1MRS751852-MUM
SYS 600 *9.0
33
MicroSCADA Pro
System Overview
Technical Description
4.1.3.
Network topologies
Most of the communication protocols implemented in MicroSCADA are so called
master-slave protocols. The master is the primary station controlling the data
requests and sending the command. The slave is the secondary station sending data
to the master, either when requested or spontaneously, and executing commands
sent by the master.
Some protocols, for example DNP V3.00, also support so called peer-to-peer
communication, which means that slaves can communicate directly with each other.
The number of masters and slaves connected to one communication line is limited
by the protocol used. In practice the limitation is set by required performance and
response. The more devices are connected to one line, the more bandwidth the
communication requires.
There are several possibilities how to connect the master and the slave, or slaves.
The direct topology (point-to-point) can be a direct physical cable from point-to-
point or a two-node radio, or modem network. The serial bus topology (multi-drop)
is commonly made up of many modems with their outputs/inputs tied together, or
by using a star-coupler. Figure 4.1.3.-1 illustrates these network topologies.
topologies
Fig. 4.1.3.-1
Point-to-point and serial bus topologies
A special type of a multi-drop communication is a communication loop, which is
described in Figure 4.1.3.-2. A communication loop is a type of multi-drop
communication where the line forms a loop. This means that there is always an
alternative line leading to a node, even if a line is broken. Redundancy is achieved
without duplicating the lines.
