23 Explain the significance of twisting the wires in twisted pair cable

Twisting the wires in a twisted pair cable is a crucial design feature that helps reduce
electromagnetic interference (EMI) and crosstalk. The primary significance of twisting the
wires includes:

1. Reduction of Crosstalk – Twisting minimizes interference between adjacent pairs of

wires by ensuring that the electromagnetic signals cancel each other out.

2. Minimization of Electromagnetic Interference (EMI) – Twisted pairs are less

susceptible to external interference from electrical devices and radio signals,
improving signal integrity.

3. Better Signal Transmission – The twisting helps maintain a balanced electrical signal,
ensuring reliable data transmission over long distances.

4. Improved Noise Immunity – The alternating twists reduce susceptibility to noise,

making the cable more efficient for data communication.

5. Compliance with Network Standards – Twisted pair cables conform to structured

cabling standards (like Ethernet) and provide cost-effective networking solutions.

24 Write in brief about unicast, multicast and broadcast communication network

1. Unicast Communication

o A one-to-one communication where data is sent from a single sender to a

single receiver.

o Example: Web browsing, emails, video streaming (YouTube, Netflix).

2. Multicast Communication

o A one-to-many communication where data is sent from one sender to

multiple specific receivers.

o Efficient for applications that require sending the same data to multiple
users.

o Example: Video conferencing, live streaming, IPTV.

3. Broadcast Communication

o A one-to-all communication where data is sent from a single sender to all

devices in a network.

o Used in scenarios where all devices need to receive the same message.

o Example: ARP (Address Resolution Protocol) requests, television

broadcasting.
25 Compare Unshielded Twisted Pair, (UTP) and Shielded Twisted Pair (STP) cables.

26 Explain light propagation in fiber.

Light propagates through an optical fiber based on the principle of total internal reflection
(TIR). The core of the fiber has a higher refractive index than the cladding, ensuring that light
signals remain confined within the core.

1. Step-Index Fiber:

o Light rays reflect in a zig-zag manner due to a sharp difference in refractive

indices.

o Used in multimode fibers for short-distance communication.

2. Graded-Index Fiber:

o The refractive index gradually decreases from the core to the cladding,
allowing smoother light propagation and reducing dispersion.

o Used for high-speed data transmission over longer distances.

3. Single-Mode Fiber:

o Uses a narrow core to allow a single path for light, reducing signal
degradation.

o Suitable for long-distance communication like internet backbone

27 Mention different frequency bands along with their applications.

28 Enlist and define wireless transmission media.

Wireless transmission media enables communication without physical cables by using

electromagnetic waves. The main types are:

1. Radio Waves

o Used for long-distance communication.

o Example: AM/FM radio, mobile phones, TV broadcasting.

2. Microwaves

o Used for high-speed data transmission over short and long distances.

o Example: Satellite communication, Wi-Fi, radar systems.

3. Infrared (IR)

o Used for short-range communication without obstacles.

o Example: Remote controls, wireless keyboards/mice.

4. Bluetooth

o Low-power wireless communication for close-range device connections.

o Example: Wireless headphones, smartwatches, IoT devices.

5. Wi-Fi (Wireless Fidelity)

o Provides high-speed internet over short distances using radio signals.

o Example: Home and office networks, public hotspots.

 6. Satellite Communication

o Uses satellites to provide global coverage.

o Example: GPS, satellite phones, weather monitoring.

Each wireless transmission medium is used based on the distance, speed, and application
requirements.

29 Explain the construction of Coaxial cable with suitable diagram.

A coaxial cable is a type of electrical cable consisting of a central conductor, an insulating

layer, a metallic shield, and an outer insulating cover. It is widely used for transmitting high-
frequency signals, such as in television broadcasting, internet connections, and
telecommunications.

Construction of Coaxial Cable:

1. Central Conductor:

o Made of copper or aluminum.

o Carries the electrical signal.

2. Dielectric Insulator:

o Surrounds the central conductor.

o Made of polyethylene or Teflon to maintain spacing and reduce signal loss.

3. Metallic Shield:

o A braided or solid layer of metal (typically aluminum or copper).

o Protects against external electromagnetic interference (EMI).

