Multiplexers

A multiplexer (or mux; occasionally the term muldex is also found, for a combination multiplexer-demultiplexer) is a device that encodes or multiplexes information from two or more data sources into a single channel. more...

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In electronics, multiplexers function as multiple-input, single-output switches. A multiplexer has multiple inputs and a selector that connects a specific input to the single output. The schematic symbol for a multiplexer is an isosceles trapezoid with the longer parallel side containing the input pins and the short parallel side containing the output pin. The schematic on the right shows a 2-to-1 multiplexer on the left and an equivalent switch on the right. The sel wire connects the desired input to the output.

In digital signal processing (DSP), the multiplexer takes several separate digital data streams and combines them together into one data stream of a higher data rate. This allows multiple data streams to be carried from one place to another over one physical link, which saves cost.

Cost savings

One use for multiplexers is cost savings by connecting a multiplexer and a demultiplexer (or demux) together over a single channel (by connecting the multiplexer's single output to the demultiplexer's single input). The image to the right demonstrates this. In this case, the cost of implementing separate channels for each data source is more expensive than the cost and inconvenience of providing the multiplexing/demultiplexing functions. In a physical analogy, consider the merging behaviour of commuters crossing a narrow bridge; vehicles will take turns using the few available lanes. Upon reaching the end of the bridge they will separate into separate routes to their destinations.

At the receiving end of the data link a complementary demultiplexer or demux is normally required to break single data stream back down into the original streams. In some cases, the far end system may have more functionality than a simple demultiplexer and so, whilst the demultiplexing still exists logically, it may never actually happen physically. This would be typical where a multiplexer serves a number of IP network users and then feeds directly into a router which immediately reads the content of the entire link into its routing processor and then does the demultiplexing in memory from where it will be converted directly into IP packets.

It is usual to combine a multiplexer and a demultiplexer together into one piece of equipment and simply refer to the whole thing as a "multiplexer". Both pieces of equipment are needed at both ends of a transmission link because most communications systems transmit in both directions.

A real world example is the creation of telemetry for transmission from the computer/instrumentation system of a satellite, space craft or other remote vehicle to a ground system.

Read more at Wikipedia.org