Final answer:
Full duplex is the transmission method that allows simultaneous two-way communication over a medium. It differs from half duplex which requires switching between sending and receiving, and is not the same as multiplexing, which combines multiple signals.
Step-by-step explanation:
The method of transmission that allows signals to travel in both directions over a medium simultaneously is called full duplex. This means that two-way communication can occur at the same time, without the need to switch between sending and receiving modes. An example of full duplex communication is a telephone conversation where both parties can talk and listen at the same time. The other options provided, such as half duplex, allow communication in both directions but not simultaneously - they require switching between transmitting and receiving.
Multiplexing, on the other hand, refers to a technique where multiple signals are combined into one signal over a shared medium. While it can be used in conjunction with full duplex communication, it is not a method that defines how signals travel direction-wise over a medium.