Question 1(a) [3 marks]

Explain NAND logic gate.

Answer:

NAND gate is a universal logic gate that produces output 0 only when all inputs are 1.

Truth Table:

A	B	Y = A NAND B
0	0	1
0	1	1
1	0	1
1	1	0

Symbol:

    A ----+---D>o--- Y
          |   |
    B ----+   |
              |

NAND Function: Output is complement of AND operation
Universal Gate: Can implement any logic function
Low Power: Requires fewer transistors in IC design

Mnemonic: "NOT AND = NAND"

Question 1(b) [4 marks]

Draw AND logic Gate using NOR Gate only.

Answer:

AND gate can be implemented using NOR gates by applying De Morgan's theorem.

Circuit Diagram:

graph LR
    A[A] --> N1[NOR]
    A --> N1
    B[B] --> N2[NOR]
    B --> N2
    N1 --> N3[NOR]
    N2 --> N3
    N3 --> Y[Y = A.B]

Implementation Steps:

Step 1: Create NOT A using NOR gate (A NOR A = A')
Step 2: Create NOT B using NOR gate (B NOR B = B')
Step 3: Apply De Morgan's: A.B = (A' + B')'
Final Output: A AND B

Mnemonic: "Double inversion gives original function"

Question 1(c) [7 marks]

Explain components of Information System with diagram.

Answer:

Information System consists of five key components working together to process data into useful information.

System Diagram:

graph TB
    subgraph "Information System"
        H[Hardware]
        S[Software]
        D[Data]
        P[Procedures]
        Pe[People]
        
        H --> P
        S --> P
        D --> P
        Pe --> P
        P --> H
    end
    
    Input[Input] --> H
    H --> Output[Output]

Components:

Component	Description	Examples
Hardware	Physical devices	CPU, Memory, Keyboards
Software	Programs and applications	OS, Applications, Utilities
Data	Raw facts and figures	Numbers, Text, Images
Procedures	Rules and instructions	User manuals, SOPs
People	Users and operators	End users, IT staff

Input Processing: Data enters through hardware
Storage Management: Data stored and retrieved efficiently
Output Generation: Information presented to users
Integration: All components work cohesively

Mnemonic: "Hardware Supports Data Processing People"

Question 1(c OR) [7 marks]

Explain the working of Google Search Engine with example.

Answer:

Google Search Engine uses complex algorithms to find and rank web pages based on user queries.

Working Process:

sequenceDiagram
    participant U as User
    participant G as Google
    participant I as Index
    participant W as Web Pages
    
    U->>G: Enter Search Query
    G->>I: Query Processing
    I->>G: Retrieve Relevant Pages
    G->>G: Rank Pages (PageRank)
    G->>U: Display Results

Key Components:

Stage	Process	Example
Crawling	Discover web pages	Googlebot visits websites
Indexing	Store page content	Keywords stored in database
Ranking	Order by relevance	PageRank algorithm
Serving	Display results	Search results page

Example Search Process:

Query: "Introduction to IT Systems"
Processing: Parse keywords, check index
Ranking: Educational sites ranked higher
Results: GTU syllabus, tutorials, courses
PageRank Algorithm: Links determine page importance
Machine Learning: Improves search accuracy over time
Real-time Updates: Fresh content prioritized

Mnemonic: "Crawl Index Rank Serve"

Question 2(a) [3 marks]

Convert (16.75)10= ( )8

Answer:

Converting decimal 16.75 to octal requires separate conversion of integer and fractional parts.

Integer Part Conversion (16):

Division	Quotient	Remainder
16 ÷ 8	2	0
2 ÷ 8	0	2

Fractional Part Conversion (0.75):

Multiplication	Integer Part
0.75 × 8 = 6.0	6

Final Answer: (16.75)10 = (20.6)8

Verification: 2×8¹ + 0×8⁰ + 6×8⁻¹ = 16 + 0 + 0.75 = 16.75 ✓

Mnemonic: "Divide integer, Multiply fraction"

Question 2(b) [4 marks]

Explain Multiprocessing Operating System.

Answer:

Multiprocessing OS manages multiple processors working simultaneously to execute processes.

