Profinet Communication - Omron CJ1W-PNT21 Operation Manual

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PROFINET Communication

PROFINET uses Ethernet and TCP, UDP and IP as basis for the communication between the devices.
TCP/IP and UDP/IP
For non-time critical messaging PROFINET uses standard Ethernet mechanisms over TCP/IP and UDP/IP.
Field devices are addressed using a MAC and IP address. This is similar to the standard Ethernet
communication. In these protocols, the networks are identified based on the IP address. Within a single network
the MAC address is used for the addressing of the target devices.
This addressing features enables integration with the IT world without limitation. The OMRON I/O Devices can
accordingly support the OMRON Ethernet protocols, enabling additional communication with OMRON
PROFINET devices.
TCP provides an error-free transmission of data from sender to receiver. It establishes a connection between
the two stations before the transmission is complete. This connection is monitored during operation and
disconnected after the transmission is complete.
UDP does not guarantee an error-free transmission of data. However, the UDP is connectionless. Each
message is an individual transmission. Because of the lack of overhead (connection establishment, monitoring,
etc.), this protocol is more suitable for time-critical applications.
RT and IRT
The TCP/IP and UDP/IP communication protocols apply a considerable amount of control overhead which will
slow down data transmission speed which is required for PROFINET applications. To facilitate Real-Time
capabilities for data exchange, the PROFINET uses a specific protocol of Real-Time (RT) Communication. This
protocol cancels some of the flow control and addressing in comparison with the TCP/IP and UDP/IP.
For the prioritized transmission of RT-frames, Real-Time communication uses the VLAN tag as defined in IEEE
802.1Q.
For demanding communication tasks of high performance within PROFINET, for instance Motion Control, the
Isochronous Real Time (IRT) has been developed. This communication requires specific hardware to establish
integrated switch functionality and cycle synchronization.
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