Multiplexer (MUX)

Definition of Multiplexer (MUX) in Network Encyclopedia.

What is MUX (Multiplexer)?

A multiplexer is a telecommunications device that multiplexes several data channels from different pieces of data terminal equipment (DTE). Multiplexers (MUXes) are frequently used to combine digital lines in order to save cost by eliminating the need for extra line termination devices such as CSU/DSUs (Channel Service Unit/Data Service Units).

For example, a T1 MUX might have several V.35 interfaces for accepting incoming data from bridges or routers connected to your local area networks (LANs) plus a DSX-1 interface for connecting to a channel bank or private branch exchange (PBX) system.

How does Multiplexer work?

The MUX takes the serial data input and voice input and multiplexes them together into a single data stream using an integrated CSU/DSU for direct transmission over a T1 line, allowing you to use your T1 line for voice and data combined. You can use a similar device to multiplex data and voice for transmission over a public frame relay carrier network.

MUXes are often used in mainframe environments for connecting remote terminals to async hosts without the need for individual cabling for each terminal. These types of MUXes are generally used in pairs and combine channels using time-division multiplexing (TDM). Examples include the following:

  • Fiber-optic MUXes for combining several sync or async data channels onto one duplex fiber-optic cable. A typical fiber-optic MUX might have 12 or 24 RS-232 input ports and support speeds in excess of 115.2 Kbps per channel. These MUXes are typically used in pairs to connect remote terminals to an async mainframe host across a campus environment and are often referred to as short-haul or local MUXes.
  • Twisted-pair MUXes for multiplexing several RS-232 serial channels over installed RJ-11 wiring to save costs.
  • Coax MUXes for connecting several 3270 terminals to an IBM controller in order to reduce the costs of cabling.

You can use an Ethernet MUX to take the output of several ports from a 10-Mbps Ethernet switch and transmit the time-division multiplexed signals over a single fiber-optic cable at distances up to 2 kilometers. These MUXes are also typically used in pairs.


Inverse multiplexer

An inverse multiplexer, or IMUX, takes a single input data channel from a DTE such as a router and spreads it to several digital transmission lines. A demultiplexer is a MUX at the remote end of a multiplexed communication system.

Advanced T1 MUX

Advanced T1 MUXes often offer some management functions. For example, you can configure a MUX with Simple Network Management Protocol (SNMP) to send a trap to your SNMP management console when a problem occurs. Some MUXes can also remote-dial a number using a built-in modem. A modular MUX allows you to expand your wide area network (WAN) link as your network grows by adding modules to provide additional V.35, RS-232, or RS-530 input ports.


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