Siemens SIMATIC NET System Manual page 51

● Separating load
By filtering the data traffic based on the Ethernet (MAC) addresses, local data traffic
remains local. The data is distributed to all ports/network nodes using the direct switching
method. Only data intended for nodes in other subnetworks is switched from the input
port to the appropriate output port of the switch. To make this possible, a table assigning
Ethernet (MAC) addresses to output ports is created by the switch in a "teach-in" mode.
● Limiting errors to the affected subnetwork
By checking the validity of a data packet on the basis of the checksum which each data
packet contains, the switch ensures that faulty data packets are not transported further.
Collisions in one network segment are not passed on to other segments.
Advantages of switched LANs
The advantages of such switched LANs are:
● Good performance (since the messages only block the sections of cable actually between
the sender and receiver),
● Avoidance of data collisions because a sender does not block the entire network
● Increased protection against failure, particularly in topologies that include redundancy,
If a connection path is blocked in a redundant topology (due to a cable break or
component failure), switches can still redirect the messages over an alternative path and
maintain communication. A network with a ring topology (see below) is a classic example
of using switches in this way.
● Possibility of forming subnetworks and network segments,
● Simple rules for network configuration,
● Simple expansion of existing networks
Application example: Redundant ring
Using an IE Switch as the redundancy manager in a ring with a redundancy manager
(Page 79) provides greater availability. If there is an interruption on the connection between
these switches, the IE switch used as redundancy manager acts like a switch and in a very
short time creates a line (bus) from the ring. As a result, a functional, end-to-end structure is
restored.
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Basics of communication with Industrial Ethernet
1.4 Switches and switched LANs
51