Mobile Computing and Networks (4351602) - Summer 2025 Solution

Question 1(a) [3 marks]

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Explain working of POP protocol.

Answer:

POP (Post Office Protocol) is an email retrieval protocol that downloads emails from server to client device.

Working Process:

• Download-based: Emails stored locally on client device
• Offline access: Can read emails without internet connection
• Single device: Best suited for single device access

Mnemonic: “POP Downloads Once Permanently”

Question 1(b) [4 marks]

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Compare OSI model with TCP/IP model.

Answer:

Comparison between OSI and TCP/IP networking models:

Key Differences:

• Layer count: OSI has 7 layers vs TCP/IP’s 4 layers
• Real-world usage: TCP/IP widely implemented, OSI mostly theoretical
• Protocol independence: OSI is protocol-independent, TCP/IP is protocol-specific
• Header overhead: OSI has more overhead due to additional layers

Mnemonic: “OSI Seven Theoretical, TCP Four Practical”

Question 1(c) [7 marks]

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Explain protocols working at each layer in TCP/IP models.

Answer:

TCP/IP model consists of 4 layers with specific protocols at each layer:

graph TD
    A[Application Layer] --> B[Transport Layer]
    B --> C[Internet Layer]
    C --> D[Network Access Layer]
    
    A1[HTTP, HTTPS, FTP, SMTP, POP, IMAP, DNS] --> A
    B1[TCP, UDP] --> B
    C1[IP, ICMP, ARP, RARP] --> C
    D1[Ethernet, WiFi, PPP] --> D

Layer-wise Protocol Functions:

Protocol Details:

• HTTP/HTTPS: Web communication and secure web communication
• TCP: Reliable, connection-oriented data transfer
• UDP: Fast, connectionless data transfer
• IP: Packet routing and addressing
• ARP: Maps IP addresses to MAC addresses

Mnemonic: “Applications Transport Internet Networks Always”

Question 1(c OR) [7 marks]

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Briefly explain OSI model with all its layers and functionality of each layer

Answer:

OSI (Open Systems Interconnection) model has 7 layers for network communication:

graph TD
    A[Application Layer] --> B[Presentation Layer]
    B --> C[Session Layer]
    C --> D[Transport Layer]
    D --> E[Network Layer]
    E --> F[Data Link Layer]
    F --> G[Physical Layer]

Layer Functions:

Key Features:

• Modular design: Each layer has specific responsibilities
• Protocol independence: Layers can use different protocols
• Standardization: Universal networking reference model

Mnemonic: “All People Seem To Need Data Processing”

Question 2(a) [3 marks]

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Give the difference between ARP and RARP protocols.

Answer:

ARP and RARP are address resolution protocols with opposite functions:

Working Process:

• ARP: “I know IP address, need MAC address”
• RARP: “I know MAC address, need IP address”
• Cache: Both maintain address tables for efficiency

Mnemonic: “ARP Asks Physical, RARP Requests IP”

Question 2(b) [4 marks]

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Explain working of IMAP protocol.

Answer:

IMAP (Internet Message Access Protocol) manages emails on server for multiple device access.

Working Process:

Key Features:

• Server-based: Emails remain on server
• Multi-device: Access from multiple devices
• Synchronization: Changes reflected everywhere
• Selective download: Download only needed emails

Advantages:

• Storage efficiency: Server manages storage
• Accessibility: Access from anywhere
• Backup: Server provides automatic backup

Mnemonic: “IMAP Internet Messages Always Present”

Question 2(c) [7 marks]

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Explain Three-tier architecture of mobile computing with appropriate diagram.

Answer:

Three-tier architecture separates mobile computing into distinct layers:

graph TD
    A[Presentation Tier<br/>Mobile Devices] --> B[Application Tier<br/>Application Server]
    B --> C[Data Tier<br/>Database Server]
    
    A1[Smartphones<br/>Tablets<br/>Laptops] --> A
    B1[Business Logic<br/>Processing<br/>API Services] --> B
    C1[Database<br/>File Systems<br/>Data Storage] --> C

Tier Details:

Architecture Benefits:

• Scalability: Each tier can scale independently
• Maintainability: Separate concerns for easier updates
• Security: Data protection through tier separation
• Performance: Distributed processing reduces load

Communication Flow:

• User request: Presentation → Application → Data
• Response: Data → Application → Presentation
• Processing: Application tier handles business logic

Mnemonic: “Presentation Applies Data Processing”

Question 2(a OR) [3 marks]

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Explain the limitation of Stop-and-wait data link layer protocol.

