What is Multiplexing
Multiplexing is described by Forouza and Fegan (2007) as a set of procedures used to concurrently transmit several signals over a particular data link. The main goal of multiplexing is efficiency. Different multiplexing techniques are utilized to achieve the desired bandwidth size, increase privacy and reduce jamming. Below are applications that might use different types of multiplexing.
What is Frequency Division Multiplexing (FDM)?
Frequency division multiplexing (FDM) assigns none overlapping frequency to each user hence it allows multiple users to receive transmissions using a single medium (White, 2013). For example, FDM is used in by television stations and cell phone service providers. Both providers may use air as a medium of transmission where FDM is used to assign a set of frequencies known as channels.
FDM partitions communication systems like the four abstract layers of the Open Systems Interconnection (OSI) model. The OSI model partitions communication system among its abstract layers while FDM partitions communication among its user. However, both FDM and OSI are not concerned with interoperability of individual allocations. This means that once FDM and OSI allocates communication channels, they do not dictate or govern how these channels will be used. The main devices using FDMs are TVs, radios and cell phones.
What is Time Division Multiplexing (TDM)?
Contrary to FDM, White (2013) writes that time division multiplexing (TDM) does not allow multiple users to transmit at the same time but rather allocates each user a time frame for transmission. This is achieved by dividing the available transmission time to allow users to take turns transmitting with the available bandwidth. Example of an application that uses TDM is a wire line telephone system which takes advantage of an existing transmission medium to cut on the cost of transmitting each low-bit-stream separately.
What is Dense Wavelength Division Multiplexing (DWDM)?
Dense wavelength division multiplexing (DWDM) is frequency division multiplexing technique that assigns input sources to separate sets of frequencies (White, 2013). This is achieved by use of lasers with different wavelengths for transmitting multiple signals over the same period of time on a single medium. This technique is applied in fiber optic cable transmission. Fiber optic cables are used in local area networks (LAN) and high-speed wide area networks (WAN). The characteristics of application that use DWDM is the diversity in their transmission frequencies. So optic fiber can be used in a network where devices have different frequencies and wavelength.
Multiplexing is concerned with transmitting multiple signals over a data link. Depending on the privacy needed, bandwidth size and possibility of jam occurring, different multiplexing techniques are used for different applications. FDM, for instance, is used in television, radio and cellphone signal transmissions. TDM is used in wired telephone transmission where users take turns transmitting, Finally, DWDM is utilized in fiber optic transmission.
Forouzan, B. A., & Fegan, S. C. (2007). Data communications and networking. 4th ed. New York: McGraw-Hill Higher Education.
White, C. (2013). Data communications & computer networks. 7th ed. Boston: Cengage Learning.