Mobile Computing B.Tech 8th Semester PYQ

B.TECH 8th Sem Mobile Computing PYQ

Short Answer Type 

a) Distinguish between infrastructure-based network and adhoc network.

Infrastructure-based network refers to a type of network that consists of fixed base stations that are used to connect mobile devices. In contrast, an adhoc network is a type of network where mobile devices communicate directly with each other without the need for a fixed base station.

Infrastructure-based Network	Ad hoc Network
Centralized architecture with a fixed infrastructure	Decentralized architecture without a fixed infrastructure
Uses access points to connect wireless devices to the wired network	Wireless devices communicate directly with each other without the need for an access point or central server
Provides a wider range of services and greater coverage area	Limited coverage area and less number of services
Devices have fixed positions	Devices can move frequently
Network configuration and maintenance are centralized	Network configuration and maintenance are distributed
Examples: Wi-Fi networks, cellular networks	Examples: Mobile ad hoc networks (MANETs), wireless sensor networks (WSNs)

b) What is the role of a MAC protocol? Discuss.

MAC protocol (Media Access Control protocol) is responsible for coordinating access to a shared communication medium, such as a wireless channel, in a way that avoids collisions between transmitted data packets. The MAC protocol sets the rules for how different devices in a network will access and use the shared communication medium.

1. MAC (Media Access Control) protocol is a sub-layer of the data link layer in the OSI model.
2. Its main role is to provide access to the physical transmission medium for multiple stations in a network.
3. MAC protocol is responsible for coordinating the access to the transmission medium and ensures that only one station can transmit at a time.
4. It also handles issues such as collision detection and resolution, packet framing, addressing, and error checking.
5. MAC protocols can be classified into two types: contention-based and controlled access.
6. In contention-based MAC protocols, all stations compete for the medium, and the winner transmits the data.
7. In controlled access MAC protocols, the stations follow a predetermined sequence to access the medium, and collisions are avoided.
8. The choice of MAC protocol depends on various factors such as network topology, traffic load, latency requirements, and reliability needs.
9. Examples of popular MAC protocols include CSMA/CD, CSMA/CA, Token Ring, and Polling.

c) Differentiate between FDMA, TDMA and CDMA.

FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) are three different techniques for dividing a communication channel into multiple sub-channels to allow multiple users to share the same channel.

FDMA divides the channel into frequency bands, with each user assigned a unique frequency band. TDMA divides the channel into time slots, with each user assigned a unique time slot. CDMA assigns a unique code to each user and uses that code to separate the user's signal from others on the same frequency band.

In FDMA, users can only access their assigned frequency band, while in TDMA, users can only access their assigned time slot. In CDMA, users can use the entire frequency band, but each user's signal is separated by a unique code.

d) Compare 1G, 2G, 3G and 4G cellular wireless communication technologies. 

1G, or first generation, cellular wireless technology refers to the earliest wireless communication systems that were introduced in the 1980s. These systems were analog and provided only basic voice communication services.

2G, or second generation, cellular wireless technology was introduced in the 1990s. These systems were digital and provided additional services such as SMS, MMS, and internet browsing. The two main 2G technologies are GSM (Global System for Mobile Communications) and CDMA (Code Division Multiple Access).

3G, or third generation, cellular wireless technology was introduced in the early 2000s. These systems provided high-speed data transfer capabilities, enabling services such as mobile internet, video calls, and mobile TV. The two main 3G technologies are UMTS (Universal Mobile Telecommunications System) and CDMA2000.

4G, or fourth generation, cellular wireless technology was introduced in the late 2000s and provided even faster data transfer capabilities than 3G. 4G networks enable services such as high-definition mobile TV, video conferencing, and mobile gaming. The two main 4G technologies are LTE (Long-Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access).

e) Describe Dynamic host configuration protocol.