Answer:

Stop-and-wait protocol has several performance limitations:

Major Limitations:

Performance Issues:

• Bandwidth waste: Link remains idle during wait time
• Timeout problems: Lost ACK causes unnecessary retransmission
• Sequential processing: Cannot send multiple frames simultaneously

Mnemonic: “Stop Waits, Bandwidth Wastes”

Question 2(b OR) [4 marks]

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Explain Advantages of IPV6 over the older IPV4 addressing scheme.

Answer:

IPv6 provides significant improvements over IPv4:

Key Advantages:

Major Benefits:

• Unlimited addresses: Solves address exhaustion problem
• Better performance: Simplified header processing
• Enhanced security: Mandatory encryption support
• Mobility support: Better mobile device connectivity

Additional Features:

• Quality of Service: Built-in QoS support
• Multicast: Improved multicast capabilities
• No fragmentation: Routers don’t fragment packets

Mnemonic: “IPv6 Improves Performance, Security, Addresses”

Question 2(c OR) [7 marks]

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Enlist types of networks available in mobile computing. Explain one of them in detail.

Answer:

Types of Mobile Networks:

Detailed: 4G LTE Network

graph TD
    A[Mobile Device] --> B[eNodeB<br/>Base Station]
    B --> C[Mobility Management Entity<br/>MME]
    B --> D[Serving Gateway<br/>S-GW]
    D --> E[Packet Data Network Gateway<br/>P-GW]
    E --> F[Internet/External Networks]
    C --> G[Home Subscriber Server<br/>HSS]

4G LTE Features:

• High Speed: Up to 100 Mbps download, 50 Mbps upload
• Low Latency: Less than 10ms for real-time applications
• All-IP Network: Packet-switched architecture
• Advanced Antenna: MIMO technology for better coverage

Architecture Components:

• eNodeB: Enhanced base station with advanced features
• MME: Manages mobility and authentication
• Gateways: Handle data routing and external connectivity

Applications: Video streaming, online gaming, IoT connectivity

Mnemonic: “4G LTE: Long Term Evolution”

Question 3(a) [3 marks]

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Explain types of Routing.

Answer:

Routing determines path for data packets across networks:

Types of Routing:

Routing Categories:

• Distance Vector: Uses hop count (RIP)
• Link State: Uses network topology (OSPF)
• Hybrid: Combines both approaches (EIGRP)

Selection Criteria:

• Shortest path: Minimum hops or distance
• Load balancing: Distribute traffic evenly
• Fault tolerance: Alternative routes for failures

Mnemonic: “Static Dynamic Default Routes”

Question 3(b) [4 marks]

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What is Subnetting and supernetting?

Answer:

Subnetting and supernetting manage IP address allocation efficiently:

Comparison:

Subnetting Process:

• Borrowing bits: Take bits from host portion
• Create subnets: Multiple network segments
• Reduce broadcast: Smaller broadcast domains

Supernetting Process:

• Combine networks: Merge adjacent networks
• Route aggregation: Single routing entry
• Reduce routing table: Fewer routing entries

Benefits:

• Subnetting: Better network management, security
• Supernetting: Simplified routing, reduced overhead

Mnemonic: “Subnetting Splits, Supernetting Sums”

Question 3(c) [7 marks]

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Explain IPV6 Addressing. Why need of IPV6 migration?

Answer:

IPv6 addressing uses 128-bit addresses to solve IPv4 limitations:

IPv6 Address Structure:

Address Format:

Address Types:

• Unicast: One-to-one communication
• Multicast: One-to-many communication
• Anycast: One-to-nearest communication

Need for IPv6 Migration:

Critical Issues:

Migration Benefits:

• Unlimited growth: Supports IoT expansion
• Simplified configuration: Auto-configuration features
• Better performance: Optimized header structure
• Enhanced security: Mandatory encryption

Migration Challenges:

• Dual-stack: Running both IPv4 and IPv6
• Translation: IPv4-IPv6 interoperability
• Training: Staff education requirements

Mnemonic: “IPv6 Infinite Possibilities, Enhanced Security”

Question 3(a OR) [3 marks]

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Determine valid IPv4 address from below. If it is a valid IPv4 address then find its class, Network ID and Host ID. If it’s an invalid IPv4 address, then give a reason.

a. 192.108.102.101 b. 80.54.256.14

Answer:

Analysis:

Address a: 192.108.102.101

• Valid: All octets within range (0-255)
• Class C: First octet 192 (192-223 range)
• Default mask: 255.255.255.0 (/24)

Address b: 80.54.256.14

• Invalid: Third octet is 256
• Rule violation: Each octet must be 0-255
• Correction: Replace 256 with valid value (0-255)

Mnemonic: “Each Octet Maximum 255”

Question 3(b OR) [4 marks]

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Write Short note on Network Address Translation.

