It was initially designed by Mentec for use in its own Remote Terminal Units. The first 5 bits are the address of the Remote Terminal that is responding. This is known as the Remote Terminal Unit (RTU) number. By contrast, the 2741 was primarily focused on remote terminal applications. An emergency callbox can also have a secondary function as a remote terminal unit (RTU). The Remote Terminal Unit (RTU) connects to physical equipment. SFTP/SCP file transfers and remote terminal connections are popular use cases for an SSH server. A variant of PLCs, used in remote locations is the remote terminal unit or RTU.