Architecture Diagram:

graph TB
    subgraph "Multiprocessing System"
        CPU1[CPU 1]
        CPU2[CPU 2]
        CPU3[CPU 3]
        SM[Shared Memory]
        OS[Operating System]
        
        CPU1 --> SM
        CPU2 --> SM
        CPU3 --> SM
        OS --> CPU1
        OS --> CPU2
        OS --> CPU3
    end

Key Features:

Feature	Description	Benefit
Parallel Processing	Multiple CPUs work together	Faster execution
Load Balancing	Tasks distributed evenly	Optimal resource usage
Fault Tolerance	System continues if one CPU fails	Higher reliability
Shared Resources	Common memory and I/O devices	Cost effective

Symmetric Multiprocessing: All processors have equal access
Process Synchronization: Coordinates between processors
Enhanced Performance: Linear speedup with processor count

Mnemonic: "Multiple Processors Process Parallel"

Question 2(c) [7 marks]

Define Operating System. List out and Explain the functions of Operating System.

Answer:

Definition: Operating System is system software that manages computer hardware and provides services to application programs.

Core Functions:

mindmap
  root((Operating System))
    Process Management
      Process Creation
      Scheduling
      Synchronization
    Memory Management
      Allocation
      Virtual Memory
      Paging
    File Management
      File Operations
      Directory Structure
      Access Control
    I/O Management
      Device Drivers
      Buffering
      Spooling

Detailed Functions:

Function	Description	Examples
Process Management	Controls program execution	Task scheduling, multitasking
Memory Management	Allocates RAM efficiently	Virtual memory, paging
File Management	Organizes data storage	File systems, directories
I/O Management	Controls input/output devices	Printer spooling, disk access
Security	Protects system resources	User authentication, access control

Resource Allocation: Distributes CPU time and memory
User Interface: Provides command line or GUI interaction
Error Handling: Manages system failures gracefully
System Calls: Interface between applications and hardware

Mnemonic: "Process Memory Files Input-Output Security"

Question 2(a OR) [3 marks]

Convert (1111111.11)2= ( )10

Answer:

Converting binary to decimal using positional notation method.

Conversion Table:

Position	Bit	Power	Value
6	1	2⁶	64
5	1	2⁵	32
4	1	2⁴	16
3	1	2³	8
2	1	2²	4
1	1	2¹	2
0	1	2⁰	1
-1	1	2⁻¹	0.5
-2	1	2⁻²	0.25

Calculation: 64 + 32 + 16 + 8 + 4 + 2 + 1 + 0.5 + 0.25 = 127.75

Final Answer: (1111111.11)2 = (127.75)10

Mnemonic: "Powers of Two add Together"

Question 2(b OR) [4 marks]

Explain Batch Operating System.

Answer:

Batch OS processes jobs in groups without user interaction during execution.

Working Model:

graph LR
    subgraph "Batch Processing"
        J1[Job 1] --> Q[Job Queue]
        J2[Job 2] --> Q
        J3[Job 3] --> Q
        Q --> CPU[CPU Processing]
        CPU --> O[Output]
    end

Characteristics:

Feature	Description	Impact
No Interaction	Jobs run without user input	High throughput
Job Queue	Multiple jobs wait in sequence	Efficient processing
Automatic Scheduling	OS selects next job	Minimal overhead
Batch Processing	Similar jobs grouped together	Resource optimization

Advantages: High system utilization, cost effective
Disadvantages: No real-time interaction, debugging difficulty
Applications: Payroll processing, data backup systems

Mnemonic: "Batch Jobs Queue Automatically"

Question 2(c OR) [7 marks]

Explain Architecture and modes of Linux System with Diagram.

Answer:

Linux follows layered architecture with distinct user and kernel modes.

System Architecture:

graph TB
    subgraph "User Space"
        UA[User Applications]
        SL[System Libraries]
        SC[System Calls]
    end
    
    subgraph "Kernel Space"
        VFS[Virtual File System]
        PM[Process Management]
        MM[Memory Management]
        NM[Network Management]
        DM[Device Management]
    end
    
    HW[Hardware]
    
    UA --> SL
    SL --> SC
    SC --> VFS
    SC --> PM
    SC --> MM
    SC --> NM
    SC --> DM
    VFS --> HW
    PM --> HW
    MM --> HW
    NM --> HW
    DM --> HW

Operating Modes:

Mode	Description	Access Level
User Mode	Applications run here	Limited privileges
Kernel Mode	OS core functions	Full hardware access
System Call Interface	Communication bridge	Controlled transition

Key Components:

Shell: Command interpreter interface
Kernel: Core system management
File System: Hierarchical data organization
Device Drivers: Hardware abstraction layer
Security Model: Permission-based access control
Modularity: Loadable kernel modules for flexibility
Portability: Runs on multiple hardware platforms

Mnemonic: "Users call Kernel for Hardware"

Question 3(a) [3 marks]

Differentiate between Open-source Software and Proprietary Software.

