1.3.9 Sink And Information Delivery

The sink converts the reconstructed electrical signal into a form usable by the end user or application. This may involve converting a digital bitstream into sound, images, text, or stored data. From the user's perspective, the sink represents the final outcome of the communications process, even though it relies on a sophisticated chain of processing stages to function correctly.

The form taken by the sink depends upon the application. In a telephone, the sink is a loudspeaker that converts electrical signals into sound. In a television or computer monitor, it is a display that reconstructs images and video. In a computer network, the sink may be a software application that stores data on a disk, displays a web page, or processes information received from another computer. Industrial control systems, navigation equipment, and Internet of Things (IoT) devices may also act as sinks, interpreting received information to control machinery or initiate other actions.

In many modern communications systems, the sink is not a human user but another electronic system. For example, computers routinely exchange files without human intervention, sensors continuously transmit measurements to remote monitoring systems, and automated control systems exchange commands in real time. Regardless of whether the recipient is a person or a machine, the objective remains the same—to recover the transmitted information accurately and present it in a form that can be used effectively.

The more-detailed model exposes the layered structure that underpins modern digital communications systems. Although practical systems differ greatly in complexity and implementation, they all perform the same sequence of fundamental operations: information is generated, represented efficiently, protected against errors, transmitted across a communications channel, recovered at the receiver, and finally delivered to its intended destination. In Chapters 2 to 12, each of these functional blocks is examined in more detail, beginning with the properties of signals themselves and progressing through the techniques used to represent, transmit, protect, and share information over practical communications channels.