A block diagram is a representation of a system where the principal parts or functions are represented by blocks connected by lines that shows the relationships of the blocks. A block diagram of a communication system displays a structural representation of a computer system as it gives a quick overview of the working process of a computer from inputting the data to retrieve the desired results. As shown, a multiplexer is a sequential circuit designed to accept multiple inputs. The common port and the output of the two filters (RX and TX) form the three terminals of the diplexer. Signals applied to common ports are separated in accordance with their passband frequencies of the filters.