Multiplexing in Data Communications + Types + Difference

Multiplexing in Data Communications where we use it.

Multiplexing is the technique of transferring multiple signals over a single shared line or a media. For example, several telephone calls may be carried using one wire. The main aim of using this technique is to share the resources (Media) of network.

Multiplexing:

Two or more simultaneous transmission on a single circuit. Transparent to end users. Where multiplexing costs less.

Types of multiplexing.

1. TDM
   Synchronous TDM (T-1, ISDN, optical fiber)
   Statisical TDM (LAN's)
2. FDM (Cable, Cell Phones, Broadband)
3. WDM (Optical Fiber)
4. CDM (Cell Phones)

Frequency Division Multiplexing

• Assignment of non-overlapping frequency ranges to each user or signal on a medium. Thus al signals are transmitted at the same time, each using different frequencies.
• A multiplexer accepts inputs and assigns frequencies to each device.
• The mutliplexor is attached to a high-speed communications line.
• A corresponding multiplexer, or De-multiplexer is on the end of high-speed line and separates the multiplexed signals.

Time Division Multiplexing

Read about Time Division Multiplexing

Synchronous Time Division Multiplexing

• The original time division multiplexing
• The multiplexer accepts input from attached devices in a round-robin fashion and transmit the data in a never ending pattern.
• T1 and ISDN telephone lines are common examples of synchronous time division multiplexing.

If one device generates data at a faster rate than other devices, then the multiplexer must either sample the incoming data stream from that device more often than it samples the other devices, or buffer the faster incoming stream.

If a device has nothing to transmit, the multiplexer must still insert a piece of data from that device into the multiplexed stream.

Statistical Time Division Multiplexing

A statistical multiplexer does not require a line over as high a speed line as synchronous time division multiplexing since STDM does not assume all sources will transmit all of the time.

Good for low bandwidth lines (used for LAN's)

Wavelength Division Multiplexing (WDM)

• Give each message a different wavelength (frequency).
• Easy to do with fiber optics and optical sources.

Code Division Multiplexing (CDM)

• Also known as code division multiple access (CDMA).
• An advanced technique that allows multiple devices to transmit on the same frequencies at the same time using different codes.
• Used for mobile communications.

Difference in Multiplexing and DeMultiplexing