Multiplexing is a technique of combining multiple channels over a transmission path and then recovering or de-multiplexing the separate channels at the receiving end. The basic ways of doing multiplexing are as follows:
- Frequency-Division Multiplexing (FDM) - the carrier bandwidth is divided into sub-channels of different frequency widths, each carrying a signal at the same time in parallel. FDM is used in analog transmission.
- Time-Division Multiplexing (TDM) - the multiple signals are carried over the same channel in alternating time slots. TDM is widely used in digital transmission.
- Code Division Multiplexing (CDM) - each channel transmits its bits as a coded channel-specific sequence of pulses. This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber and asynchronously demultiplxed.
- Wavelength Division Multiplexing (WDM) - multiple signals are carried together as separate wavelengths of light in a multiplexed signal. WDM is used in optical fiber networks. WDM is based on the same principle of FDM but applying to wavelengths of light in optical fiber.
- Coarse Wavelength Division Multiplexing (CWDM) C a variation of WDM. It carries four to eight wavelengths per fiber, sometimes more. Designed for short to medium-haul networks (regional and metropolitan area).
- Dense Wavelength Division Multiplexing (DWDM) C a variation of WDM. A typical DWDM system supports eight or more wavelengths. Emerging systems support hundreds of wavelengths.
A multiplexer is a combinatorial system that is given a certain number (usually a power of two 2n) data inputs, and naddress inputs used as a binary number to select one of the data inputs. The multiplexer has a single output, which has the same value as the selected data input. The multiplexing process may following one of the principles such as TDM, FDM, CDM, or WDM, etc. Multiplexing may take placing in software, where multiple threads of information streams are delivered to a device or process at the same time.
Multiplexing and Multiplexer
Related Terms: TDM, FDM, CDM, WDM, DWDM
Reference Links:
http://www2.rad.com/networks/1999/wdm/wdm.htm: Wavelength Division Multiplexing