You receive a TELEX with the sender's I.D. of 433863491. What type of terminal sent this message to your vessel?

The terminal that sent the TELEX with the sender's I.D. of 433863491 is an Inmarsat-C terminal. Inmarsat-C is designed for international maritime communication, supporting features such as TELEX messaging. The identification number used for such messages conforms to certain formats that allow users to identify the type of terminal in use. In this case, the I.D. indicates a structure associated with Inmarsat-C, which provides access to TELEX and other communication services over satellites.

Inmarsat-B and Inmarsat-M both provide satellite communication services as well, but they do not align with the specific I.D. format generated by Inmarsat-C terminals for TELEX communication. A land TELEX terminal, while capable of sending messages, would not have the same I.D. format tied to Inmarsat terminals, as it pertains to a terrestrial system rather than a satellite communication network. Hence, recognizing the characteristics of the I.D. confirms that the correct answer identifies the TELEX sender accurately as an Inmarsat-C terminal.