Siemens X-400 - Manual (Page 11)

Operating Instructions for SCALANCE X-400 Industrial Ethernet Switches
C79000-G8976-C186-03
11
Introduction to
Industrial Ethernet Switches
1
1.1 Basic Information
Switching
With switching technology, data packets are forwarded directly from the input port
to the appropriate output port during data exchange based on the address informa-
tion. Switches operate on a direct delivery basis.
Essentially, switches have the following functions:
● Connection of Collision Domains / Subnets
Since repeaters and star couplers (hubs) operate at the physical level, their use
is restricted 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, switches allow extremely large networks with spans of 150 km
to be set up and when using LD modules, even up to 1300 km.
● Containing Load
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 unfil-
tered to all ports / network nodes, switches operate selectively. Only data in-
tended for nodes in other subnets is switched from the input port to the appro-
priate 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.
● Limitation of Errors to the Network Segment Affected
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.