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An inverse multiplexer (IMUX) is a device performing the opposite function of a multiplexer (MUX). Instead of allowing one or more low-speed analog or digital input signals (or data streams) to be selected, combined and transmitted at a higher speed on a single shared medium or within a single shared device, i.e. multiplexing, an inverse multiplexer breaks the combined and related higher speed analog or digital signals into several concurrent lower-speed related signals or data streams. Thus, using multiple slower lines, the data stream can be more evenly distributed across all lines.
The difference between demultiplexing (DMUX) and inverse multiplexing is that the output streams of demultiplexing are unrelated but the output streams of inverse multiplexing are related.
Just as multiplexers are combined with demultiplexers to create bi-directional data flow, inverse multiplexers may be combined with an inverse demux (i.e. the reverse of an inverse multiplexer); however, (as confusing as it sounds) the combination may still be called an inverse multiplexer.
To further explain a complex process with a simple physical transport analogy, cell phones are generally not shipped individually but are rather boxed together. All boxes of cell phones are not generally shipped individually; rather they are loaded on a large truck and shipped to a wholesaler. Each of these steps is multiplexing. At the wholesaler, the truckload of cell phone boxes are broken down into appropriate orders going to multiple retail or individual customer locations on multiple smaller trucks and they are reassembled in the correct order to satisfy retailers and individual customers. This is inverse multiplexing. That is, all the boxes contain cell phones, and thus are related, even though they travel different routes and may have different features, colors, model numbers, etc.
In 2005 inverse multiplexing across eight slower (1.544 Mbps) T1 lines was considered less expensive than renting a faster (45 Mbps) T3 line.