Answer:

NAT translates private IP addresses to public IP addresses for internet access:

NAT Process:

NAT Types:

Benefits:

• IP conservation: Multiple devices share one public IP
• Security: Hides internal network structure
• Cost reduction: Fewer public IP addresses needed
• Flexibility: Easy internal network changes

Limitations:

• End-to-end connectivity: Breaks direct communication
• Protocol issues: Some protocols don’t work through NAT
• Performance: Additional processing overhead

Mnemonic: “NAT Networks Address Translation”

Question 3(c OR) [7 marks]

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Explain IPV4 Datagram Header in detail.

Answer:

IPv4 header contains essential information for packet routing:

Header Fields:

Key Functions:

• Routing: Source and destination addresses
• Fragmentation: Handle large packets
• Error detection: Header checksum
• Quality control: Type of service field

Important Values:

• Protocol: TCP=6, UDP=17, ICMP=1
• Flags: Don’t Fragment, More Fragments
• TTL: Prevents infinite loops

Mnemonic: “Version IHL Service Length Identify Fragment TTL Protocol Check Source Destination”

Question 4(a) [3 marks]

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Explain working of Indirect TCP.

Answer:

Indirect TCP splits TCP connection to handle mobile network challenges:

Architecture:

Connection Split:

• Connection 1: Mobile Host ↔ Base Station
• Connection 2: Base Station ↔ Fixed Host
• Proxy function: Base station acts as TCP proxy

Working Process:

• Data flow: Mobile → Base Station → Fixed Host
• ACK handling: Base station manages acknowledgments
• Handover: Connection maintained during movement

Advantages:

• Wireless optimization: Handles wireless link issues
• Mobility support: Seamless handover capability
• Error recovery: Better handling of wireless errors

Mnemonic: “Indirect TCP Through Proxy”

Question 4(b) [4 marks]

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Write Short note on Stop and Wait ARQ Protocol.

Answer:

Stop and Wait ARQ ensures reliable data transmission with error detection and correction:

Protocol Operation:

Error Handling:

Features:

• Sequence numbers: 0 and 1 alternation
• Timeout mechanism: Handles lost frames/ACKs
• Duplicate detection: Prevents duplicate acceptance
• Flow control: Receiver controls transmission rate

Limitations:

• Low efficiency: Only one frame in transit
• Bandwidth waste: Idle time during waiting

Mnemonic: “Stop Send, Wait ACK, Repeat”

Question 4(c) [7 marks]

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Explain Communication Middleware in detail.

Answer:

Communication middleware provides abstraction layer between applications and network services:

graph TD
    A[Mobile Applications] --> B[Communication Middleware]
    B --> C[Network Services]
    
    B1[Message Passing<br/>RPC<br/>Event Handling] --> B
    C1[TCP/IP<br/>Wireless Protocols<br/>Network APIs] --> C

Middleware Types:

Core Services:

Communication Services:

• Message routing: Efficient message delivery
• Protocol conversion: Different protocol handling
• Buffering: Temporary message storage
• Synchronization: Coordinated communication

Reliability Services:

• Error detection: Message integrity checking
• Retransmission: Failed message recovery
• Duplicate elimination: Prevent message duplication
• Ordering: Maintain message sequence

Mobile-Specific Features:

• Location transparency: Hide mobility from applications
• Disconnection handling: Manage network interruptions
• Bandwidth adaptation: Adjust to network conditions
• Power management: Optimize battery usage

Architecture Benefits:

• Abstraction: Hide network complexity
• Portability: Application independence from network
• Scalability: Support growing number of devices
• Interoperability: Different system communication

Examples:

• CORBA: Distributed object communication
• Message Queues: Asynchronous messaging
• Web Services: HTTP-based communication

Mnemonic: “Middleware Manages Mobile Communication”

Question 4(a OR) [3 marks]

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Explain Handover management in mobile IP.

Answer:

Handover management maintains connectivity when mobile device moves between networks:

Handover Process:

Types of Handover:

• Horizontal: Same technology networks
• Vertical: Different technology networks
• Hard: Break-before-make
• Soft: Make-before-break

Management Components:

• Signal monitoring: Continuous signal assessment
• Network discovery: Available network identification
• Decision algorithm: Optimal network selection

Performance Metrics:

• Handover delay: Time to complete switch
• Packet loss: Data lost during handover
• Signaling overhead: Control message cost

Mnemonic: “Handover Helps Maintain Mobility”

Question 4(b OR) [4 marks]

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Explain key functions of Communication Gateways.

