UPSC CSE Prelims
Internet and Communication Networks Previous Year Questions (PYQs)

Detailed Explanation:

Answer: Option 3 — 1, 3 and 4 only

Visible Light Communication (VLC) is an optical wireless communication technology that uses visible light spectrum for data transmission. Statements 1, 3, and 4 correctly describe VLC's characteristics, while statement 2 incorrectly classifies it as long-range communication.

✅ Statement 1 – Correct: VLC operates in the visible light spectrum range of 375 nm (violet) to 780 nm (red), which falls within the electromagnetic spectrum.

❌ Statement 2 – Incorrect: VLC is a short-range optical wireless communication technology, typically limited to distances within a room or line-of-sight areas, not long-range communication.

✅ Statement 3 – Correct: VLC can achieve data transmission speeds significantly faster than Bluetooth, with potential speeds reaching several Gbps compared to Bluetooth's maximum of around 50 Mbps.

✅ Statement 4 – Correct: Since VLC uses light waves instead of radio frequencies, it does not cause or suffer from electromagnetic interference (EMI), making it suitable for sensitive environments like hospitals and aircraft.

📝 Short Notes: Visible Light Communication (VLC)

• Technology Basis: Uses LED bulbs to transmit data through rapid light intensity modulation imperceptible to the human eye
• Spectrum Range: Operates in 375-780 nm wavelength (visible light spectrum)
• Speed: Can achieve data rates from 100 Mbps to several Gbps, much faster than WiFi and Bluetooth
• Range: Short-range technology, typically effective within 10 meters in line-of-sight conditions
• Advantages: No electromagnetic interference, high security (light cannot penetrate walls), energy efficient, uses existing LED infrastructure
• Limitations: Requires line-of-sight, affected by ambient light, cannot work through opaque objects
• Applications: Indoor navigation, underwater communication, secure data transfer in sensitive areas, vehicle-to-vehicle communication
• Li-Fi: A related technology that uses VLC for high-speed wireless internet connectivity

Detailed Explanation:

Answer: Option 4 — Neither 1 nor 2

Both statements about LTE and VoLTE technologies are incorrect. LTE is marketed as 4G (not 3G) and is a high-speed data technology that can also support voice through circuit-switched fallback, while VoLTE is not voice-only but enables voice calls over the same 4G LTE data network along with simultaneous data services.

❌ Statement 1 – Incorrect: LTE is commonly marketed as 4G technology, not 3G, and VoLTE is an enhancement of 4G LTE for voice services, not advanced 3G.
❌ Statement 2 – Incorrect: LTE is not data-only (it can support voice through fallback mechanisms), and VoLTE is not voice-only (it delivers voice over the data network while allowing simultaneous data usage).

📝 Short Notes: LTE and VoLTE Technologies

Detailed Explanation:

Answer: Option 3 — Both 1 and 2

✅ Statement 1 – Correct: LiFi (Light Fidelity) uses visible light waves from LED bulbs for high-speed data transmission through rapid flickering invisible to human eyes.

✅ Statement 2 – Correct: LiFi is a wireless technology with theoretical speeds exceeding 100 Gbps, significantly faster than WiFi's current maximum of 11 Gbps.

Detailed Explanation:

Project Loon was a Google initiative that used high-altitude balloons in the stratosphere to provide internet connectivity to remote and underserved areas, functioning as floating cell towers.

The project was discontinued in January 2021 due to commercial viability challenges, despite its technological success in delivering wireless internet access.

Detailed Explanation:

✅ Statement 1 – Correct: NFC (Near Field Communication) is a contactless communication technology that uses electromagnetic radio fields operating at 13.56 MHz frequency to enable data exchange between devices.

❌ Statement 2 – Incorrect: NFC is designed for very short-range communication, typically requiring devices to be within 4-10 cm (a few centimeters) of each other, not a metre. This short range is a deliberate security feature.

✅ Statement 3 – Correct: NFC supports encryption protocols and secure elements to protect sensitive data during transmission, making it suitable for contactless payments and secure access control applications.