Dynamic Host Configuration Protocol (DHCP) is a network protocol used to automatically assign IP addresses and other network configuration parameters, such as the subnet mask, default gateway, and DNS servers, to devices on a network. DHCP simplifies network administration by eliminating the need for manual IP address assignments.

When a device connects to a network, it sends a DHCP discover message to request an IP address. The DHCP server on the network then responds with a DHCP offer message that includes the IP address, subnet mask, default gateway, and DNS servers. The device can then accept the offer and receive the assigned IP address and other configuration parameters.

f) Discuss the advantages and disadvantages of Mobile TCP.

Mobile TCP (Transmission Control Protocol) is a protocol used for reliable data transfer over mobile networks. Some advantages and disadvantages of Mobile TCP are:

Advantages:

• Provides reliable data transfer over mobile networks, which are prone to high packet loss and network congestion.
• Maintains a high level of throughput by using techniques such as slow start, congestion avoidance, and fast retransmit.
• Supports selective acknowledgement and retransmission of lost packets, which helps to reduce network congestion.
• Adapts to the changing network conditions by adjusting the congestion window size and retransmission timeout values.

Disadvantages:

• Can lead to long delays due to the time required for retransmission of lost packets.
• Can be affected by mobile network factors such as signal strength, interference, and mobility, which can cause additional packet loss and delays.
• Can consume a significant amount of network resources due to the high number of retransmissions required in congested networks.
• Can be incompatible with some mobile network technologies, such as satellite networks, due to their high latency and low bandwidth.

g) How does slow start help improve the performance of TCP.

Slow start is a technique used in TCP (Transmission Control Protocol) to improve the performance of data transfer over a network. When a connection is established between two devices, slow start is used to gradually increase the amount of data being sent. The sender starts by sending a small amount of data and then increases the amount gradually as acknowledgements are received from the receiver. This prevents network congestion and ensures that data is transmitted efficiently.

h) What are the constraints of mobile device OS?

Mobile device operating systems have several constraints that limit their capabilities compared to desktop operating systems. These constraints include limited processing power, limited memory, limited battery life, and limited screen size. Mobile devices also have limited connectivity options, such as cellular networks and Wi-Fi, which may not always be available or reliable. Additionally, mobile device OSes often have more stringent security requirements due to the sensitive nature of the data being stored and transmitted on these devices.

i) Explain Data dissemination issues in mobile networks.

Data dissemination refers to the process of delivering information or data to multiple users or devices in a network.

In mobile networks, data dissemination can be challenging due to the following issues:

• Limited bandwidth: Mobile networks have limited bandwidth, which can make it difficult to disseminate large amounts of data to multiple devices simultaneously.
• Variable connectivity: Mobile devices can move around and change their connectivity status, which can make it difficult to maintain a consistent data dissemination process.
• Energy constraints: Mobile devices have limited battery life and may need to conserve energy, which can limit the amount of data they can receive or transmit.
• Security concerns: Data dissemination over mobile networks may be susceptible to security threats, such as eavesdropping, interception, or tampering.

To address these issues, mobile networks can use various techniques for data dissemination, such as:

• Caching: Storing frequently accessed data on mobile devices or in a cache server can reduce the amount of data that needs to be disseminated over the network.
• Multicast: Delivering data to multiple devices simultaneously can reduce the bandwidth needed for data dissemination.
• Adaptive streaming: Modifying the quality or quantity of data delivered based on the available bandwidth or device capabilities can optimize data dissemination.
• Content-centric networking: Focusing on content rather than hosts or devices can enable more efficient and flexible data dissemination in mobile networks.

j) Explain the WAP Architecture in brief.

WAP (Wireless Application Protocol) is a set of protocols for accessing information over a mobile wireless network.

It was designed to provide mobile users with access to the internet and other advanced services.

