IT 72-Mobile Communication 2-MARK Questions and Answers

UNIT-I

1. Why are electromagnetic waves with very low frequency not used for data transmission in

computer networks?

Low frequency has longer wavelength

Data rates depends upon the bandwidth

2. Differentiate hard and soft handoff?

Hard hand off

Existing connection must be broken before a new connection is established

There is a short break in transmission which can be noticed by the user

Soft hand off

A new connection is established before the old one is released

3.How are guard spaces realized between users in CDMA?

The guard space between a pair of users in CDMA systems is the orthogonality between

their spreading codes. The lower the correlation between any pair of spreading codes is, the

better is the user separation.

4. What are the benefits of reservation schemes?

No other station is allowed to transmit during that slot

Avoidance of congestion

Waiting time is clearly known

5. Define a cell.

In mobile communication, the coverage area is divided into smaller areas which are each

served by it’s own base station. These smaller areas are called cells.

6. What is frequency reuse?

Spatially reusing the available spectrum so that the same spectrum can support multiple

users separated by a distance is called frequency reuse.

7. Mention the various multiple access schemes used in wireless communication.

Frequency Division Multiplexing Access, Time Division Multiplexing Access and Code

Division Multiplexing Access

8. What is co-channel interference?

Interference between signals from co channels are termed as co channel interference

9. What is adjacent channel interference?

Interference resulting from signals which are adjacent in frequency to the desired signal

is called adjacent channel interference.

10. Mention the different types of cells.

Femto cells, pico cells, micro cells, macro cells and mega cells.

11. What is a picocell?

Small cells inside a building that support local indoor networks such as wireless LANs.

Size of these cells are in the range of few tens of meters.

12. What is cellular topology?

Cellular topology refers to infrastructure topology employing frequency reuse concept.

13.What are the various channel allocation techniques used in cellular communication?

Fixed Channel Allocation, dynamic channel allocation and hybrid channel allocation.

14.What is a cluster?

The N cells which collectively use the complete set of available frequencies is

called a cluster.

15.What are the technical issues in planning of a cellular network?

Selection of frequency reuse pattern for different radio transmission techniques

Physical deployment and radio coverage modelling

Plans to account for the growth of the network

Analysis of the relationship between the capacity, cell size and the cost of infrastructure

16.What is cell splitting?

This is the process of subdividing a congested cell into smaller cells, each with it’s own

base station and a corresponding reduction in antenna height and transmitter power. Cell splitting

increases the capacity of a cellular system since it increases the number of times that channels

are reused.

17.What is cell sectoring?

The co channel interference in a cellular system may be decreased by replacing a single

omni directional antenna at the base station by several directional antennas, each radiating within

a specified sector. By using directional antennas, a given cell will receive interference and

transmit with only a fraction of the available co channel cells. This technique for reducing co

channel interference and thus increasing system performance by using directional antennas is

called sectoring.

18. What is a page?

It is a brief message which is broadcast over the entire service area, usually in a simulcast

fashion by many base stations at the same time.

19. What are the channels used in mobile communication systems?

Forward voice channels (FVC)

Reverse voice channels (RVC)

Forward control channels (FCC)

Reverse Control channels (RCC)

20. What are the basic units of a Cellular system?

Mobile stations

Base stations

Mobile Switching Center (MSC) or Mobile Telephone Switching Office (MTSO).

21. What are the limitations of conventional mobile telephone system?

Limited service capability

Poor service performance

Inefficient frequency spectrum utilization

22. What are the disadvantages of cellular systems with small cells?

Requires complex infrastructure

Requires frequent hand-over

Involves complicated frequency planning

UNIT-II

1.Is IEEE 802.11 and Wi-Fi same?State the purpose of WiFi

Ans: No ,WiFi is wireless internet. The laptop has an internal wireless card so it can be

connected to wireless routers.No need to have an Ethernet cable to connect to the web.

2.What are the various types of wireless network topologies?

Infrastructure network topology and ad hoc topology.

3.What are the classifications of Wireless technologies and systems?

Cellular mobile radio systems

Cordless telephones

Wide-area wireless data systems

High-speed WLANs

Paging/messaging systems

Satellite-based mobile systems

4. Define BCA.

Borrowing Channel Allocation is a method by which more frequencies are allotted

dynamically for high traffic cells.

5.Why 800 MHz frequency is selected for mobiles?

Fixed Station Services - 30 MHz to 100 MHz

Television Broadcasting - 41 MHz to 960 MHz

FM Broadcasting - 100 MHz

Air to Ground system - 118 MHz to 136 MHz

Maritime mobile services - 160 MHz

Military Aircraft use - 225 MHz to 400 MHz

Frequency bands between 30 MHz to 400 MHz is crowded with large number of services

and above 10 GHz is not used due to propagation path loss, multipath fading and

improper medium due to rain activity. So 800 MHz is chosen for mobile communication.