Answer:

Comparison Table:

Aspect	Open-source Software	Proprietary Software
Source Code	Freely available	Closed and protected
Cost	Usually free	Commercial license required
Modification	Can be modified	Cannot be modified
Examples	Linux, Firefox, LibreOffice	Windows, MS Office, Photoshop
Support	Community-based	Vendor-provided
Licensing	GPL, MIT, Apache	EULA, Commercial

Key Differences:

Freedom: Open-source allows complete customization
Security: Open code enables community security reviews
Vendor Lock-in: Proprietary creates dependency on vendor

Mnemonic: "Open Shares, Proprietary Protects"

Question 3(b) [4 marks]

Explain Ethernet Cable.

Answer:

Ethernet cable is the standard wired networking medium for LAN connections.

Cable Types:

graph TD
    subgraph "Ethernet Cables"
        UTP[Unshielded Twisted Pair]
        STP[Shielded Twisted Pair]
        Coax[Coaxial Cable]
        Fiber[Fiber Optic]
    end
    
    UTP --> Cat5[Cat 5/5e/6/6a]
    Fiber --> SM[Single Mode]
    Fiber --> MM[Multi Mode]

Cable Specifications:

Type	Speed	Distance	Usage
Cat 5e	1 Gbps	100m	Basic networking
Cat 6	10 Gbps	55m	High-speed LAN
Cat 6a	10 Gbps	100m	Enterprise networks
Fiber Optic	100+ Gbps	40km+	Long-distance, high-speed

Connector Type: RJ-45 for twisted pair cables
Wiring Standards: T568A and T568B color codes
Applications: Internet connectivity, file sharing, VoIP

Mnemonic: "Twisted pairs Carry Digital Data"

Question 3(c) [7 marks]

Explain Time Division Multiplexing with diagram.

Answer:

TDM allows multiple signals to share single transmission medium by allocating time slots.

TDM Process:

gantt
    title Time Division Multiplexing
    dateFormat X
    axisFormat %s
    
    section Channel A
    Slot A1 :0, 1
    Slot A2 :4, 5
    Slot A3 :8, 9
    
    section Channel B
    Slot B1 :1, 2
    Slot B2 :5, 6
    Slot B3 :9, 10
    
    section Channel C
    Slot C1 :2, 3
    Slot C2 :6, 7
    Slot C3 :10, 11
    
    section Channel D
    Slot D1 :3, 4
    Slot D2 :7, 8
    Slot D3 :11, 12

System Components:

Component	Function	Purpose
Multiplexer	Combines input signals	Single transmission
Time Slots	Fixed duration intervals	Fair channel access
Demultiplexer	Separates combined signal	Original signal recovery
Synchronization	Maintains timing alignment	Error-free transmission

Types of TDM:

Synchronous TDM: Fixed time slots for each channel
Asynchronous TDM: Dynamic slot allocation based on demand
Statistical TDM: Optimizes bandwidth utilization
Advantages: Efficient bandwidth usage, digital compatibility
Applications: Telephone systems, digital TV broadcasting
Bandwidth Efficiency: Multiple channels share single link

Mnemonic: "Time Divides Multiple Signals"

Question 3(a OR) [3 marks]

Differentiate between Hard Real Time and Soft Real Time Operating System.

Answer:

Comparison Table:

Aspect	Hard Real Time	Soft Real Time
Deadline	Must be met absolutely	Preferred but flexible
Consequences	System failure if missed	Performance degradation
Examples	Aircraft control, Pacemaker	Video streaming, Gaming
Response Time	Guaranteed maximum	Best effort basis
Cost	High development cost	Moderate cost
Reliability	Critical system reliability	User experience focused

Key Characteristics:

Hard RT: Zero tolerance for deadline misses
Soft RT: Occasional delays acceptable
Applications: Safety-critical vs user-interactive systems

Mnemonic: "Hard requires Precision, Soft allows Flexibility"

Question 3(b OR) [4 marks]

Explain Transmission Modes.

