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An inverse multiplexer (often abbreviated to "inverse mux" or "imux") allows a data stream to be broken into multiple lower data rate communication links. An inverse multiplexer differs from a demultiplexer in that each of the low rate links coming from it is related to the others and they all work together to carry their respective parts of the same higher rate data stream. By contrast, the output streams from a demultiplexer may be completely independent from each other and the demultiplexer does not have to understand them in any way.
Note that this is the opposite of a multiplexer which creates one high speed link from multiple low speed ones.
example:
|--low rate link #1--|
DTE ---high rate data---inverse mux |--low rate link #2--|(de)inverse mux--DTE
|--low rate link #3--|
DTE = Data terminal equipment DCE = Data circuit terminating equipment
This provides an end to end connection of 3 x the data rate available on each of the low rate data links. Note that, as with multiplexers, links are almost always bi-directional and an inverse mux will practically always be combined with its reverse and still be called an inverse mux. This means that the "de-inverse mux" will actually be an inverse mux.
Inverse muxes are used, for example, to combine a number of ISDN channels together into one high rate circuit, where the DTE needs a higher rate connection than is available from a single ISDN connection. This is typically useful in areas where higher rate circuits are not available.
An alternative to an inverse mux is to use three separate links and load sharing of data between them. In the case of IP, network packets could be sent in round robin mode between each separate link. Advantages of using an inverse mux over separate links include
- lower link latency (one single packet can be spread across all links)
- fairer load balancing (computing)
- network simplicity (no router needed between boxes with high speed interfaces)
A simple analogy to transport can help explain the distinction between multiplexing and inverse multiplexing. When small cargoes such as pencils are shipped overseas, they are generally not carried one at a time. Rather, they are assembled into small boxes, which are grouped into larger cartons, which go into intermodal containers, which join multiple containers aboard a container ship. Each step is a multiplexing. Conversely a large cargo, for example in structure relocation, may be disassembled for carriage on multiple vehicles and then reassembled in the correct order at the destination. This is inverse multiplexing.
See also
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