Computer Networks & Data Communication (4361101) - Summer 2024 Solution

Question 1(a) [3 marks]

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List the different Network Topologies and discuss any one in detail.

Answer:

Star Topology Details:

• Central Hub: All nodes connect to one central device
• Point-to-Point: Each connection is dedicated between node and hub
• Easy Management: Simple to install and troubleshoot

Mnemonic: “STAR = Single Terminal All Reach”

Question 1(b) [4 marks]

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Explain how point-to-point and broadcast transmission technologies are used in modern communication systems with examples of real-world applications and discuss their advantages and limitations.

Answer:

Point-to-Point Applications:

• Dedicated Lines: Leased lines between offices
• Satellite Links: Ground station to satellite communication
• Cable Modems: Home to ISP connection

Broadcast Applications:

• WiFi Networks: Router broadcasts to multiple devices
• Television: One transmitter to many receivers

Mnemonic: “P2P = Private Path, Broadcast = Big Audience”

Question 1(c) [7 marks]

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Describe OSI model with function of all layers.

Answer:

graph TD
    A[Application Layer 7] --> B[Presentation Layer 6]
    B --> C[Session Layer 5]
    C --> D[Transport Layer 4]
    D --> E[Network Layer 3]
    E --> F[Data Link Layer 2]
    F --> G[Physical Layer 1]

Key Functions:

• Upper Layers (5-7): Handle application-related services
• Lower Layers (1-4): Handle data transmission and routing
• Encapsulation: Each layer adds its own header

Mnemonic: “All People Seem To Need Data Processing”

Question 1(c OR) [7 marks]

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Write a functional description of all layer of TCP/IP model.

Answer:

graph TD
    A[Application Layer] --> B[Transport Layer]
    B --> C[Internet Layer]
    C --> D[Network Access Layer]

Layer Functions:

• Application: Provides network services to applications
• Transport: Ensures reliable or unreliable delivery
• Internet: Routes packets across networks using IP addresses
• Network Access: Handles physical transmission media

Mnemonic: “Applications Transport Internet Networks”

Question 2(a) [3 marks]

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Describe Function of firewall in network security.

Answer:

Firewall Functions:

• Packet Filtering: Controls incoming and outgoing network traffic
• Access Control: Blocks unauthorized access attempts
• Traffic Monitoring: Logs and analyzes network activity

Types:

• Hardware Firewall: Physical device protecting entire network
• Software Firewall: Program installed on individual computers
• Stateful Inspection: Tracks connection states and contexts

Mnemonic: “Firewall = Filter, Access, Monitor”

Question 2(b) [4 marks]

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Compare FDDI (Fiber Distributed Data Interface) and CDDI (Copper Distributed Data Interface) in terms of their key characteristics, advantages, and applications.

Answer:

FDDI Advantages:

• Long Distance: Supports campus-wide networks
• High Security: Immune to electromagnetic interference
• Reliability: Better error detection and recovery

CDDI Advantages:

• Cost Effective: Uses existing copper infrastructure
• Easy Installation: Standard twisted pair cabling
• Compatibility: Works with existing network equipment

Mnemonic: “FDDI = Fiber Distance, CDDI = Copper Cost”

Question 2(c) [7 marks]

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Explain and distinguish Ethernet, Fast Ethernet, Gigabit Ethernet.

Answer:

graph LR
    A[Ethernet 10 Mbps] --> B[Fast Ethernet 100 Mbps]
    B --> C[Gigabit Ethernet 1000 Mbps]

Key Differences:

• Speed Evolution: 10x increase at each generation
• Media Support: From coax to twisted pair to fiber
• Applications: LAN backbone, server connections, desktop
• Backward Compatibility: Newer standards support older devices

Standards:

• 10Base-T: 10 Mbps over twisted pair
• 100Base-TX: 100 Mbps over Category 5 UTP
• 1000Base-T: 1 Gbps over Category 5e/6 UTP

Mnemonic: “Every Fast Gigabit = 10, 100, 1000”

Question 2(a OR) [3 marks]

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Explain its role and function of router within a network infrastructure.

Answer:

Router Functions:

• Packet Forwarding: Routes data packets between different networks
• Path Determination: Selects best route using routing tables
• Network Isolation: Separates broadcast domains

Key Roles:

• Inter-network Communication: Connects LANs to WANs
• Traffic Management: Controls data flow between networks
• Protocol Translation: Converts between different network protocols

Mnemonic: “Router = Route, Isolate, Connect”

Question 2(b OR) [4 marks]

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Explain the structure of FDDI (Fiber Distributed Data Interface) and give its advantages.

