Industrial Managed
Ethernet Switch – EH9711
User Manual
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137
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Figure 2.112 Webpage to Detailed Configure Mirroring for Session ID
2.16
PTP
Precision Time Protocol (PTP) is defined in IEEE 1588 as Precision Clock Synchronization for Networked Measurements and
Control Systems, and was developed to synchronize the clocks in packet-based networks that include distributed device clocks
of varying precision and stability. PTP, which is a high-precision time protocol, can be used with measurement and control
systems in local area network that require precise time synchronization. PTP is designed specifically for industrial, networked
measurement and control systems, and is optimal for use in distributed systems because it requires minimal bandwidth and
little processing overhead.
Smart grid power automation applications such as peak-hour billing, virtual power generators, and outage monitoring and
management, require extremely precise time accuracy and stability. Timing precision improves network monitoring accuracy
and troubleshooting ability.
In addition to providing time accuracy and synchronization, the PTP message-based protocol can be implemented on packet-
based networks, such as Ethernet networks. The benefits of using PTP in an Ethernet network include:
Low cost and easy setup in existing Ethernet networks
Limited bandwidth is required for PTP data packets
In an Ethernet network, switches provide a full-duplex communication path between network devices. Switches send data
packets to packet destinations using address information contained in the packets. When the switch attempts to send multiple
packets simultaneously, some of the packets are buffered by the switch so that they are not lost before they are sent. When the
buffer is full, the switch delays sending packets. This delay can cause device clocks on the network to lose synchronization
with one another.
Additional delays can occur when packets entering a switch are stored in local memory while the switch searches the MAC
address table to verify packet CRC fields. This process causes variations in packet forwarding time latency, and these variations
can result in asymmetrical packet delay times.
Adding PTP to a network can compensate for these latency and delay problems by correctly adjusting device clocks so that
they stay synchronized with one another. PTP enables network switches to function as PTP devices, including boundary clocks
(BCs) and transparent clocks (TCs).
To ensure clock synchronization, PTP requires an accurate measurement of the communication path delay between the time
source or
primary clock
and the client clock. The system clocks can be categorized based on the role of the node in the network.