Answer:

Transmission modes define direction of data flow between communicating devices.

Mode Types:

graph TD
    subgraph "Transmission Modes"
        S[Simplex]
        HD[Half Duplex]  
        FD[Full Duplex]
    end
    
    S --> One[One Direction Only]
    HD --> Alt[Alternate Directions]
    FD --> Both[Both Directions Simultaneously]

Detailed Comparison:

Mode	Data Flow	Examples	Applications
Simplex	One direction only	Radio, TV broadcast	Broadcasting systems
Half Duplex	Both directions, not simultaneous	Walkie-talkie, CB radio	Two-way radios
Full Duplex	Both directions simultaneously	Telephone, Ethernet	Modern communication

Bandwidth Efficiency: Full duplex maximizes channel utilization
Cost Factor: Simplex cheapest, full duplex most expensive
Use Cases: Choose based on application requirements

Mnemonic: "Simplex Single, Half switches, Full flows Both"

Question 3(c OR) [7 marks]

List out types of Analog Modulation. Explain Amplitude Modulation with diagram.

Answer:

Types of Analog Modulation:

Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)

Amplitude Modulation Process:

graph TB
    subgraph "AM Modulation"
        MS[Message Signal] --> M[Modulator]
        CS[Carrier Signal] --> M
        M --> AMS[AM Signal]
    end
    
    subgraph "Waveforms"
        MW[Message Wave - Low Frequency]
        CW[Carrier Wave - High Frequency]
        AMW[AM Wave - Modulated Output]
    end

AM Characteristics:

Parameter	Description	Typical Values
Carrier Frequency	High frequency base signal	550-1600 kHz (AM radio)
Message Frequency	Information signal	20 Hz - 20 kHz (audio)
Modulation Index	Depth of modulation	0 to 1 (0-100%)
Bandwidth	Frequency spectrum used	2 × Message frequency

Mathematical Expression:

AM Signal: s(t) = Ac[1 + m·cos(ωmt)]cos(ωct)
Where: Ac = carrier amplitude, m = modulation index

Applications:

Broadcasting: AM radio stations
Aviation: Air traffic control communication
Citizens Band: CB radio systems
Advantages: Simple implementation, low cost receivers
Disadvantages: Susceptible to noise, power inefficient

Mnemonic: "Amplitude Varies with Message"

Question 4(a) [3 marks]

Draw Diagram of FSK AND PSK.

Answer:

Frequency Shift Keying (FSK):

Binary Data:  1    0    1    1    0
             
FSK Signal:   ╭╲╱╲╱╲╱╲╱╮  ╭╱╲╱╲╱╲╱╮  ╭╲╱╲╱╲╱╲╱╮
             ╱           ╲╱         ╲╱           ╲
            ╱             ╲         ╱             ╲
           ╱               ╲_______╱               ╲
          
          f1 (High Freq)    f2 (Low Freq)    f1 (High Freq)

Phase Shift Keying (PSK):

Binary Data:  1      0      1      1      0
             
PSK Signal:   ╭─╲ ╱─╮   ╭╲ ╱╮   ╭─╲ ╱─╮   ╭─╲ ╱─╮   ╭╲ ╱╮
             ╱   ╲╱   ╲ ╱  ╲╱  ╲ ╱   ╲╱   ╲ ╱   ╲╱   ╲ ╱  ╲╱  ╲
            ╱         ╲╱        ╲╱         ╲╱         ╲╱        ╲
           
           0° Phase      180° Phase    0° Phase     0° Phase    180° Phase

Key Differences:

FSK: Different frequencies for 1 and 0
PSK: Different phases for 1 and 0

Mnemonic: "FSK changes Frequency, PSK changes Phase"

Question 4(b) [4 marks]

If number of links in mesh topology are 45 than find maximum number of required nodes.

