User manual

Chapter Two Operation
MAN_905G_1.16 Page 26
comms problem (this means that the corresponding update time for the input at the 905U will
need to be short). If the point is an output, then the update time for the output should be
made short.
2.7 Security Considerations
There are three dimensions of security considerations:
1. Failure to operate when required - or “operational reliability”.
The features discussed above optimize operating reliability. Using an acknowledgment
and re-try protocol ensures that the transmitting module is aware whether the transmitted
message has been transmitted reliably. The “comms fail” alarms provide indication if the
radio link has failed to operate.
2. Mal-operation, or operating when not requested.
This problem occurs when an output is “triggered” by the wrong radio device. The 905G
modules use frequency encoding and a very secure addressing system to ensure this does
not occur. An additional security level using data encryption can also be selected.
3. Malicious operation, or “hacking”
This is the problem most associated with security concerns - the ability for someone to
access information from a radio system by “listening-in”, or to cause damage by
transmitting radio messages to force outputs.
A security option can be selected during the module configuration to protect against this.
The security option (if selected) adds data encryption to radio messages. Modules in the
same system are automatically configured with the encryption key, such that only these
modules can understand each other. “Foreign” modules will hear the messages, but
cannot decrypt the messages. For more information, refer to section 4.2.2.