sentences:  Two-way simultaneous communications lets the endpoints talk and listen simultaneously.Two-way alternating communications are sometimes called half-duplex, but there may be a fine distinction that two-way alternating communications is a property of the communication protocol used between the endpoints, while the underlying communications medium may support either two-way alternating or two-way simultaneous communications.When the medium is shared for transmitting and receiving, it can only support two-way alternating protocols, and the medium may be called physically half-duplex.