SECTION 3
um_tslm rev3.doc
Page 10 of 62
3.2.1
Point-to-Point
A point-to-point network is the simplest of all networks, and may be used for
connecting a pair of PC's, a host computer and a terminal, a SCADA master
and one remote, mobile applications like in-vehicle GPS receivers to base
stations, or a wide variety of other networking applications.
3.2.2
Point-to-Multipoint
A Point-to-Multipoint network is a common network type used in SCADA or
other polling systems. The single master station communicates with any
number of remotes and controls the network by issuing polls and waiting for
remote responses. Individual remotes (DTE) manage addressing and respond
when their individual addresses are queried. The DTE unit addresses are
maintained in a scanning list stored in the host program or master terminal
device at the SCADA host site. The communications equipment is transparent
and does not interact with specific remotes; all data is coupled to the host on
a single data line (such a network is commonly used with synchronous radio
modems and asynchronous radio modems).
3.2.3
Multiple Point-to-Point
A multiple point-to-point is similar to the point-to-multipoint system except
the SCADA host has multiple serial ports that are directed to different
geographic areas in the SCADA system.
3.2.4
Peer-to-peer
A Peer-to-Peer network is generally used for device to device communications
among a number of stations. This network requires full addressing capability
on the part of the data equipment (DTE). If the distances involved for any link
or links are too great for a single radio hop, they can be extended by means
of repeaters without affecting the basic network design.
3.2.5
Store and Forward
Store and Forward is a common technique where a data transmission is sent
from one device to a receiving device but first passes through a relaying
device. The device is typically an RTU or PLC used by the message service to
store the received message then it transmits the message to the intended
recipient.