(SEM VII) THEORY EXAMINATION 2022-23 MOBILE COMPUTING

SECTION A – Short Answers (2 Marks Each)

(a) Mobile Computing

Mobile computing refers to the ability to use computing devices such as smartphones, tablets, or laptops while moving, using wireless communication networks to access data, applications, and services anytime and anywhere.

(b) Soft handoff vs Hard handoff

In hard handoff, the connection with the old base station is broken before establishing a new one (break-before-make).
In soft handoff, the mobile device maintains connections with multiple base stations simultaneously (make-before-break), ensuring better call continuity.

(c) Collisions on PHY and MAC layer

PHY layer collisions occur due to signal interference at the physical medium, while MAC layer collisions occur due to simultaneous frame transmissions because of contention in channel access.

(d) Mobile IP

Mobile IP is a protocol that allows a mobile node to maintain the same IP address while moving across different networks by using home agents and foreign agents.

(e) Need of mobile database

Mobile databases support data access in mobile environments, handle disconnections, enable local storage, and provide data consistency and synchronization for mobile users.

(f) Data replication and performance

Data replication improves performance by reducing access latency, increasing data availability, and minimizing network traffic by storing copies of data closer to users.

(g) Kangaroo transaction processing

Kangaroo transaction processing allows transactions to migrate between different database servers as a mobile user moves across cells, ensuring transaction continuity.

(h) Mobile agent functioning

A mobile agent is a program that migrates across network nodes, executes tasks locally, collects results, and returns them to the originating system, reducing network load.

(i) Temporary Ordered Routing Algorithm (TORA)

TORA is a distributed routing protocol for MANETs that uses link reversal to maintain routes and supports multiple paths with fast route repair.

(j) Routing algorithms used in MANETs

Common MANET routing algorithms include DSDV, DSR, AODV, TORA, and Fisheye State Routing.

SECTION B – Long Answers (10 Marks Each)

(a) Cellular system with three-level and seven-level clustering

A cellular system divides a geographical area into cells. In three-cell clustering, frequencies are reused every three cells, offering higher capacity but more interference. In seven-cell clustering, interference is reduced but capacity decreases.
Merits include efficient spectrum utilization and scalability, while demerits include handoff complexity and interference management.

(b) Bluetooth and Bluetooth protocol stack

Bluetooth is a short-range wireless communication technology used for personal area networks.
The Bluetooth stack consists of Radio layer, Baseband, Link Manager Protocol (LMP), Logical Link Control and Adaptation Protocol (L2CAP), and Application layer, each handling transmission, connection management, and data services.

(c) Design of Coda file system and states of Venus

Coda is a distributed file system designed for mobile computing. It uses Venus (client) and Vice (server).
Venus operates in states such as hoarding, emulation, and reintegration. Hoarding prepares files for disconnection, emulation supports offline operation, and reintegration synchronizes updates after reconnection.

(d) Mobile agent system and related issues

A mobile agent system allows software agents to move across network nodes.
Security issues include authentication, authorization, data integrity, and protection from malicious hosts. Performance issues include migration cost, execution delay, and resource consumption.

(e) QoS in mobile ad-hoc networks

QoS in MANETs addresses parameters such as bandwidth, delay, jitter, packet loss, and energy efficiency. Providing QoS is challenging due to dynamic topology, limited bandwidth, and node mobility.

SECTION C – Long Answers (10 Marks Each)

3(a) GSM architecture and its elements

GSM architecture consists of Mobile Station (MS), Base Station Subsystem (BSS), Network Switching 

Subsystem (NSS), and Operation Support System (OSS).
These components handle communication, mobility management, call routing, authentication, and billing.

3(b) Multiplexing techniques & CSMA/CD suitability

Multiplexing techniques include FDMA, TDMA, and CDMA.
CSMA/CD is not suitable for wireless LANs because collision detection is difficult due to hidden node problem, signal attenuation, and half-duplex communication.

4(a) IEEE 802.11 protocol stack

The 802.11 stack includes the Physical layer, MAC sub-layer, and frame architecture.
The PHY layer handles modulation and transmission, MAC controls access using CSMA/CA, and frame architecture defines data, control, and management frames.

4(b) Entities of Mobile IP and data transfer

Entities include Mobile Node, Home Agent, Foreign Agent, and Correspondent Node.
Data transfer involves tunneling packets from the home agent to the mobile node when it is away from its home network.

5(a) Adaptive clustering in wireless networks

Adaptive clustering dynamically groups nodes into clusters based on mobility, energy, or distance. A cluster head manages communication, reducing routing overhead and improving scalability.

5(b) Data management issues & replication strategies

Issues include disconnections, limited bandwidth, consistency, and synchronization. Replication strategies include full replication, partial replication, and adaptive replication based on access patterns.

6(a) Mobile transaction management schemes

Schemes include two-phase commit, kangaroo transactions, and split transactions.
Issues include disconnections, data consistency, concurrency control, and recovery.

6(b) Agent advertisement in packet forwarding

Agent advertisement informs mobile nodes about available agents and network parameters.
The message format includes agent address, lifetime, care-of address, and supported services.

7(a) MANET characteristics & DSR routing

MANETs are self-configuring, infrastructure-less, dynamic, and energy-constrained.
DSR uses route discovery to find paths and route maintenance to handle broken links.

7(b) Routing protocols

DSDV uses sequence numbers to maintain loop-free routing tables.
Fisheye State Routing reduces overhead by exchanging detailed routing information for nearby nodes and less detail for distant nodes.