Answer:

Formula for Mesh Topology: Number of links = n(n-1)/2

Where n = number of nodes

Given: Number of links = 45

Calculation: 45 = n(n-1)/2 90 = n(n-1) n² - n - 90 = 0

Solving Quadratic Equation: Using quadratic formula: n = [-b ± √(b² - 4ac)] / 2a

Where a=1, b=-1, c=-90

n = [1 ± √(1 + 360)] / 2 n = [1 ± √361] / 2
n = [1 ± 19] / 2

Solutions: n = (1 + 19)/2 = 10 or n = (1 - 19)/2 = -9

Answer: Maximum number of nodes = 10

Verification: 10(10-1)/2 = 10×9/2 = 45 ✓

Mnemonic: "n nodes need n(n-1)/2 links"

Question 4(c) [7 marks]

Explain OSI Model with diagram.

Answer:

OSI (Open Systems Interconnection) model defines seven layers for network communication.

OSI Layer Stack:

graph TB
    subgraph "OSI Model"
        L7[Layer 7: Application]
        L6[Layer 6: Presentation] 
        L5[Layer 5: Session]
        L4[Layer 4: Transport]
        L3[Layer 3: Network]
        L2[Layer 2: Data Link]
        L1[Layer 1: Physical]
    end
    
    L7 --> L6
    L6 --> L5
    L5 --> L4
    L4 --> L3
    L3 --> L2
    L2 --> L1

Layer Functions:

Layer	Name	Function	Protocols	Devices
7	Application	User interface	HTTP, FTP, SMTP	Gateways
6	Presentation	Data formatting	SSL, JPEG, MPEG	Gateways
5	Session	Connection management	NetBIOS, RPC	Gateways
4	Transport	End-to-end delivery	TCP, UDP	Gateways
3	Network	Routing	IP, ICMP	Routers
2	Data Link	Frame transmission	Ethernet, PPP	Switches
1	Physical	Bit transmission	Ethernet cables	Hubs, Repeaters

Data Flow Process:

Encapsulation: Data moves down layers, headers added
Transmission: Physical layer sends bits across medium
Decapsulation: Receiving end moves up layers, headers removed
Standardization: Enables interoperability between vendors
Modularity: Each layer has specific responsibilities
Troubleshooting: Isolates problems to specific layers

Mnemonic: "All People Seem To Need Data Processing"

Question 4(a OR) [3 marks]

Explain Classful IPv4 addressing scheme with example.

Answer:

IPv4 classful addressing divides IP space into predefined classes based on network size.

Class Structure:

Class	Range	Default Mask	Networks	Hosts per Network
A	1-126	/8 (255.0.0.0)	126	16,777,214
B	128-191	/16 (255.255.0.0)	16,384	65,534
C	192-223	/24 (255.255.255.0)	2,097,152	254

Examples:

Class A: 10.0.0.1 (Large networks like ISPs)
Class B: 172.16.0.1 (Medium networks like universities)
Class C: 192.168.1.1 (Small networks like offices)

Address Format:

Class A: N.H.H.H (N=Network, H=Host)
Class B: N.N.H.H
Class C: N.N.N.H

Mnemonic: "A for All (large), B for Business (medium), C for Company (small)"

Question 4(b OR) [4 marks]

If number of nodes in mesh topology are 11 than find minimum number of required links.

Answer:

Formula for Mesh Topology: Number of links = n(n-1)/2

Where n = number of nodes

Given: Number of nodes = 11

Calculation: Number of links = 11(11-1)/2 = 11 × 10/2 = 110/2 = 55

Answer: Minimum number of required links = 55

Explanation:

In mesh topology, every node connects to every other node
Each node has (n-1) connections
Total connections = n(n-1), but each link counted twice
Therefore, actual links = n(n-1)/2

Mnemonic: "Every node connects to Every other"

Question 4(c OR) [7 marks]

Explain domain name system (DNS) with diagram.

Answer:

DNS translates human-readable domain names into IP addresses for network routing.

