Which keystroke or character is necessary for requesting a direct TELEX call to a shore-based location during ARQ communications?

The correct choice for requesting a direct TELEX call to a shore-based location during ARQ (Automatic Repeat reQuest) communications is the specific format represented in the first option, which is the structured command prefixed with "DIRTLX" followed by the address of the desired shore-based TELEX location and concluded with the "+" character.

This command format is necessary because it enables the communication system to accurately identify that a direct TELEX connection is being requested. The "DIRTLX" is a predefined command that signals the system to initiate a direct TELEX operation. The inclusion of the address (in this case, an example like "023123456") is essential to define the destination of the message. The "+" at the end of the command indicates the completion of the directive, allowing the system to process the request properly.

In contrast, the other options do not follow the required format for direct TELEX communication in ARQ. The second choice "MSG+" refers to sending a message but does not specifically relate to initiating a TELEX call. The third choice "GA+?" is typically used in radio communications to signify "Go Ahead" and inquire if the channel is clear for speech, which is unrelated to TELEX communications. Lastly, "