Multiplexing jams multiple signals into one medium

How many signals share one path

A cable or radio channel has limited capacity, but it does not have to carry just one conversation at a time. A multiplexer (mux) organizes several input streams so they can travel through the same physical link. At the receiving end, a demultiplexer (demux) uses the same organization rules to recover each stream and route it onward.

The crucial trick is keeping the streams distinguishable. A mux might assign each one a different slice of the link’s capacity, or take turns sending small pieces of each. In fiber-optic systems, separate streams can use different colors—meaning different wavelengths—of light. These approaches are forms of multiplexing; they share a medium without simply blending the information together.

The receiver must know the pattern

In time-division multiplexing, for example, the sender gives each stream recurring turns. It may transmit a brief piece of stream A, then B, then C, and repeat. The demux tracks that timing and directs each piece to the correct output. With frequency-division multiplexing, streams occupy separate frequency bands, which the receiver filters apart. In either case, sender and receiver must agree on the arrangement; otherwise, pieces can be assigned to the wrong stream.

Real systems also need room for framing and control information—the cues that mark boundaries and help the receiver stay synchronized. If a link has more traffic than it can carry, multiplexing cannot create extra capacity: the system must allocate turns or bandwidth, buffer data, or delay or drop some traffic.

Why the arrangement matters

Sharing a link can avoid running a separate cable or reserving a whole channel for every stream. It is one reason a single fiber, radio channel, or network connection can serve many users and applications. The tradeoff is coordination: the more streams share the path, the more carefully the system must schedule, label, and recover their data. The mux packs the traffic together; the demux makes sure it arrives as the separate conversations it was meant to be.