Login
OR
Don't worry. We'll fix this for you!
Imagine you have a single telephone line but multiple people want to make calls at the same time. How can all these conversations happen simultaneously without interference? The answer lies in a technique called multiplexing. Multiplexing is a fundamental concept in computer networks and telecommunications that allows multiple signals or data streams to share a single communication channel efficiently.
Communication channels, such as cables or wireless frequencies, have limited capacity or bandwidth. If each user or device had to use a separate channel, the cost and complexity would skyrocket. Multiplexing solves this problem by combining multiple signals into one channel, making the best use of available resources.
Think of multiplexing as a way to organize traffic on a busy road. Instead of building many separate roads for each vehicle, we create lanes or time schedules so that many vehicles can use the same road without crashing into each other.
At its core, multiplexing involves two main processes:
This process requires special devices called multiplexers (MUX) and demultiplexers (DEMUX).
Imagine a multi-lane highway where each lane carries cars (signals) moving side by side. This is similar to Frequency Division Multiplexing. Alternatively, think of a single-lane toll booth where cars pass one at a time in a timed sequence - this resembles Time Division Multiplexing. For fiber optics, imagine different colors of light traveling together in one cable, each carrying separate data - this is like Wavelength Division Multiplexing.
In Frequency Division Multiplexing (FDM), the total available bandwidth of a communication channel is divided into non-overlapping frequency bands. Each band carries a separate signal simultaneously. This is like tuning into different radio stations, each broadcasting at a unique frequency.
To avoid interference between adjacent frequency bands, small gaps called guard bands are placed between them. These guard bands act as buffers to prevent signal overlap.
Key Points:
Time Division Multiplexing (TDM) divides the time on a single communication channel into fixed intervals called time slots. Each channel is assigned a specific time slot during which it can transmit its data. The process repeats cyclically, allowing multiple signals to share the same frequency channel but at different times.
There are two types of TDM:
Key Points:
Wavelength Division Multiplexing (WDM) is used primarily in fiber optic communication. Instead of radio frequencies, WDM uses different wavelengths (colors) of light to carry separate data streams simultaneously through a single optical fiber.
This technique allows enormous data capacity since multiple wavelengths can coexist without interference, similar to how a prism splits white light into multiple colors.
Key Points:
Multiplexing is everywhere in modern communication:
Advantages:
Limitations:
Demultiplexing: The reverse process of multiplexing, separating combined signals back into individual channels.
Multiplexer and Demultiplexer Devices: Hardware that performs multiplexing and demultiplexing functions.
Comparison with Other Network Concepts: Multiplexing differs from switching and routing, as it focuses on sharing a single channel rather than directing data paths.
Step 1: Identify the number of channels \( n = 5 \).
Step 2: Each channel bandwidth \( B_i = 4 \) MHz.
Step 3: Guard band \( B_{guard} = 0.5 \) MHz.
Step 4: Apply the formula for total bandwidth:
\[ B_{total} = \sum_{i=1}^{5} 4 + (5-1) \times 0.5 = 5 \times 4 + 4 \times 0.5 = 20 + 2 = 22 \text{ MHz} \]
Answer: The total bandwidth required is 22 MHz.
Step 1: Number of channels \( n = 8 \).
Step 2: Frame duration \( T_{frame} = 2 \) ms.
Step 3: Use the formula for time slot duration:
\[ T_{slot} = \frac{T_{frame}}{n} = \frac{2 \text{ ms}}{8} = 0.25 \text{ ms} \]
Answer: Each time slot duration is 0.25 ms.
Step 1: Number of channels \( n = 10 \).
Step 2: Cost per multiplexer = Rs.15,000.
Step 3: Cost per demultiplexer = Rs.12,000.
Step 4: Total cost = Cost of MUX + Cost of DEMUX.
Assuming one multiplexer and one demultiplexer handle all channels:
Total cost = Rs.15,000 + Rs.12,000 = Rs.27,000.
Answer: The total cost for multiplexing equipment is Rs.27,000.
Step 1: For FDM:
Number of channels \( n = 4 \), bandwidth per channel \( B_i = 3 \) MHz, guard band \( B_{guard} = 0.2 \) MHz.
Total bandwidth:
\[ B_{total} = 4 \times 3 + (4 - 1) \times 0.2 = 12 + 0.6 = 12.6 \text{ MHz} \]
Step 2: For TDM:
Each channel data rate = 3 Mbps, number of channels = 4.
Total data rate:
\[ R_{total} = 4 \times 3 = 12 \text{ Mbps} \]
Answer:
Note: Bandwidth in MHz and data rate in Mbps are related but not directly comparable without modulation details. TDM can be more bandwidth-efficient by sharing the channel in time.
Step 1: Number of wavelengths \( n = 16 \).
Step 2: Capacity per wavelength \( C_{wavelength} = 10 \) Gbps.
Step 3: Use the formula for total capacity:
\[ C_{total} = n \times C_{wavelength} = 16 \times 10 = 160 \text{ Gbps} \]
Answer: The total data capacity of the fiber optic cable is 160 Gbps.
When to use: When calculating total bandwidth in FDM problems.
When to use: When solving time slot allocation questions.
When to use: When trying to recall multiplexing types quickly.
When to use: During numerical problems involving bandwidth, time, or data rates.
When to use: When visualizing or explaining WDM.
| Feature | FDM | TDM | WDM |
|---|---|---|---|
| Division Basis | Frequency bands | Time slots | Light wavelengths |
| Simultaneous Transmission | Yes | No (sequential) | Yes |
| Guard Bands/Slots | Guard bands needed | Time slots assigned | No guard bands, uses wavelengths |
| Typical Use | Radio, telephone | Digital data streams | Fiber optic communication |
| Bandwidth Efficiency | Lower due to guard bands | Higher, depends on slot usage | Very high, multiple wavelengths |
| Equipment Complexity | Moderate | Moderate | High, optical components |
Progress tracking is paywalled — subscribe to mark subtopics as understood and save your streak.
Go to practice →
Your Score
Your Rank
| Rank | Name | Score |
|---|