6. Mention the function of the base station.

The base station serves as a bridge between all mobile users in the cell and connects the

simultaneous mobile calls via telephone lines or microwave links to the mobile switching

center(MSC)

7. What are the functions of MSC?

The MSC coordinates the activities of all the base stations and connects the entire cellular

system to the PSTN.

8. Define foot print.

The actual radio coverage of a cell is known as the foot print. It is determined from field

measurements or propagation prediction models.

9. Mention the basic propagation mechanisms, which impact propagation in mobile

communication.

The basic propagation mechanisms are,

Reflection

Diffraction

Scattering

10.What is reflection?

Reflection occurs when a propagating electromagnetic wave impinges upon an object,

which has very large dimension when compared to the wavelength of propagating wave.

11. What is diffraction?

Diffraction occurs when the radio path between the transmitter and receiver is obstructed

by a surface that has sharp irregularities.

12. What is scattering?

Scattering occurs when the medium through which the wave travels consists of objects

with dimensions that are small compared to the wavelength and where the number of obstacles

per unit volume is large.

13. What are the principles of Cellular Architecture?

o Low power Transmitters and Coverage Zones.

o Frequency Reuse.

o Cell splitting to increase Capacity.

o Hand off and Central Control.

14. State the expression used to locate co channel cells.

N = i2 + ij + j2

15. Define co channel cells.

The cells that operate with the same set of frequencies are referred as co channel cells.

16.Write some features of TDMA?

In TDMA , no. of time slots depends upon modulation technique ,available bandwidth

Data transmission occurs in bursts It uses different time slots for transmission and

reception, then duplexers are not required

Adaptive equalization is necessary

Guard time should be minimized

17.Write some features of CDMA?

In CDMA system, many users share the same frequency either TDD or FDD may be used

Channel data rate is high

Multipath fading may be substantially reduced

CDMA uses co –channel cells, it can use macroscopic spatial diversity to provide soft

hand off

18.What is near-far effect in wireless network?

When used with FM or spread spectrum modulation, it is possible for the strongest user

to successfully capture the intended receiver , even when many users are also transmitting . If the

closest transmitter is able to capture a receiver because of small propagation path loss, it is called

as near –far effect in wireless network

19.What is the primary goal of IEE 802.11?

The primary goal of the standard was the specification of a simple, robust, WLAN which

offers time bounded and asynchronous services also it should be able to operate with multiple

physical layers

20.What are Advantages of wireless LAN?

Flexibility

Planning

Design

Robustness

Quality Service

Cost

Proprietary Solution

Restriction

Safety and Security

21.What are Design Goals of Wireless LAN?

Global Operation

Low Power

License-free Operation

Robust transmission technology

Simplified spontaneous co-operation

Easy to use

protection of investment

Safety and Security

Transparency for application.

UNIT-III

1.What is mobility management?

Mobility management refers to the operations required for tracking the mobile and

restructuring existing connections as it moves. Mobility management consists of Location

management and Handoff management

2.Define location management and handoff management.

Location management refers to the activities a wireless network should perform in order

to keep track of where the mobile is.

Handoff management handles the messages required to make the changes in the fixed

network to handle the change in location during a ongoing communication.

3.What is meant by GPRS?

General packet radio services, a technology for radio transmission of small packets of

data, esp. between cellular phones and the Internet

4.What do you meant by roaming?.

Extending of connectivity service in a location that is different from the home location

where the service was registered. Roaming ensures that the wireless device is kept connected to

the network, without losing the connection.

5. What are types of Handover?

Intra-cell handover Inter-cell , intra- BSC handover Inter-BSC, intra-MSC handover Inter

MSC handover

6.What are subsystems in GSM system?

Radio subsystem(RSS)

Network & Switching subsystem(NSS)

Operation subsystem(OSS)

7.What are the information in SIM?

card type, serial no, list of subscribed services

Personal Identity Number(PIN)

Pin Unlocking Key(PUK)

An Authentication Key(KI)

8. What is GSM?

GSM stands for Global System for mobile Communication. This is the most successful

digital mobile telecommunication system.this is second generation and it permits integration of

voice and data services.

9.What are the basic elements of telecommunication systems?

Transmitter – it takes the information and converts into signal

Transmission medium – it carries the signal

Receiver – receives the signal and converts it back into usable information.

10. List the databases of NSS in GSM?

Home location register

Visitor location register

Authentication center

11. What are the functions of OSS in GSM?

Manage all charging and billing procedures

Manage all mobile equipment in the system

12. What are the services offered by the GSM?

There are three user services offered by GSM, they are

Bearer or data service

Telephone service

Supplementary ISDNservice

13. What are the logical channels in GSM?

Traffic channels(TCH)

Control Channels(CCH)

14. What are the security services of GSM?

Access control and authentication

Confidentiality

Anonymity

15. What is MSC ?

Main Service Channel (MSC) carries all user data.eg. audio, multimedia data.