DNS Hierarchy:

graph TB
    subgraph "DNS Hierarchy"
        Root["Root Servers (.)"]
        TLD["Top Level Domain (.com, .org, .edu)"]
        SLD["Second Level Domain (google, example)"]
        Sub["Subdomain (www, mail, ftp)"]
    end
    
    Root --> TLD
    TLD --> SLD
    SLD --> Sub
    
    subgraph "DNS Resolution Process"
        Client[Client] --> Local[Local DNS Server]
        Local --> RootNS[Root Name Server]
        RootNS --> TLDNS[TLD Name Server]
        TLDNS --> AuthNS[Authoritative Name Server]
        AuthNS --> Local
        Local --> Client
    end

DNS Components:

Component	Function	Examples
Root Servers	Top-level authority	13 root servers worldwide
TLD Servers	Manage top-level domains	.com, .org, .edu, .gov
Authoritative Servers	Hold actual DNS records	Company DNS servers
Local DNS Servers	Cache and forward queries	ISP DNS servers

DNS Record Types:

A Record: Maps domain to IPv4 address
AAAA Record: Maps domain to IPv6 address
CNAME: Creates domain aliases
MX Record: Specifies mail servers
NS Record: Identifies name servers

Resolution Process:

Client Query: User enters domain name
Local Cache Check: Check local DNS cache
Recursive Query: Local server queries hierarchy
Response Return: IP address returned to client

Caching: Improves performance and reduces network traffic
Redundancy: Multiple servers ensure availability
Load Distribution: Balances query load across servers

Mnemonic: "Domains Need Systematic name-to-address translation"

Question 5(a) [3 marks]

Explain the need of IPv6.

Answer:

IPv6 was developed to address limitations of IPv4 and support future internet growth.

Key Requirements:

Problem	IPv4 Limitation	IPv6 Solution
Address Space	4.3 billion addresses	340 undecillion addresses
NAT Complexity	Private-public translation	End-to-end connectivity
Security	Optional IPSec	Built-in IPSec support
Mobile Support	Limited mobility	Native mobility support

Critical Needs:

IoT Explosion: Billions of connected devices need unique addresses
Mobile Growth: Smartphones and tablets require internet access
Global Connectivity: Emerging markets joining internet
Address Format: 128-bit vs 32-bit in IPv4
Simplified Header: More efficient packet processing
No Fragmentation: Routers don't fragment packets

Mnemonic: "IPv6 provides Infinite addresses for Internet growth"

Question 5(b) [4 marks]

Explain confidentiality using Asymmetric Key encryption.

Answer:

Asymmetric encryption uses key pairs (public-private) to ensure data confidentiality.

Encryption Process:

sequenceDiagram
    participant S as Sender
    participant R as Receiver
    
    Note over R: Generate Key Pair
    R->>S: Public Key
    Note over S: Encrypt with Public Key
    S->>R: Encrypted Message
    Note over R: Decrypt with Private Key
    R->>R: Original Message

Key Characteristics:

Aspect	Description	Security Benefit
Public Key	Freely distributed	Anyone can encrypt
Private Key	Kept secret	Only owner can decrypt
Key Pair	Mathematically related	Secure communication
Algorithm	RSA, ECC, DSA	Strong encryption

Confidentiality Process:

Step 1: Receiver generates public-private key pair
Step 2: Public key shared with sender
Step 3: Sender encrypts message with public key
Step 4: Only receiver's private key can decrypt
No Key Exchange: Eliminates key distribution problem
Non-repudiation: Sender cannot deny sending message
Digital Signatures: Authentication and integrity

Mnemonic: "Public locks, Private unlocks"

Question 5(c) [7 marks]

Explain man-in-middle attack with example.

Answer:

Man-in-the-middle attack intercepts communication between two parties without their knowledge.

Attack Process:

sequenceDiagram
    participant A as Alice
    participant M as Mallory (Attacker)
    participant B as Bob
    
    A->>M: Message for Bob
    Note over M: Intercepts & Reads
    M->>B: Modified/Original Message
    B->>M: Reply for Alice
    Note over M: Intercepts & Reads
    M->>A: Modified/Original Reply

Attack Stages:

Stage	Attacker Action	Victim Impact
Interception	Position between parties	Unknown to victims
Decryption	Break/bypass encryption	Access to data
Modification	Alter messages	False information
Re-encryption	Hide tampering	Maintain illusion

Real-world Example:

Scenario: Online banking session
Attack: Attacker on public WiFi intercepts traffic
Method: Creates fake access point "Free_WiFi"
Result: Steals banking credentials and transfers money

Common Targets:

Public WiFi: Coffee shops, airports, hotels
Email Communication: Corporate communications
Online Shopping: Credit card information theft
Social Media: Personal information harvesting

