RTU Communications Strategies
In a theoretical Radio Telemetry Monitor and Control System the System Control Computer (SCC) communicates to
each Remote Terminal Unit (RTU) directly and receives a direct answer. This is a Point-to-Point communication
scheme and actually occurs in very few SCADA systems. See graphic below.
The above graphic could also represent a Master-to-Slave communication scheme in a Radio Telemetry System.
The Master or SCC must ask or poll each slave RTU for information and the slave RTU can only respond when polled by
the Master - i.e., a high speed poll-around by the Master. Unsolicited messaging which is a slave RTU sending a message without
being polled is not allowed. Multiple path routing or Master to slave RTU #1 forwarding a message to slave RTU #2 is not possible.
The constant master-to-slave poll around requires 100% of the radio channel.
The DFA Telemetry System uses an exception based communication strategy. If a monitored value
at a remote site changes, the RTU calls into the System Control Computer (SCC) automatically updating the System's values.
This is known as unsolicited messaging which reduces the amount of radio traffic on the communications channel to the levels
the Federal Communications Commission (FCC) recommends of approximately 20%.
The DFA Telemetry System also allows for multiple path routing of RTU messages. This enables the RTU to use a
Peer-to-Peer communication scheme with store and forward
messaging or message repeating from RTU to RTU or peer to peer.
Most systems can not use a point-to-point communication scheme and usually require some type of message repeating
in the communication scheme.
|
|
|