Answer:

FDDI Structure:

Components:

• Dual Ring: Primary and secondary rings for redundancy
• Token Passing: Uses token for media access control
• Concentrators: Connect multiple stations to ring

Advantages:

• High Reliability: Dual ring provides fault tolerance
• Fast Speed: 100 Mbps data transmission rate
• Long Distance: Supports up to 200 km ring circumference
• Self-Healing: Automatic reconfiguration when link fails

Mnemonic: “FDDI = Fast, Dual, Distance, Immune”

Question 2(c OR) [7 marks]

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Explain roll of network Devices. Describe in brief about all the devices.

Answer:

graph TD
    A[Physical Layer] --> B[Repeater, Hub]
    C[Data Link Layer] --> D[Bridge, Switch]
    E[Network Layer] --> F[Router]
    G[All Layers] --> H[Gateway]

Device Functions:

• Repeater: Amplifies and regenerates signals
• Hub: Simple connection point for multiple devices
• Bridge: Intelligent forwarding based on MAC addresses
• Switch: High-performance bridge with multiple ports
• Router: Intelligent path selection between networks
• Gateway: Complete protocol stack conversion

Mnemonic: “Repeat, Hub, Bridge, Switch, Route, Gateway”

Question 3(a) [3 marks]

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Name any three data link layer protocol and explain any one in detail.

Answer:

Data Link Layer Protocols:

• HDLC (High-Level Data Link Control)
• PPP (Point-to-Point Protocol)
• Ethernet (IEEE 802.3)

HDLC Protocol Details:

• Frame Structure: Flag, Address, Control, Data, FCS, Flag
• Error Detection: Frame Check Sequence (FCS)
• Flow Control: Sliding window mechanism

HDLC Frame Format:

Mnemonic: “HDLC = High Data Link Control”

Question 3(b) [4 marks]

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Explain error control and flow control at data link layer

Answer:

Error Control Methods:

• Detection: CRC, Checksum identify errors
• Correction: ARQ (Automatic Repeat Request)
• Prevention: Forward Error Correction (FEC)

Flow Control Methods:

• Stop-and-Wait: Send one frame, wait for ACK
• Sliding Window: Send multiple frames before ACK
• Buffer Management: Prevent receiver overflow

Mnemonic: “Error = Detect, Flow = Control”

Question 3(c) [7 marks]

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Compare IPv6 and IPv4.

Answer:

IPv4 Example: 192.168.1.100 IPv6 Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334

Key Differences:

• Address Exhaustion: IPv4 addresses nearly exhausted
• Header Efficiency: IPv6 simplified header structure
• Security: IPv6 has built-in security features
• Quality of Service: Better QoS support in IPv6

Mnemonic: “IPv6 = Infinite, Integrated, Improved”

Question 3(a OR) [3 marks]

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Explain the differences between guided and unguided transmission media used in computer networks

Answer:

Guided Media:

• Twisted Pair: Telephone lines, LANs
• Coaxial Cable: Cable TV, older networks
• Fiber Optic: High-speed, long-distance

Unguided Media:

• Radio Waves: WiFi, Bluetooth
• Microwaves: Point-to-point links
• Infrared: Short-range communication

Mnemonic: “Guided = Ground, Unguided = Air”

Question 3(b OR) [4 marks]

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Describe circuit switching and packet switching.

Answer:

Circuit Switching:

• Setup Phase: Establishes dedicated connection
• Data Transfer: Continuous transmission
• Teardown: Releases connection resources

Packet Switching:

• Store-and-Forward: Packets stored at intermediate nodes
• Dynamic Routing: Each packet routed independently
• Resource Sharing: Bandwidth shared among users

Mnemonic: “Circuit = Continuous, Packet = Pieces”

Question 3(c OR) [7 marks]

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Explain IPv4 OR IPv6 in detail.

Answer (IPv4):

IPv4 Address Structure:

• 32-bit Address: Divided into 4 octets
• Dotted Decimal: 192.168.1.1 format
• Network + Host: Address split into network and host portions

Special Addresses:

• Loopback: 127.0.0.1 (local host)
• Private: 192.168.x.x, 10.x.x.x, 172.16-31.x.x
• Broadcast: 255.255.255.255

Subnetting:

• Subnet Mask: Identifies network portion
• CIDR: Classless Inter-Domain Routing
• Variable Length: Different subnet sizes

IPv4 Header:

Mnemonic: “IPv4 = 4 octets, 32 bits, Classes A-C”

Question 4(a) [3 marks]

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Give full name of ARP and RARP and describe them.

Answer:

Full Names:

• ARP: Address Resolution Protocol
• RARP: Reverse Address Resolution Protocol

ARP Process:

• Request: “Who has IP 192.168.1.1?”
• Reply: “192.168.1.1 is at MAC 00:1A:2B:3C:4D:5E”
• Cache: Stores mappings for future use

RARP Process:

• Diskless Workstations: Get IP from server
• Broadcast Request: Sends MAC address
• Server Response: Returns assigned IP address

Mnemonic: “ARP = Address to MAC, RARP = Reverse”

Question 4(b) [4 marks]

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Describe DSL technology with its advantages and limitations.

