Siemens SIMATIC ET 200AL, System Manual

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Parameter assignment/addressing
3.5 Configuring topology
PROFINET with STEP 7
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Function Manual, 05/2021, A5E03444486-AL
3.5 Configuring topology
Introduction
If an IO device is assigned to an IO controller, this does not yet specify how the ports are
connected to each other.
A port interconnection is not required to use RT, but it provides the following advantages:
•
A set topology is assigned with the port interconnection. Based on an online-offline
comparison, it is possible to conduct a set-actual comparison with all devices that support
this function.
• The "Device replacement without exchangeable medium" function can be used.
A port interconnection is an essential requirement for using IRT.
An overview of various options for setting up a PROFINET network is given below.
Line
All the communication devices are connected in a linear bus topology.
In PROFINET, the linear bus topology is implemented with switches that are already
integrated into the PROFINET devices. Therefore, the linear bus topology at PROFINET is
merely a special form of tree / star topology.
If a link element (switch, for example) fails, communication across the failed link element is
no longer possible. The network is then divided into 2 subsegments.
Linear bus topology structures require the least cabling.
Star
If you connect communication devices to a switch with more than two PROFINET ports, you
automatically create a star network topology.
If an individual PROFINET device fails, this does not automatically lead to failure of the entire
network, in contrast to other structures. It is only if a switch fails that part of the
communication network will fail as well
Tree
If you interconnect several star structures, you obtain a tree network topology.
Ring
In order to increase the availability of a network, use ring structures. In principle, a linear bus
topology is connected to a ring through a so-called redundancy manager.
The task of the redundancy manager is managed by an external switch SCALANCE X, a CPU
that supports the Media Redundancy Protocol MRP (e.g., CPU 1516-3 PN/DP) or a CP (e.g.,
CP 343-1 Lean).
If there is a break in the network, the redundancy manager ensures that the data is redirected
over an alternative network connection in the ring.