RTU: Short for remote terminal unit. In SCADA systems, an RTU is a device installed at a remote location that collects data, codes the data into a format that is transmittable and transmits the data back to a central station, or master. An RTU also collects information from the master device and implements processes that are directed by the master. RTUs are equipped with input channels for sensing or metering, output channels for control, indication or alarms and a communications port.
MTA: Short for message transfer agent, the program responsible for receiving incoming e-mails and delivering the messages to individual users. The MTA transfers messages between computers. Hidden from the average user, it is responsible for routing messages to their proper destinations. MTAs receive messages from both MUAs and other MTAs, although single-user machines more often retrieve mail messages using POP.
MUA: Short for mail user agent,
the software that allows a user to access and manage e-mail, including
reading, composing, disposing, printing and displaying e-mail messages.
The MUA provides the interface between the user and the MTA. Eudora and
Outlook are two popular MUAs.