Siemens SCALANCE X-200 Configuration Manual page 31

Keeping network load within limits
To allow you to limit the network load resulting from extremely short update times, update
groups are configured for the IRT data. If only a few devices require the shortest update
times, these are assigned to the first update group. Each further update group has n times
the update time of the previous group, where n can be configured. This means that the data
is updated less frequently and the network load is reduced.
In STEP 7 V5.4, only one update group is planned.
IRT runs alongside real-time and TCP/IP communication
Apart from IRT communication for which a fixed bandwidth is reserved within the update
time, RT communication and TCP/IP communication are also permitted within the update
time.
In RT communication (real-time communication), the cyclic data is transferred between the
IO controller and IO device, however, without the best possible synchronicity.
Unsynchronized IO device automatically exchange data using RT communication.
Since TCP/IP communication is also possible, other non real-time data or
configuration/diagnostic data can be transported.
SCALANCE X-200
Configuration Manual, 03/2015, C79000-G8976-C285-06
IRT communication with X-200
31