Specifications

22 Rockwell Automation Publication AG-SG001G-EN-P - April 2015
Chapter 2 Choosing a Telemetry Network
Choosing a Topology
Topology is the geometric arrangement of nodes and links that make up a
network. For a SCADA system, choose among point-to-point, point-to-
multipoint, and multipoint-to-multipoint topologies.
Point-to-point
Point-to-point is a communication link between only two stations, where either
station can initiate communication with the other, or one station can inquire and
control the other.
Stations can be connected using:
• cables or permanent public media like leased telephone lines or digital data
services.
• temporary connections, such as dial-up lines or microwave, radio, or
satellite transmissions.
Point-to-point is generally a 2-wire connection, with the transmission media
using two wires for signal transmission/reception. Since a public-switched
telephone network (PSTN) provides a 2-wire connection, the topology used for a
dial-up line is 2-wire point-to-point.
Point-to-multipoint (multidrop)
Point-to-multipoint is a communication link among three or more stations with
one station being a communication arbitrator (master) that controls when the
other stations (remote stations) can communicate.
The stations can be connected using:
• permanent public media like leased lines or digital data services.
• atmospheric connections, such as microwave, radio, or satellite
transmissions.
TIP
Choose this topology if you need a peer-to-peer communication
connection, such as a back-up communication link between
remote stations at a site and the master station at the control site.
Station Station
ModemModem
DTE
DCE DCE
Modem
Modem Modem
Master
Remote Remote