Answer:

Communication gateways enable interoperability between different network systems:

Key Functions:

Gateway Services:

Protocol Services:

• Multi-protocol support: Handle various protocols
• Translation efficiency: Fast protocol conversion
• Standards compliance: Follow protocol specifications

Security Services:

• Authentication: Verify user identity
• Authorization: Control access permissions
• Encryption: Protect data transmission
• Firewall: Filter malicious traffic

Performance Services:

• Caching: Store frequently accessed data
• Compression: Reduce data size
• Traffic shaping: Manage bandwidth usage
• Quality of Service: Prioritize critical traffic

Management Features:

• Monitoring: Track gateway performance
• Configuration: Flexible setup options
• Logging: Record activity and errors

Mnemonic: “Gateways Grant Protocol Interoperability”

Question 4(c OR) [7 marks]

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Explain Process of mobile IP.

Answer:

Mobile IP enables device mobility while maintaining IP connectivity:

sequenceDiagram
    participant MN as Mobile Node
    participant HA as Home Agent
    participant FA as Foreign Agent
    participant CN as Correspondent Node
    
    MN->>FA: Agent Solicitation
    FA->>MN: Agent Advertisement
    MN->>HA: Registration Request
    HA->>MN: Registration Reply
    CN->>HA: Data Packet (Home Address)
    HA->>FA: Tunneled Packet
    FA->>MN: Data Packet

Mobile IP Components:

Registration Process:

Phase 1: Agent Discovery

• Advertisement: Agents broadcast availability
• Solicitation: Mobile node requests agent info
• Selection: Choose appropriate foreign agent

Phase 2: Registration

• Request: Mobile node registers with home agent
• Authentication: Verify mobile node identity
• Binding: Create care-of address binding
• Confirmation: Registration acknowledgment

Phase 3: Packet Delivery

• Interception: Home agent intercepts packets
• Tunneling: Encapsulate and forward packets
• Decapsulation: Foreign agent extracts packets
• Local delivery: Forward to mobile node

Tunneling Mechanism:

Key Features:

• Transparency: Applications unaware of mobility
• Triangle routing: Indirect packet delivery
• Location privacy: Hide actual location
• Seamless handover: Maintain connections

Challenges:

• Triangle routing: Inefficient packet path
• Ingress filtering: Firewall compatibility
• Security: Authentication and encryption

Mnemonic: “Mobile IP: Discover Register Tunnel Deliver”

Question 5(a) [3 marks]

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List advantages of WPANs.

Answer:

WPAN (Wireless Personal Area Network) provides short-range connectivity benefits:

Key Advantages:

Technical Benefits:

• Short range: 10-30 feet coverage reduces interference
• Ad-hoc networking: No infrastructure required
• Device mobility: Move freely within range
• Automatic discovery: Devices find each other automatically

Application Advantages:

• Personal devices: Connect phones, tablets, headphones
• IoT integration: Smart home device connectivity
• File sharing: Quick data transfer between devices
• Peripheral connection: Wireless keyboards, mice

Security Benefits:

• Limited range: Reduced eavesdropping risk
• Encryption: Built-in security protocols
• Pairing: Authenticated device connections

Mnemonic: “WPANs: Wireless Personal Area Networks”

Question 5(b) [4 marks]

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Explain steps of packet delivery in mobile IP.

Answer:

Mobile IP packet delivery involves multiple steps to reach mobile devices:

Packet Delivery Steps:

Detailed Process:

Tunneling Mechanism:

• Encapsulation: Add new IP header with care-of address
• Forwarding: Route through internet to foreign network
• Decapsulation: Remove tunnel header at foreign agent
• Local delivery: Standard delivery to mobile node

Mnemonic: “Correspondent Home Foreign Mobile”

Question 5(c) [7 marks]

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Briefly Explain architecture of WLAN with diagram.