4. Outer Insulating Sheath:

o Made of plastic or rubber.

o Protects the cable from environmental damage.

30 Define the term multiplexing and spreading.

Multiplexing:

Multiplexing is a technique used to transmit multiple signals over a single communication

channel or medium. It increases the efficiency of data transmission and optimizes the use of
bandwidth. Types of multiplexing include:

• Frequency Division Multiplexing (FDM)

• Time Division Multiplexing (TDM)

• Wavelength Division Multiplexing (WDM)

• Code Division Multiplexing (CDM)

Spreading:
 Spreading is a technique used in wireless communication where the transmitted signal is
spread over a wider frequency band than required. This improves signal robustness and
security. Types of spreading techniques include:

• Direct Sequence Spread Spectrum (DSSS)

• Frequency Hopping Spread Spectrum (FHSS)

31 Explain Frequency Division multiplexing with suitable diagram

31. Frequency Division Multiplexing (FDM) with Diagram

Frequency Division Multiplexing (FDM) is a technique where multiple signals are transmitted
simultaneously over different frequency bands in a shared medium.

Working of FDM:

• The available bandwidth is divided into multiple non-overlapping frequency bands.

• Each user or signal is assigned a specific frequency range.

• Signals are transmitted simultaneously but at different frequencies.

• A bandpass filter at the receiver extracts the desired frequency.

Diagram of FDM:

markdown

CopyEdit

___________________________________________________

| | | | | | | |

| f1 | f2 | f3 | f4 | f5 | f6 | f7 |

|_______|_______|_______|_______|_______|_______|_______|

Time →

Each frequency band (f1, f2, f3, etc.) carries a separate signal.

32 Draw and explain propagation modes in optical fiber

Optical fiber transmits light signals using different propagation modes:

1. Single-Mode Propagation:

• Uses a narrow core (~8-10 µm in diameter).

• Allows only one path for light to travel.

• Used for long-distance communication (high-speed internet, telecommunication).

2. Multi-Mode Propagation:

• Uses a wider core (~50-62.5 µm in diameter).

• Allows multiple paths for light signals.

 • Used for short-distance communication.

Diagram of Optical Fiber Propagation:

pgsql

CopyEdit

|---------------------|

| Outer Cladding |

|---------------------|

| Core (Light) | ← Single-mode: Straight path

|---------------------|

|---------------------|

| Outer Cladding |

|---------------------|

| Core (Light) | ← Multi-mode: Multiple reflections

33 Explain ground wave, sky wave and line of sight propagation

1. Ground Wave Propagation:

• Used for frequencies up to 3 MHz (AM radio).

• Signal travels along the Earth's surface.

• Affected by terrain and conductivity of the ground.

2. Sky Wave Propagation:

• Used for frequencies between 3 MHz to 30 MHz (Shortwave radio, HF

communication).

• Signal is reflected by the ionosphere back to Earth.

• Enables long-distance communication without satellites.

3. Line-of-Sight (LOS) Propagation:

• Used for frequencies above 30 MHz (VHF, UHF, and microwave).

• Signal travels in a straight line.

• Used in satellite communication, TV, and cellular networks.

Diagram of Propagation Modes:

pgsql

CopyEdit
 Ionosphere

────────

/ \

Sky Wave / \ Sky Wave

/ \

/------------\

| Transmitter | → → → → Line-of-Sight Signal

\------------/

Ground Wave Propagation

These propagation techniques are used based on frequency range and application
requirements.

4o

34 Discuss the advantages of fiber optics as communication medium?

Fiber optic communication offers several advantages over traditional copper-based

transmission media:

1. High Bandwidth: Fiber optics provide higher data transmission capacity, supporting
higher bandwidth and faster speeds.

2. Low Attenuation: Optical fibers suffer minimal signal loss over long distances
compared to copper cables.

3. Immunity to Electromagnetic Interference (EMI): Since optical signals are light-

based, they are not affected by electromagnetic interference, ensuring stable
communication.

4. Security: Fiber optics do not emit electromagnetic signals, making them difficult to
tap or intercept, ensuring higher security.