Prevention Measures:

SSL/TLS: End-to-end encryption protocols
VPN Usage: Secure tunnel for all traffic
Certificate Verification: Check website authenticity
Avoid Public WiFi: Use cellular data for sensitive tasks

Mnemonic: "Mallory Intercepts Messages between Alice and Bob"

Question 5(a OR) [3 marks]

Give the name of OSI model layers with respect to the following devices. 1. Repeater 2. Router 3. Switch

Answer:

Device-Layer Mapping:

Device	OSI Layer	Layer Name	Function
Repeater	Layer 1	Physical Layer	Signal amplification
Router	Layer 3	Network Layer	IP routing decisions
Switch	Layer 2	Data Link Layer	Frame switching

Detailed Functions:

Repeater: Regenerates electrical signals to extend network distance
Router: Makes forwarding decisions based on IP addresses
Switch: Forwards frames based on MAC addresses

Mnemonic: "Repeaters work Physically, Switches link Data, Routers route Networks"

Question 5(b OR) [4 marks]

Explain confidentiality using Symmetric Key encryption.

Answer:

Symmetric encryption uses single shared key for both encryption and decryption.

Encryption Process:

graph LR
    subgraph "Symmetric Encryption"
    direction LR
        PT[Plain Text] --> E[Encryption]
        K[Shared Key] --> E
        E --> CT[Cipher Text]
        CT --> D[Decryption]
        K --> D
        D --> PT2[Plain Text]
    end

Key Characteristics:

Feature	Description	Example
Single Key	Same key for encrypt/decrypt	AES-256 key
Fast Processing	Efficient algorithms	Real-time communication
Key Distribution	Secure key sharing required	Pre-shared keys
Algorithm Types	Block and stream ciphers	AES, DES, RC4

Confidentiality Mechanism:

Shared Secret: Both parties must have same key
Encryption: Sender encrypts with shared key
Transmission: Cipher text sent over insecure channel
Decryption: Receiver decrypts with same key
Advantages: Fast execution, low computational overhead
Disadvantages: Key distribution challenge, scalability issues
Applications: VPN tunnels, file encryption, database security

Mnemonic: "Same key Encrypts and Decrypts"

Question 5(c OR) [7 marks]

Explain denial of service attack with example.

Answer:

DoS attack makes network resources unavailable to legitimate users by overwhelming the system.

Attack Types:

graph TB
    subgraph "DoS Attack Types"
        V[Volume-based]
        P[Protocol-based]
        A[Application-based]
    end
    
    V --> VE[Volumetric Examples]
    P --> PE[Protocol Examples]
    A --> AE[Application Examples]
    
    VE --> UDP[UDP Flood]
    VE --> ICMP[ICMP Flood]
    
    PE --> SYN[SYN Flood]
    PE --> SMURF[Smurf Attack]
    
    AE --> HTTP[HTTP Flood]
    AE --> SLOW[Slowloris]

Attack Categories:

Type	Method	Target	Impact
Volume-based	Flood with traffic	Bandwidth	Network congestion
Protocol-based	Exploit protocol weakness	Server resources	Service unavailability
Application-based	Target application layer	Application server	Service degradation

Real-world Example - DDoS on E-commerce:

Target: Online shopping website during sale season
Method: Botnet of 10,000 infected computers
Attack: Each bot sends 100 requests per second
Result: 1 million requests/second overwhelm servers
Impact: Website crashes, customers cannot purchase, revenue loss

Common DoS Techniques:

SYN Flood: Exploits TCP handshake process
UDP Flood: Sends large number of UDP packets
Ping of Death: Oversized ping packets crash systems
Slowloris: Keeps connections open to exhaust server

Defense Strategies:

Rate Limiting: Restrict requests per IP address
Firewall Rules: Block suspicious traffic patterns
DDoS Protection Services: CloudFlare, AWS Shield
Load Balancing: Distribute traffic across servers
Traffic Analysis: Monitor for abnormal patterns

Business Impact:

Revenue Loss: Customers cannot access services
Reputation Damage: Users lose trust in reliability
Operational Cost: Resources spent on mitigation
Legal Issues: SLA violations, compliance problems

Mnemonic: "Deny service by Overwhelming with requests"