Siemens X-400 ユーザーズマニュアル

Operating Instructions for SCALANCE X-400 Industrial Ethernet Switches 
C79000-G8976-C186-03 

11

 

 

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.