Answer:

WLAN (Wireless Local Area Network) architecture provides wireless connectivity within local area:

graph TD
    A[Distribution System<br/>Wired Backbone] --> B[Access Point 1]
    A --> C[Access Point 2]
    A --> D[Access Point 3]
    
    B --> E[BSS 1<br/>Basic Service Set]
    C --> F[BSS 2<br/>Basic Service Set]
    D --> G[BSS 3<br/>Basic Service Set]
    
    E --> H[Wireless Stations]
    F --> I[Wireless Stations]
    G --> J[Wireless Stations]
    
    K[ESS - Extended Service Set] --> A

WLAN Components:

Architecture Types:

Ad-hoc Mode:

• Independent BSS: No access point required
• Peer-to-peer: Direct station communication
• Limited range: Single hop communication
• Temporary networks: Conference, meeting rooms

Infrastructure Mode:

• Access Point: Central coordination
• Distribution System: Connect multiple APs
• Roaming support: Move between BSS areas
• Internet connectivity: Gateway to external networks

Key Features:

• Mobility: Move within coverage area
• Scalability: Add more access points
• Interoperability: IEEE 802.11 standards
• Security: WPA/WPA2 encryption

Services Provided:

• Association: Connect to access point
• Authentication: Verify user credentials
• Data delivery: Reliable frame transmission
• Power management: Battery optimization

Standards:

• 802.11a: 5 GHz, 54 Mbps
• 802.11b: 2.4 GHz, 11 Mbps
• 802.11g: 2.4 GHz, 54 Mbps
• 802.11n: MIMO, 600 Mbps
• 802.11ac: 5 GHz, 1 Gbps+

Mnemonic: “WLAN: Wireless Local Area Network”

Question 5(a OR) [3 marks]

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Explain 5G mobile network features in detail.

Answer:

5G provides revolutionary mobile network capabilities:

Key Features:

Technical Capabilities:

• Enhanced Mobile Broadband: High-speed internet access
• Ultra-Reliable Low Latency: Critical applications
• Massive Machine Communication: IoT device connectivity

Advanced Technologies:

• Millimeter waves: Higher frequency bands
• MIMO: Multiple antenna systems
• Network slicing: Virtual network partitions
• Edge computing: Distributed processing

Applications:

• Autonomous vehicles: Real-time control
• Smart cities: Connected infrastructure
• Industrial IoT: Factory automation

Mnemonic: “5G: Fifth Generation Great Speed”

Question 5(b OR) [4 marks]

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Explain how DHCP works in a mobile network context.

Answer:

DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses in mobile networks:

DHCP Process in Mobile Networks:

Mobile Network Challenges:

Mobile-Specific Features:

• Fast handover: Quick IP assignment during movement
• Lease renewal: Extend IP address validity
• Conflict resolution: Handle duplicate addresses
• Location update: Notify network of device location

Configuration Information:

• IP address: Unique network identifier
• Subnet mask: Network boundary definition
• Default gateway: Router for external communication
• DNS servers: Domain name resolution

Advantages in Mobile Context:

• Automatic configuration: No manual setup required
• Address conservation: Reuse addresses efficiently
• Mobility support: Seamless network transitions

Mnemonic: “DHCP: Discover Offer Request ACK”

Question 5(c OR) [7 marks]

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Explain Bluetooth technology with a neat figure of its protocol stack.

Answer:

Bluetooth provides short-range wireless communication for personal devices:

graph TD
    A[Applications] --> B[Application Layer]
    B --> C[L2CAP<br/>Logical Link Control]
    C --> D[HCI<br/>Host Controller Interface]
    D --> E[Link Manager Protocol<br/>LMP]
    E --> F[Baseband Layer]
    F --> G[Radio Layer]
    
    H[RFCOMM<br/>Serial Port] --> C
    I[SDP<br/>Service Discovery] --> C
    J[OBEX<br/>Object Exchange] --> B

Protocol Stack Layers:

Technical Specifications:

Physical Layer:

• Frequency: 2.4 GHz ISM band
• Hopping: 79 frequency channels
• Modulation: Frequency shift keying
• Power classes: 1mW to 100mW

Network Topology:

Connection Types:

• SCO: Synchronous Connection-Oriented (voice)
• ACL: Asynchronous Connection-Less (data)
• eSCO: Enhanced SCO (improved voice)

Security Features:

• Authentication: Device identity verification
• Authorization: Service access control
• Encryption: Data protection (E0 algorithm)
• Key management: Security key exchange

Bluetooth Versions:

Applications:

• Audio streaming: Headphones, speakers
• File transfer: Documents, photos
• Input devices: Keyboards, mice
• Health monitoring: Fitness trackers

Advantages:

• Low power: Battery-friendly operation
• Easy pairing: Simple device connection
• Interoperability: Universal standard
• Cost-effective: Inexpensive implementation

Mnemonic: “Bluetooth: Radio Baseband LMP HCI L2CAP Applications”