherent precision,
resolution and stability to synchronize. PTP generates a Master-Slave
relationship among the clocks in the system. All clocks ultimately derive their
time from a clock selected as the grandmaster clock.
By default, PTP is enabled on all the Fast Ethernet and Gigabit Ethernet ports
on the base switch module. Only the ports on the base switch module are
PTP-capable. The switch expansion modules do not support PTP.
The switch supports two synchronization clock modes:
• End-to-End Transparent mode The switch transparently
synchronizes all slave clocks with the master clock connected to the
switch. This is the default mode.
The switch corrects the delay incurred by every packet passing through
the switch (referred to as residence time). This mode causes less jitter
and error accumulation than boundary mode.
In End-to-End Transparent mode, all switch ports in the base are
enabled.
• Boundary mode The switch becomes the parent clock to which the
other devices connected to the switch synchronize their internal clocks.
The switch and connected devices constantly exchange timing messages
to correct time skew caused by clock offsets and network delays.
This mode can eliminate the effects of latency fluctuations. Because
jitter and errors can accumulate in cascaded topologies, this mode
should be used only for networks with less than 4 layers of cascaded
devices.
In Boundary mode, one or more switch ports can be PTP-enabled.
IMPORTANT
Do not connect PTP-capable devices to expansion ports. All PTP
packets received by a non-PTP-capable port on a switch
supporting PTP are discarded.