5. Lightweight and Small Size: Optical fibers are thinner and lighter than copper cables,
making them easier to install and manage.

6. Long Distance Transmission: Optical signals can travel much longer distances without
the need for repeaters, reducing infrastructure costs.

7. Durability and Reliability: Fiber optics are resistant to environmental factors like
temperature variations and moisture.
35 Define the following terms (a) Bandwidth,(b) Latency (c ) Delay

(a) Bandwidth:
Bandwidth refers to the data transfer capacity of a network or communication channel,
measured in bits per second (bps). It determines how much data can be transmitted over a
given time.

(b) Latency:
Latency is the time delay between the transmission and reception of data, usually measured
in milliseconds (ms). Lower latency is desirable for real-time applications like video streaming
and online gaming.

(c) Delay:
Delay is the total time taken for data to travel from the sender to the receiver. It consists of
propagation delay, transmission delay, processing delay, and queuing delay.

36 Explain Frequency Hopping Spread Spectrum (FHSS) technique with suitable diagram

FHSS is a method of transmitting radio signals by rapidly switching the carrier frequency over
different channels within a given bandwidth.

Working Principle:

1. The data signal is divided into small packets.

2. The transmitter changes the frequency at regular intervals using a pre-determined

hopping sequence.

3. The receiver, synchronized with the same hopping pattern, decodes the message
correctly.

4. This technique helps in minimizing interference and improving security.

Diagram:
(A simple block diagram showing the frequency changes over time, with a transmitter and
receiver synchronized to the hopping pattern.)

Advantages:

• Resistance to interference and jamming

• Increased security due to rapid frequency changes

• Better coexistence with other signals in the same frequency range

37 Explain Direct sequence spread spectrum(DSSS) technique with suitable diagram

DSSS spreads the data signal over a wider frequency band by multiplying it with a pseudo-
random noise (PN) sequence.

Working Principle:

1. The original data signal is combined with a high-rate pseudo-random noise sequence.

2. This results in a wider frequency bandwidth.

3. At the receiver end, the same PN sequence is used to de-spread the signal and
recover the original data.

Diagram:
(A simple block diagram showing the spreading and de-spreading process using a PN
sequence.)

Advantages:

• Better noise immunity

• Resistance to signal interception and jamming

• Increased reliability in communication

38 Write in detail the classification of transmission media and depict with neat diagrams as
applicable.

Transmission media are classified into two types:

1. Guided Media (Wired Media):

o Twisted Pair Cable: Used in telephone lines and LANs.

o Coaxial Cable: Used in cable TV and broadband networks.

o Optical Fiber: High-speed, long-distance communication.

2. Unguided Media (Wireless Media):

o Radio Waves: Used in broadcasting, Wi-Fi, and mobile communication.

o Microwaves: Used in satellite communication and point-to-point links.

o Infrared Waves: Used in short-range communication like remote controls.

Diagrams: (Illustrating each transmission medium with basic structure and usage scenarios.)
39 Explain wavelength Division Multiplexing (WDM) and Time Division Multiplexing(TDM)

Wavelength Division Multiplexing (WDM):

• WDM is used in fiber optic communication, where multiple data signals of different
wavelengths (colors) are transmitted simultaneously over a single optical fiber.

• It increases bandwidth and efficiency.

Time Division Multiplexing (TDM):

• TDM divides time into slots and assigns each signal a specific time slot for
transmission.

• Two types: Synchronous TDM (fixed time slots) and Statistical TDM (variable time
slots).

Diagram: (Illustrating WDM with different wavelengths in fiber optics and TDM with time
slots assigned to different signals.)

40 Discuss the statistical multiplexing and synchronous time-division multiplexing with suitable
example.

1. Statistical Multiplexing:

o Dynamically allocates bandwidth based on demand.

o Efficient for bursty traffic like internet browsing.

o Example: Packet-switched networks like Ethernet.

2. Synchronous Time-Division Multiplexing (TDM):

o Fixed time slots are assigned to each user.

o Less efficient but predictable.

o Example: Traditional telephone networks.

Diagram: (Illustrating both methods with time slots vs. dynamic allocation.)
41 Compare 1G, 2G, 3G, 4G and 5G mobile communication systems.