Multiplexing in Computer Networks
The process of sharing a medium or bandwidth is called multiplexing. This procedure involves combining signals from various sources and sending them via a single physical or communication channel. A device called a multiplexer, or MUX, performs multiplexing in computer networks by converting 'n' input lines into a single output line.
However, a device known as a DEMUX (demultiplexer) may take a single input line and produce 'n' output lines. Demultiplexing is the process of delivering received segments to the appropriate app layer operations at the receiver side.
Diagram of Multiplexing
A multiplexer is used to transmit the 'n' input lines seen above, combining the signals to create a composite signal. These signals are now routed to their appropriate locations after passing through DEMUX.
Types of Multiplexing in Computer Networks
Multiplexing falls under the following categories:
- Frequency Division Multiplexing (FDM)
- Time-Division Multiplexing (TDM)
- Wavelength Division Multiplexing (WDM)
1. Frequency Division Multiplexing (FDM)
This involves many signals being sent simultaneously, with each source sending its signals within the designated frequency range. To prevent overlapping, there is an appropriate frequency difference between the two nearby signals. The likelihood of a collision is reduced because the signals are sent at the designated frequencies.
Each user believes they have a certain bandwidth within the multiple logical channels that make up the frequency spectrum. Several signals are transmitted concurrently, each of which is assigned a different frequency band or channel. It is employed in TV and radio broadcasting.
Benefits of Frequency Division Multiplexing (FDM)
- The procedure is straightforward and simple to modify.
- The high-speed line's end has a matching multiplexer or de-multiplexer that separates the multiplexed signals.
- Analog signaling is used to send the signals for frequency division multiplexing.
Drawbacks of Frequency Division Multiplexing (FDM)
- FDM's inability to fully utilize the cable's capacity is one of its drawbacks.
- Avoiding overlap between the frequency bands is crucial.
- To prevent signals from one band from influencing signals in another, there needs to be a significant distance between the frequency bands.
2. Time Division Multiplexing (TDM)
This occurs when each signal is given a specific amount of time and the media's data transmission rate exceeds the source's. Because of how tiny these spaces are, all transmissions seem to be parallel. In time-division multiplexing, all of the signals operate with the same frequency at different times, but in frequency division multiplexing, all of the signals operate simultaneously with distinct frequencies.
The two categories of TDMs are as follows:
- Synchronous TDM
- Asynchronous TDM
a). Synchronous TDM
The time slots have been predetermined and assigned. This time slot is even assigned in the event that the source does not currently have data ready. The slot is sent empty in this scenario. It is employed for digital voice stream multiplexing.
b). Asynchronous TDM
Asynchronous Time Division Multiplexing is a type of multiplexing in which the sampling rate is varied and does not require a general clock. The bandwidth of asynchronous TDMs is often low. This kind of TDM allows other devices to use its time slot when there is nothing to send.
Benefits of Time Division Multiplexing (TDM)
- TDM is perfect for applications requiring the transmission of several signals since it can handle a large number of signals over a single communication channel.
- For many applications, TDM is a cost-effective solution since it is an easy-to-implement, relatively straightforward approach.
- In order to guarantee correct signal transmission, TDM necessitates exact time synchronization between the transmitting and receiving devices.
- Because time slots could be left empty if there are no signals to send during a specific time slot, TDM might not utilize available bandwidth to its fullest potential.
- TDM is more costly to install than FDM because it needs complex hardware or software to guarantee exact time synchronization between the transmitting and receiving devices.
- Time jitter, which happens when the time of the sending and receiving devices deviates from synchronization and results in mistakes in signal transmission, might affect TDM.
3. Wavelength Division Multiplexing
The working frequencies are significantly higher here—in fact, they are in the optical range—but otherwise it is the same as FDM applied to fibers. Fibers have a lot of potential because of their enormous bandwidth. A diffraction grating prism is used to pass fibers with various energy bands, divided at the destination after being combined on the long-distance link. It has a very big capacity and is quite reliable.
Benefits of Wavelength Division Multiplexing (WDM)
- By employing several light wavelengths, WDM dramatically expands the volume of data that can be sent over a single fiber optic line.
- It lowers infrastructure costs by enabling network capacity expansion without the need to install more fiber optic lines.
- Because wavelengths are independent of one another, data integrity is preserved across channels.
- Higher-capacity DWDM systems may be vulnerable to temperature fluctuations, necessitating close observation and management.
- When it comes to implementation, DWDM systems can be more complicated than older WDM systems.
- Compared to more straightforward WDM systems, DWDM systems could be more expensive initially.
