Multiplexing techniques in Computer Networks - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is multiplexing in computer networks?

Multiplexing is a method that allows multiple signals or data streams to share a single communication channel or medium at the same time, increasing efficiency.

beginner

Name the three main types of multiplexing techniques.

The three main types are Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), and Wavelength Division Multiplexing (WDM).

beginner

How does Time Division Multiplexing (TDM) work?

TDM divides the channel into time slots. Each user or signal gets a specific time slot to send data, one after another, so they share the channel without overlapping.

beginner

What is Frequency Division Multiplexing (FDM)?

FDM splits the channel into different frequency bands. Each signal uses a unique frequency band to send data simultaneously without interference.

intermediate

Where is Wavelength Division Multiplexing (WDM) commonly used?

WDM is used in fiber optic communication. It sends multiple light signals at different wavelengths (colors) through the same fiber to increase data capacity.

Which multiplexing technique divides time into slots for each user?

A Time Division Multiplexing (TDM)

B Frequency Division Multiplexing (FDM)

C Wavelength Division Multiplexing (WDM)

D Code Division Multiplexing (CDM)

TDM assigns different time slots to users so they share the channel one after another.

In Frequency Division Multiplexing, how are signals separated?

A By different time slots

B By different frequency bands

C By different wavelengths

D By different codes

FDM separates signals by assigning each a unique frequency band.

Which multiplexing technique is mainly used in fiber optic cables?

A Time Division Multiplexing

B Frequency Division Multiplexing

C Space Division Multiplexing

D Wavelength Division Multiplexing

WDM uses different light wavelengths to send multiple signals through one fiber optic cable.

What is the main benefit of multiplexing?

A It increases the number of channels needed

B It separates signals by physical distance

C It allows multiple signals to share one channel efficiently

D It slows down data transmission

Multiplexing lets many signals share a single channel, making communication more efficient.

Which multiplexing technique assigns unique codes to separate signals?

A Code Division Multiplexing

B Frequency Division Multiplexing

C Time Division Multiplexing

D Wavelength Division Multiplexing

Code Division Multiplexing (CDM) uses unique codes to separate signals, unlike TDM or FDM.

Explain the difference between Time Division Multiplexing and Frequency Division Multiplexing.

Think about how the channel is shared in time versus frequency.

Describe a real-life example where multiplexing improves communication efficiency.

Consider how many people or devices use one connection at the same time.

Practice

1. What is the main purpose of multiplexing in communication systems?

easy

A. To allow multiple signals to share a single communication channel

B. To increase the power of a single signal

C. To encrypt data for secure transmission

D. To convert analog signals to digital signals

Solution

1. Step 1: Understand the concept of multiplexing

   Multiplexing is a technique used to combine multiple signals so they can share one communication channel efficiently.

2. Step 2: Identify the main purpose

   The main goal is to use the channel efficiently by allowing many signals to use it simultaneously, not to increase power, encrypt, or convert signals.

3. Final Answer:

   To allow multiple signals to share a single communication channel -> Option A

4. Quick Check:

   Multiplexing = sharing channel [OK]

Hint: Multiplexing means many signals, one channel [OK]

Common Mistakes:

• Confusing multiplexing with encryption
• Thinking multiplexing increases signal power
• Mixing multiplexing with signal conversion

2. Which of the following is the correct abbreviation for Time Division Multiplexing?

easy

A. TDM

B. FDM

C. WDM

D. CDM

Solution

1. Step 1: Recall common multiplexing abbreviations

   Time Division Multiplexing is abbreviated as TDM, Frequency Division Multiplexing as FDM, Wavelength Division Multiplexing as WDM, and Code Division Multiplexing as CDM.

2. Step 2: Match abbreviation to full form

   Since the question asks for Time Division Multiplexing, the correct abbreviation is TDM.

3. Final Answer:

   TDM -> Option A

4. Quick Check:

   Time Division Multiplexing = TDM [OK]

Hint: T for Time in TDM helps remember [OK]

Common Mistakes:

• Mixing TDM with FDM
• Confusing WDM with CDM
• Assuming CDM stands for Time Division

3. Consider a communication system using Frequency Division Multiplexing (FDM) with 3 channels at frequencies 100 MHz, 110 MHz, and 120 MHz. Which statement is true?

medium

A. Channels transmit one after another in time slots

B. Channels use unique codes to transmit simultaneously

C. All channels transmit at the same time but on different frequencies

D. Channels combine wavelengths to send data

Solution

1. Step 1: Understand Frequency Division Multiplexing (FDM)

   FDM assigns different frequency bands to each channel so they can transmit simultaneously without interference.

2. Step 2: Analyze the given frequencies and options

   The channels at 100 MHz, 110 MHz, and 120 MHz transmit at the same time but on different frequencies, unlike time division or code division multiplexing.

3. Final Answer:

   All channels transmit at the same time but on different frequencies -> Option C

4. Quick Check:

   FDM = simultaneous different frequencies [OK]

Hint: F in FDM means frequency, so different frequencies [OK]

Common Mistakes:

• Thinking FDM uses time slots
• Confusing FDM with CDM code usage
• Assuming wavelength combination applies here

4. A student wrote that in Time Division Multiplexing (TDM), all channels transmit simultaneously on different frequencies. What is the error in this statement?

medium

A. TDM combines wavelengths for transmission

B. TDM uses different codes, not frequencies

C. TDM is only used for analog signals

D. TDM transmits signals one after another in time slots, not simultaneously

Solution

1. Step 1: Review how Time Division Multiplexing works

   TDM divides time into slots and assigns each channel a slot to transmit sequentially, not simultaneously.

2. Step 2: Identify the mistake in the student's statement

   The student incorrectly said channels transmit simultaneously on different frequencies, which describes FDM, not TDM.

3. Final Answer:

   TDM transmits signals one after another in time slots, not simultaneously -> Option D

4. Quick Check:

   TDM = sequential time slots, not simultaneous [OK]

Hint: TDM means time slots, not simultaneous frequencies [OK]

Common Mistakes:

• Confusing TDM with FDM
• Assuming TDM uses codes or wavelengths
• Thinking TDM only works for analog signals

5. In a fiber optic system using Wavelength Division Multiplexing (WDM), four data streams are combined using wavelengths 850 nm, 1310 nm, 1550 nm, and 1625 nm. If one wavelength channel fails, what is the best approach to maintain communication without losing all data?

hard

A. Switch all data streams to a single wavelength immediately

B. Use redundancy by adding backup wavelengths for critical data streams

C. Convert WDM to TDM to avoid wavelength failure

D. Increase the power of the remaining wavelengths to cover the lost one

Solution

1. Step 1: Understand Wavelength Division Multiplexing (WDM) and failure impact

   WDM uses different light wavelengths to carry separate data streams. If one wavelength fails, that data stream is lost unless there is backup.

2. Step 2: Evaluate options to maintain communication

   Adding backup wavelengths (redundancy) for critical streams ensures communication continues even if one channel fails. Switching all streams to one wavelength or increasing power won't solve the failure. Converting to TDM is not practical on the fly.

3. Final Answer:

   Use redundancy by adding backup wavelengths for critical data streams -> Option B

4. Quick Check:

   WDM failure needs backup wavelengths [OK]

Hint: Backup wavelengths keep WDM data safe [OK]

Common Mistakes:

• Trying to merge all streams on one wavelength
• Thinking power increase fixes wavelength failure
• Assuming switching multiplexing types is easy