Answer:

DSL (Digital Subscriber Line):

Advantages:

• Existing Infrastructure: Uses telephone lines
• Always-On: Continuous internet connection
• Voice + Data: Simultaneous phone and internet
• Cost-Effective: Affordable for home users

Limitations:

• Distance Dependent: Speed decreases with distance
• Upload Speed: Lower than download speed (ADSL)
• Line Quality: Affected by copper wire condition
• Availability: Not available in all areas

Mnemonic: “DSL = Digital Subscriber Line”

Question 4(c) [7 marks]

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Role of DNS- Domain Name System.

Answer:

DNS Functions:

• Name Resolution: Converts domain names to IP addresses
• Hierarchical Structure: Organized in tree-like structure
• Distributed Database: Information stored across multiple servers

graph TD
    A[Root Servers] --> B[Top Level Domain .com]
    A --> C[Top Level Domain .org]
    B --> D[google.com]
    B --> E[yahoo.com]
    D --> F[www.google.com]
    D --> G[mail.google.com]

DNS Hierarchy:

• Root Domain: Highest level (.)
• Top-Level Domain: .com, .org, .net, .edu
• Second-Level Domain: google.com, yahoo.com
• Subdomain: www.google.com, mail.google.com

DNS Resolution Process:

1. Client Query: User types www.example.com
2. Local DNS: Checks local cache
3. Root Server: Queries root DNS server
4. TLD Server: Queries .com server
5. Authoritative Server: Gets IP address
6. Response: Returns IP to client

DNS Record Types:

• A Record: Maps domain to IPv4 address
• AAAA Record: Maps domain to IPv6 address
• CNAME: Canonical name (alias)
• MX: Mail exchange server
• NS: Name server records

Mnemonic: “DNS = Domain Name System”

Question 4(a OR) [3 marks]

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Give full name of DHCP and BOOTP. and describe them.

Answer:

Full Names:

• DHCP: Dynamic Host Configuration Protocol
• BOOTP: Bootstrap Protocol

DHCP Process:

• Discover: Client broadcasts request
• Offer: Server offers IP address
• Request: Client requests specific IP
• Acknowledge: Server confirms assignment

BOOTP Process:

• Static Configuration: Pre-configured IP assignments
• Diskless Boot: Workstations boot from network
• Server Response: Provides IP and boot information

Mnemonic: “DHCP = Dynamic, BOOTP = Bootstrap”

Question 4(b OR) [4 marks]

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Differences Between Virtual Circuits and Datagram Networks.

Answer:

Virtual Circuits:

• Path Establishment: Creates virtual connection
• State Information: Maintains connection state
• Examples: ATM, Frame Relay

Datagram Networks:

• Independent Packets: Each packet routed separately
• Stateless: No connection state maintained
• Examples: Internet Protocol (IP)

Mnemonic: “Virtual = Connection, Datagram = Independent”

Question 4(c OR) [7 marks]

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Explain TCP and UDP protocol in transport layer

Answer:

TCP (Transmission Control Protocol):

• Three-Way Handshake: SYN, SYN-ACK, ACK
• Flow Control: Sliding window mechanism
• Error Recovery: Retransmission of lost packets
• Congestion Control: Prevents network overload

TCP Header:

UDP (User Datagram Protocol):

• Simple Protocol: Minimal overhead
• Best Effort: No guarantee of delivery
• Applications: DNS, DHCP, streaming media
• Real-time Communication: Voice, video applications

UDP Header:

Applications:

• TCP: Web browsing, email, file transfer
• UDP: Online gaming, video streaming, DNS queries

Mnemonic: “TCP = Reliable, UDP = Fast”

Question 5(a) [3 marks]

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Explain any two of following. (1) WWW (2) FTP (3) SMTP

Answer:

WWW (World Wide Web):

• HTTP Protocol: HyperText Transfer Protocol
• Web Browser: Client software (Chrome, Firefox)
• Web Server: Serves web pages (Apache, IIS)

FTP (File Transfer Protocol):

• File Transfer: Upload and download files
• Two Modes: Active and passive mode
• Authentication: Username and password required

Mnemonic: “WWW = Web, FTP = Files”

Question 5(b) [4 marks]

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Difference between symmetric and asymmetric encryption algorithms.

Answer:

Symmetric Encryption:

• Single Key: Same key used by sender and receiver
• Key Management: Secure key distribution required
• Performance: Fast encryption/decryption
• Applications: Bulk data encryption

Asymmetric Encryption:

• Key Pair: Public key for encryption, private key for decryption
• Key Distribution: Public key can be shared openly
• Performance: Slower than symmetric
• Applications: Digital signatures, key exchange

Mnemonic: “Symmetric = Same, Asymmetric = Different”

Question 5(c) [7 marks]

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Define the terms “encryption” and “decryption” in the context of cryptography.

