Q.1 Describe the types of wireless applications.
Now a day mobile application is used in every field in real life. Some of them
are.
- In Vehicles
- In Hospitals
- In Business
- In Entertainment
- In Location dependent services
- In Mobile and wireless devices
--Sensor
--Embedded controllers
--Pager
--Mobile phones
--Personal digital assistant
--Laptop
Q.2 What are the limitation of mobile computing?
Range and Bandwidth: In general direct cable connection is
faster than mobile internet conection. 2G, 3G, 4G networks are fast but these
networks are usually available within range of cell phone towers. The main
problem with wireless networks is that it works within limited range.
Security standards: When working mobile, user will use virtual
private network (VPN). VPN should be carefully used. One can easily attack the
VPN through a huge number of networks interconnected through the line.
Power consumption: if a power supply fails or portable
generator is not available then mobile devices are relying on battery power.
These batteries are more expensive.
Transmission interferences: The geographical area is not same
everywhere. So the terrain can interfere with signal reception. The range from
the nearest signal point may also interfere with signal reception. Signals in
tunnels, some buildings, and rural areas are often poor.
Health problem due to Cell Phone: Mobile phone users may use
phone while driving so it may cause accident. Cell phones may interfere with
sensitive medical devices.
Q.3 Describe cell in detail.
The geographic area or cellular service area is divided into small hexagonal
region called cells. It is the basic unit of a cellular system. These cells
collectively provide coverage over larger geographical areas. That is why a
user can communicate through mobile phones even if the equipment is moving
through cells during transmission. Each cell served by its own antenna. In
cellular network adjacent cells are assigned different frequencies to avoid
interference.
Advantages of cellular systems with small cells are the following:
- Higher Capacity
- Less transmission power
- Local interference only
- Robust
Fig: Hexagonal Cells
Q. 4 Describe Handoff in cellular networks.
When a user talks on the mobile phone to other user it may happen that the
mobile station moves from one cell to another. During this conversation signal
may become weak. To solve this problem, the Mobile Switching Center (MSC)
checks the level of the signal every few seconds. If the strength of the signal
is week then the MSC searches a new cell that can provide better communication.
Handoff is the process by which a mobile telephone call is transferred from one
base station to another base station. There are two types of handoff.
- Hard Handoff
- Soft Handoff
Hard Handoff: In this process a mobile station only communicates with one base
station. When the mobile user moves from one cell to another, communication
must first be broken with the previous base station before communication can be
established with the new one.
Soft Handoff: In this process a mobile station can communicate with two base
stations at the same time. This means that a mobile station may continue
communicate with the new base station before link is break off from the old
one.
Q. 5 What is mobile agent?
A mobile agent is a software that can move across the network and represent
various tasks. It is a distributed computing paradigm. So you can think agent
is an independent software program that runs on behalf of a network user. When
mobile agent program is launched by a user then it can travel from node to node
autonomously, and can continue to function even if the user is disconnected
from the network. Mobile agent works in different type of application and area
such as: Internet, Electronic commerce, Mobile Computing, Networking.
Fig: Working of Mobile Agent
Q. 6 What are the different services provided by GSM.
GSM provides the following types of services.
- Bearer services:
- Tele Service:
i. Encrypted voice transmission
ii. Short message service
iii. Emergency number
iv. Data Communication
-Supplementary services:
i. User identification
ii. call redirection
iii. Closed user groups
Bearer services permit transparent and non-transparent, synchronous or
asynchronous data transmission.
Q.7 Explain GSM architecture in detail.
A GSM system consists of three subsystems, the radio sub system (RSS), the
network and switching subsystem (NSS), and the operation subsystem (OSS).
1. Radio subsystem
The radio subsystem (RSS) contains all radio specific entities such as the
mobile stations (MS) and the base station subsystem (BSS). It also contains BTS
and BSC.
Mobile Station
The MS comprises all user equipment (Cell Phone) and software required for
communication with a GSM network. Cell Phone contains the subscriber identity
module (SIM), which stores all user-specific data that is relevant to GSM
network.
Base station subsystem (BSS): A GSM network contains many BSSs, each controlled
by a base station controller (BSC).The main function of BSS are as follows:
- Establishing connection to MS
- Coding/decoding of voice
Base transceiver station (BTS): A BTS comprises of antennas, signal processing,
and amplifiers necessary for radio transmission.
Base station controller (BSC): The BSC controls all the BTS. The main function
of BSC are as follows:
- Reserves radio frequencies.
- Handles the handover.
- Performs paging of the MS.
2. Network and switching subsystem (NSS).
The NSS comprises MSC, HLR and VLR.
Mobile services switching center (MSC): These are high performance digital
switches. An MSC manages several BSCs and provide connections to other MSCs and
to the BSCs via the A interface. Home location register (HLR): It contains all
the user related data such as the mobile subscriber ISDN number (MSISDN),
subscribed services (e.g., call forwarding, roaming restrictions, GPRS), and
the international mobile subscriber identity (IMSI).
Visitor location register (VLR): It is a dynamic database which stores all
important data needed for the Mobile Station users currently in the (location
area) LA that is associated to the Mobile Switching Center.
3. Operation subsystem.
It provides the necessary functions for network operation and maintenance. The
OSS contains the following interties.
- Operation and maintenance center (OMC):
- Authentication Centre (AuC):
- Equipment identity register (EIR):
Q.8 Describe Localization and calling in GSM
Worldwide localization of users and roaming are the main service provided by the
GSM network system. The system always knows where a user currently is, and the
same phone number is valid worldwide. For providing this service GSM updates
the user location periodically. The HLR always contains information about the
current location. VLR responsible for the MS informs the HLR about location
changes. As soon as an MS moves into the new location area (range of new VLR),
the HLR sends all user information needed to the new VLR.
To locate an MS and to address the MS, following numbers are needed:
- Mobile station international ISDN number (MSISDN).
- International mobile subscriber identity (IMSI).
- Temporary mobile subscriber identity (TMSI).
- Mobile station7 roaming number (MSRN).
Q.9 Describe Mobile IP.
Mobile IP is an open standard that allows users to keep the same IP address and
stay connected while roaming between IP networks. Mobile IP provides the
facility to users to keep the same IP address while traveling to a different
network. This ensures that roaming of users could continue communication
without sessions or connections being terminated.
Components of a Mobile IP Network
Mobile IP has the following three components:
- Mobile Node
- Home Agent
- Foreign Agent
The Mobile Node is a device such as a cell phone or laptop. These devices have
software that enables network roaming capabilities.
The Home Agent is a router on the home network that maintains information about
the device's current location. It uses tunneling mechanism to forward packets
from a device on the Internet called a Correspondent Node.
The Foreign Agent is a router that works as the connection point for the Mobile
Node when it roams to a foreign network, delivering packets from the Home Agent
to the Mobile Node.
Q.10 What is Hidden terminals problem?
Suppose that there are three mobile A, B, and C. The transmission range of A
reaches B, but not C. The transmission range of C reaches B, but not A. Finally
the transmission range of B reaches A and C.
A starts sending signal to B, C does not receive this transmission. C also wants
to send data to B and senses the medium. The medium appears to be free, the
carrier sense fails. C also starts sending data. It will create a collision at
B. But A cannot detect this collision at B and continues with its transmission.
A is hidden for C and vice versa.
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