Configuring Topology - Siemens SIMATIC PROFINET Function Manual

3.3

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.
PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG
Parameter assignment/addressing
3.3 Configuring topology
59