The WAP architecture consists of several layers, each of which performs a specific function in the delivery of data to the mobile device:

• Wireless Application Environment (WAE): provides the application framework for WAP applications.
• Wireless Session Protocol (WSP): provides reliable two-way transmission of data between the mobile device and the WAP gateway.
• Wireless Transaction Protocol (WTP): provides a reliable transport protocol for higher-level protocols like WSP.
• Wireless Transport Layer Security (WTLS): provides security features like encryption, authentication, and data integrity for the WAP communication.
• Wireless Datagram Protocol (WDP): provides a layer for transmitting data over different wireless networks, like GSM, CDMA, etc.

The WAP gateway acts as a proxy between the mobile device and the internet. It translates the WAP protocol into HTTP or other internet protocols.

WAP supports different types of content, including WML (Wireless Markup Language), which is a markup language designed for small screens and low bandwidth networks.

k) What is "Slow Start" in mobile computing? 

• Slow start is a congestion control algorithm used in TCP (Transmission Control Protocol) to avoid network congestion.
• In mobile computing, slow start is used to manage the transmission of data between a mobile device and a wireless network.
• When a connection is established between a mobile device and a network, the slow start algorithm starts by sending a small amount of data (one or two packets) to test the network's capacity.
• If the network can handle the data, the algorithm increases the amount of data sent in each packet, gradually increasing the speed of the transmission.
• If the network becomes congested, the slow start algorithm reduces the amount of data sent in each packet, slowing down the transmission to prevent further congestion.
• Slow start helps to ensure that the network is not overloaded with data, which can cause delays and reduce the quality of service for all users.

l) Differentiate between tunneling and reverse tunneling?

Tunneling is a technique of encapsulating one protocol inside another protocol for secure data transfer over an insecure network. It involves creating a virtual tunnel between two endpoints where data is encapsulated inside the tunneling protocol and sent across the network. The receiver endpoint decapsulates the data by removing the outer protocol layer and extracts the original data.

Reverse tunneling, on the other hand, is a technique where a mobile node behind a firewall or NAT (Network Address Translation) is able to connect to a remote server outside the network by establishing a tunnel in the opposite direction of a normal tunnel. It allows a server outside the network to initiate a connection with a mobile node by encapsulating the request inside a tunnel and sending it to the mobile node.

m) With the help of neat protocol stack, draw and explain three tier architecture for mobile computing.. What are mobile nodes? Explain.

The three-tier architecture for mobile computing consists of three layers:

Mobile client layer: This layer consists of mobile devices that are used for accessing and interacting with the mobile applications. It includes various devices such as smartphones, tablets, wearables, etc.

Application layer: This layer consists of the application servers that provide services to the mobile clients. The services can be anything from social networking, e-commerce, gaming, etc.

Backend layer: This layer consists of the backend servers that store and manage the data for the applications. It includes servers such as database servers, web servers, and application servers.

Mobile nodes refer to any device that is capable of connecting to a mobile network and communicating with other devices. These devices can be smartphones, tablets, laptops, wearables, etc. In the context of mobile computing, mobile nodes are devices that are used to access and interact with mobile applications over a wireless network.

The protocol stack for the three-tier architecture for mobile computing is as follows:

• Application layer protocols: HTTP, HTTPS, FTP, SMTP, POP3, IMAP, DNS, SNMP, etc.
• Transport layer protocols: TCP, UDP, etc.
• Network layer protocols: IP, ICMP, ARP, RARP, etc.
• Data link layer protocols: Ethernet, Wi-Fi, Bluetooth, ZigBee, etc.
• Physical layer protocols: Modulation, coding, error control, etc.

In this architecture, the mobile clients communicate with the application servers using application layer protocols such as HTTP, HTTPS, FTP, etc. The transport layer protocols such as TCP and UDP are responsible for establishing and maintaining the connection between the mobile clients and application servers. The network layer protocols such as IP are responsible for routing the data packets between the mobile clients and application servers. The data link layer protocols such as Wi-Fi, Bluetooth, etc., are responsible for providing wireless connectivity between the mobile clients and the network. Finally, the physical layer protocols are responsible for the transmission and reception of the data packets over the wireless network.