Answer:

Encryption:

• Definition: Process of converting plaintext into ciphertext
• Purpose: Protect data confidentiality
• Input: Plaintext + Key
• Output: Ciphertext

Decryption:

• Definition: Process of converting ciphertext back to plaintext
• Purpose: Retrieve original data
• Input: Ciphertext + Key
• Output: Plaintext

graph LR
    A[Plaintext] --> B[Encryption]
    B --> C[Ciphertext]
    C --> D[Decryption]
    D --> E[Plaintext]
    F[Key] --> B
    G[Key] --> D

Cryptographic Process:

1. Sender: Encrypts message using key
2. Transmission: Sends ciphertext over network
3. Receiver: Decrypts ciphertext using key
4. Recovery: Gets original plaintext message

Types of Encryption:

• Stream Cipher: Encrypts one bit/byte at a time
• Block Cipher: Encrypts fixed-size blocks
• Hash Function: One-way encryption (no decryption)

Applications:

• Data Protection: Secure file storage
• Communication: Secure messaging
• Authentication: Digital signatures
• Privacy: Personal information protection

Security Requirements:

• Confidentiality: Only authorized users can read
• Integrity: Data hasn’t been tampered with
• Authentication: Verify sender identity
• Non-repudiation: Sender cannot deny sending

Mnemonic: “Encryption = Hide, Decryption = Reveal”

Question 5(a OR) [3 marks]

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Difference between IMAP and POP3

Answer:

IMAP (Internet Message Access Protocol):

• Server Storage: Messages remain on server
• Multi-Device: Access from multiple devices
• Synchronization: Changes sync across devices

POP3 (Post Office Protocol 3):

• Download: Messages downloaded to client
• Single Device: Best for one device access
• Storage: Client manages message storage

Mnemonic: “IMAP = Internet Access, POP3 = Post Office”

Question 5(b OR) [4 marks]

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Briefly describe the Information Technology (Amendment) Act, 2008, and its impact on cyber laws in India.

Answer:

IT Act 2008 Key Features:

• Cyber Crimes: Defines various cyber offenses
• Data Protection: Privacy and security requirements
• Digital Signatures: Legal recognition of e-signatures
• Penalties: Fines and imprisonment for violations

Major Amendments:

• Section 66A: Criminalized offensive messages (later struck down)
• Section 69: Government power to intercept information
• Section 72A: Punishment for disclosure of personal information
• Section 43A: Compensation for data breach

Impact on Cyber Laws:

• Legal Framework: Comprehensive cyber law structure
• Business Compliance: Data protection requirements
• Individual Rights: Privacy protection mechanisms
• Law Enforcement: Tools for investigating cyber crimes

Mnemonic: “IT Act = Internet Technology Act”

Question 5(c OR) [7 marks]

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Difference between symmetric and asymmetric encryption algorithms.

Answer:

Symmetric Encryption Details:

• Algorithm Types: Stream ciphers, Block ciphers
• Key Distribution Problem: Secure channel needed for key exchange
• Applications: Bulk data encryption, VPNs, file encryption
• Advantages: Fast, efficient for large amounts of data
• Disadvantages: Key management complexity, no digital signatures

Asymmetric Encryption Details:

• Public Key Infrastructure: PKI for key management
• Digital Signatures: Authentication and non-repudiation
• Applications: Email security, SSL/TLS, digital certificates
• Advantages: Secure key exchange, digital signatures
• Disadvantages: Computationally intensive, slower processing

Hybrid Approach:

• Best of Both: Combines symmetric and asymmetric encryption
• Key Exchange: Asymmetric for key distribution
• Data Encryption: Symmetric for actual data
• Example: SSL/TLS uses both methods

graph TD
    A[Encryption Methods] --> B[Symmetric]
    A --> C[Asymmetric]
    B --> D[Same Key]
    B --> E[Fast Processing]
    C --> F[Key Pair]
    C --> G[Slow Processing]

Real-world Applications:

• Banking: ATM transactions use symmetric encryption
• E-commerce: HTTPS uses hybrid encryption
• Email: PGP uses asymmetric for key exchange
• Mobile: WhatsApp uses end-to-end encryption

Security Considerations:

• Key Length: Longer keys provide better security
• Algorithm Strength: Choose proven algorithms
• Implementation: Proper coding prevents vulnerabilities
• Key Storage: Secure key management essential

Performance Comparison:

Future Trends:

• Quantum Computing: Threat to current asymmetric algorithms
• Post-Quantum Cryptography: New algorithms being developed
• Elliptic Curve: More efficient asymmetric encryption
• Lightweight Cryptography: For IoT devices

Mnemonic: “Symmetric = Same Speed, Asymmetric = Advanced Security”