Network Topologies; Basics Of Ethernet Switching - Siemens SCALANCE X-300 Series Operating Instructions Manual

Network topologies

3.1

Basics of Ethernet switching

Ethernet switching
Ethernet switches forward data packets directly from the input port to the appropriate output
port during data exchange based on the address information. Ethernet switches operate on a
direct delivery basis.
Essentially, switches have the following functions:
● Connecting collision domains / subnets
Since repeaters and star couplers (hubs) operate at the physical level, their use is restricted
to the span of a collision domain. Switches connect collision domains. Their use is therefore
not restricted to the maximum span of a repeater network. On the contrary, extremely large
networks with very large spans are possible with switches. The distances achieved depend
on the fiber-optic interfaces used in the devices and the FO fibers used (see technical
specifications).
● Load containment
By filtering the data traffic based on the Ethernet (MAC) addresses, local data traffic remains
local. In contrast to repeaters or hubs, which distribute data unfiltered to all ports / network
nodes, switches operate selectively. Only data intended for nodes in other subnets 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 the propagation of errors to the subnet involved.
By checking the validity of a data packet on the basis of the checksum which each data
packet contains, the switch ensures that bad data packets are not transported further.
Collisions in one network segment are not passed on to other segments.
The need for Industrial Ethernet switches
With over 95% of LANs based on Ethernet, this is the most commonly used technology. The
use of switches is particularly important: They allow extensive networks with large numbers of
nodes to be set up, increase the data throughput, and simplify network expansion.
The IE Switches X-300 from SIMATIC NET are designed for use in high-speed plant networks
that will also meet future requirements. With the HRP redundancy function and standby linking
of rings, high network availability can be achieved. HRP and standby link reconfigures the
network within 300 ms. Support of IT standards such as VLAN, RSTP, IGMP, and GARP makes
seamless integration of automation networks in existing office networks possible.
The IE Switches X-300 are designed for use in switching cubicles and cabinets.
SCALANCE X-300
Operating Instructions, 11/2019, A5E01113043-24
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