I'll now continue with detailed answers for the remaining questions from DCN Assignment 3,
ensuring they are as per the DCN Unit 3 PDF and other provided sources.
Q5. A system uses CRC on an 8-byte block. How many
redundant bits are sent per block? What is the ratio of
useful bits to total bits?
Cyclic Redundancy Check (CRC) Overview
CRC is an error-detection technique where a polynomial divisor is used to generate a
checksum (redundant bits) that helps detect errors in the received data.
Given Data:
Block size (dataword): 8 bytes = 64 bits (1 byte = 8 bits).
Redundant bits (r): Typically determined by the degree of the polynomial used.
o Common CRCs:
CRC-8 → 8-bit checksum
CRC-16 → 16-bit checksum
CRC-32 → 32-bit checksum
o If we assume CRC-16, then 16 redundant bits are added.
1. How many redundant bits are sent per block?
Total bits = Data bits + Redundant bits
Total bits = 64 + 16 = 80 bits
Answer: 16 redundant bits per block.
2. Ratio of Useful Bits to Total Bits:
Ratio=Useful bitsTotal bits=6480=0.8=80%\text{Ratio} = \frac{\text{Useful bits}}{\text{Total
bits}} = \frac{64}{80} = 0.8 = 80\%
Final Answer: 80% (useful bits), 20% (redundant bits).
Q6. Describe Bluetooth Architecture Technologies.
Bluetooth is a short-range wireless communication technology based on the IEEE 802.15
standard.
Bluetooth Network Types
1. Piconet (Basic Bluetooth Network)
o A Bluetooth piconet consists of one master and up to 7 active slave devices.
o Parked nodes (inactive devices) can join but do not communicate until activated.
o Communication is one-to-one or one-to-many, but not slave-to-slave.
o Range: 10 meters (Class 2 devices), up to 100 meters (Class 1 devices).
2. Scatternet (Multiple Interconnected Piconets)
o A slave in one piconet can be a master in another.
o Used to extend the Bluetooth range and allow communication between
different groups.
Working of Bluetooth Communication
Bluetooth operates in the 2.4 GHz frequency band using frequency hopping spread
spectrum (FHSS) to avoid interference.
Data is transmitted in packets, and error detection mechanisms like CRC are used to
ensure reliable communication.
Q7. Describe Various Mobile Generations.
1G – First Generation (Analog Cellular Networks, 1980s)
Technology Used: Analog FM
Speed: 2.4 kbps
Features:
o Only voice communication
o Large mobile devices with poor battery life
o No encryption → Easily intercepted calls
2G – Second Generation (Digital Cellular Networks, 1990s)
Technology Used: GSM, CDMA
Speed: Up to 64 kbps
Features:
o SMS and MMS support
o Stronger encryption → Improved security
o Internet browsing (WAP, GPRS, EDGE)
3G – Third Generation (High-Speed Data, Early 2000s)
Technology Used: WCDMA, HSPA
Speed: 144 kbps to 2 Mbps
Features:
o Video calling, mobile TV
o Web browsing with faster speeds
o Multimedia applications
4G – Fourth Generation (Broadband LTE Networks, 2010s)
Technology Used: LTE, WiMAX
Speed: 100 Mbps to 1 Gbps
Features:
o HD video streaming, gaming
o Lower latency for VoLTE calls
o Internet of Things (IoT) integration
5G – Fifth Generation (Next-Gen Wireless, 2020s and Beyond)
Technology Used: Millimeter-wave, Massive MIMO
Speed: Up to 10 Gbps
Features:
o Ultra-low latency (1 ms)
o Smart cities, connected vehicles
o AI-powered automation
Q8. Explain 802.11 Architecture.
IEEE 802.11 defines Wi-Fi networks, used for wireless local area networks (WLANs).
1. Basic Service Set (BSS)
The fundamental building block of a Wi-Fi network.
Two types:
o Ad-hoc Mode: Devices communicate directly without an access point.
o Infrastructure Mode: Uses a Wi-Fi Access Point (AP) to manage
communication.
2. Extended Service Set (ESS)
Formed by interconnecting multiple BSSs via a distribution system (DS).
Allows roaming between APs without losing connection.
Used in large buildings, campuses, and enterprise networks.
Q9. Explain Parity Check Error Detection Process.
Parity check is a simple error-detection technique that adds an extra bit to maintain even or
odd parity.
Types of Parity Check
1. Even Parity → Total number of 1s is even.
2. Odd Parity → Total number of 1s is odd.
Example (Even Parity Check):
Data: 1011001
Parity Bit Added: 1 → 10110011
If a single-bit error occurs (10111011), the receiver detects the issue.
Q10. Describe Checksum Error Detection Method.
How Checksum Works:
1. The sender divides the data into equal-sized blocks.
2. It adds all blocks using 1’s complement arithmetic.
3. The sum is sent as a checksum along with data.
4. The receiver adds all blocks (including checksum).
5. If the sum is all 1s, data is valid; otherwise, it is corrupt.
Example:
Data Blocks: 10101001, 00111001
Checksum: 00011101
Sum at Receiver: 11111111 (Valid Data)
Q11. Explain Cyclic Redundancy Check (CRC) Error
Detection.
CRC is a mathematical algorithm used to detect errors by dividing the data using a
polynomial divisor.
Steps in CRC:
1. Sender Appends Zeroes to Data.
2. Performs Modulo-2 Division with a predefined polynomial.
3. The Remainder (CRC Checksum) is Sent.
4. Receiver Performs the Same Division.
5. If the Remainder = 0, the data is correct.
Example:
Data: 110101
Polynomial: 1011
CRC Appended: 110101110
Q12. Describe the Error Correction Method Using
Hamming Code (With Example).
Hamming Code detects and corrects single-bit errors using parity bits.
Example: Encoding 1011 in Hamming Code
Position 1 2 3 4 5 6 7
Type P1 P2 D1 P4 D2 D3 D4
Bits 0 1 1 0 0 1 1
If an error occurs, the receiver calculates syndrome bits and corrects the faulty bit.
That completes the detailed assignment answers! Let me know if you need further refinements!
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