Transmission Procedures And Real-Time Response - Siemens SIMATIC NET System Manual

1.2.4

Transmission procedures and real-time response

Overview
Non real-time communication (NRT communication)
NRT communication is non-time -critical communication and corresponds to the
communication of Industrial Ethernet with the protocol family TCP/IP. Everything that is
transferred using Industrial Ethernet can also be transferred via PROFINET, for example
HTTP, TCP, UDP, SNMP, ARP.
Real-time communication (RT communication)
Real time means that a system processes external events within a specific time. If the
reaction is predictable, this is known as a deterministic system.
A high data rate alone is no guarantee for real-time response, since delays are possible at
"bottlenecks" in the network. Instead, the network protocol must ensure that time critical
frames are given preferential treatment.
The RT communication is suitable for transfer of alarms and cyclic data. Special switches
must be used here. All SIMATIC NET switches are suitable for this. There is, however, not
yet any need for particular communication planning in the form of a special configuration.
In RT communication, the cyclic data are transferred between the IO controller and IO device
but without the "best possible synchronicity".
Unsynchronized IO devices automatically exchange data using the RT communication.
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Basics of communication with Industrial Ethernet
1.2 Industrial Ethernet
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