Which mode allows for simultaneous data transmission between sender and receiver?

Full-duplex is the mode that allows for simultaneous data transmission between the sender and the receiver. In a full-duplex communication system, both parties can send and receive messages at the same time, effectively allowing for two-way communication without interruptions. This is akin to a phone conversation where both people can speak and listen simultaneously, resulting in a more natural and efficient exchange of information.

In contrast, simplex mode allows data transmission in only one direction, meaning the sender can only send data while the receiver can only receive data—like a keyboard sending data to a computer without the computer sending any data back. Half-duplex mode allows for two-way communication but not simultaneously; when one side is sending, the other must wait to respond—similar to a walkie-talkie where one person speaks while the other listens and vice versa. Serial transmission, while a method of sending data one bit at a time, does not specify the directionality or simultaneity of communication, making it less relevant to the question of simultaneous data transmission.