rtc0

Rtc0 is a protocol used for communication between a server and its Remote Terminal or User Terminal. It stands for Request to Communicate. In the context of IBM mainframe systems, rtc0 is a control code used to initiate communication between the server and the terminal.

When a user at a Remote Terminal initiates communication with the server, the server responds with an rtc0 message, signaling the user to "ready to communicate". This message is typically sent as an 00h code at the beginning of a frame, and its purpose is to acknowledge the receipt of the user's previous message and indicate that the server is ready to accept and respond to the user's next message.

Rtc0 protocol involves a series of interactions, including handshake sequences and data exchange, all taking place between the server and the Remote Terminal or User Terminal. The server sends its first message as a response to the user's message, containing a reply to the user's request. However, this first message is often distinguished as "server to terminal (ST) beginning of message data", not requiring user initialization. The remote terminal must send a responsive message for the connection to become fully operational.

Significance of rtc0 extends to performance-oriented multi-user systems, where controlling the "ready to communicate" establishment facilitates timely synchronization and permits greater efficiency and volume of inter-system communication. In other multi-tasking systems, the system resources are optimized for many users to use the system at once; accordingly, mainframe Rtc0 plays a similar problem-solving role.