16.What is FIC ?

The Fast Information Channel(FIC) contains Fast Information Block(FIB) with 256bits

each(16 bit checksum). An FIC carries all control information which is required for interpreting

the configuration and content of the MSC.

17.What is meant by beacon?

A beacon contains a timestamp and other management information used for power

management and roaming. e.g., identification of the base station subsystem(BSS)

18.What is Active scanning?

Active scanning comprises sending a probe on each channel and waiting for response.

Beacon and Probe response contain the information necessary to join the new BSS.

19. What is Passive Scanning?

Passive Scanning Simply means listening into the medium to find other networks, i.e.

receiving the beacon of another network issued by the synchronization function within an access

point

20.What do you mean by Polling?

Polling is a strictly centralized scheme with one master and several slave stations. The

master can collect the list of stations during the contention phase and can poll these slaves

according to many schemes like round robin, random access, reservation scheme etc.

UNIT-IV

1. What is MobileIP?

Mobility in the network layer is termed as Mobile IP.

2. What are the requirements of Mobile IP?

Compatibility

Transparency

Scalability and Efficiency

Security

3. Define COA.

A COA defines the current location of the MN from an IP point of view. All IP packets

sent to the MN are delivered to the COA, not directly to the IP address of the MN. Packet

delivery toward the MN is done using a tunnel.

4. What is Co-located COA?

A COA is called co-located if the Mobile Node temporarily acquired an additional IP

address which acts as a COA. This address is now topologically correct, and the tunnel endpoint

is at the mobile node.

5. What is encapsulation and decapsulation?

Encapsulation is the mechanism of taking a packet consisting of packet header and data

and putting it into the data part of a new packet. The reverse operation, taking a packet out of the

data part of another packet, is called decapsulation.

6. What is the purpose of GRE?

GRE allows the encapsulation of packets of one protocol suite into the payload portion of

a packet of another protocol suite. The packet of one protocol suite with the original packet

header and data is taken and a new GRE header is prepended. Together this forms the new data

part of the new packet.

7. What do you mean by binding request?

Any node that wants to know the current location of the mobile node can send a binding

request to the home agent/ the home agent can check if the MN has allowed dissemination of its

current location. If the HA is allowed to reveal the location it sends back a binding update.

8. What are the enhancements made in DSDV?

DSDV adds to things to the Distance vector algorithm,

Sequence Number

Damping

9. What is Route Maintenance?

If a node is continuously sending packets via a route . it has to make sure that the route is

held upright. As soon as a node detects problems with the current route, it has to find an alternate

route.

10. What is route discovery?

A node only tries to discover a route to a destination of it has to send something to this

destination and there is currently no known route. If a node needs to discover a route, it

broadcasts a route request with a unique identifier and the destination address as parameters.

11. What is DHCP?

DHCP stands for Dynamic Host Configuration Protocol, meant for automatic

configuration of IP address.

12. What is the purpose of DHCPREQUEST?

When the client sends a DHCP discover message the server responds with the DHCP

offer message and offers a list of configuration parameters. Now the client can choose among

one of the offered configurations and rejecting the others using DHCPREQUEST.

13. What should be done to optimize the route discovery?

Too many broadcasts can be avoided by maintaining a counter. A node can cache path

fragments from recent requests.A node can also update this cache from packet headers.

14. What are the metrics should be considered while routing?

Number of hops

Interference

Reliability and Error rate

15. What is binding warning?

If a node decapsulates a packet for an MN, but it is not the current FA for this MN, this

node sends a binding warning to the HA of the MN. The warning contains the IP address of the

MN and the address of the node that has tried to send the packet to this MN. The HA should now

send binding update to the node that obviously has a wrong COA for the MN.

16. What is the main purpose of registration request in mobile IP?

The main purpose of registration is to inform the HA of the current location for correct

forwarding of packets. Registration is done by mobility binding

17. What do you mean by mobility binding?

The MN sends its registration request containing the COA to the FA which is forwarding

the request to the HA. The HA now sets up a mobility binding containing the mobile nodes home

IP address and the current COA.

18. What are the services provided by the foreign agent?

The FA can provide serveral services to the MN during its visist in the foreign network.

The FA can have the COA thus acting as tunnel endpoint and forwarding packets to the MN.

Furthermore the FA can be a default router for the MN. The FA can also provide security

services.

19. What is Foreign agent COA?

The COA could be located at the FA, ie., the COA is an IP address of the FA. Thus the

FA is the tunnel end point and forwards packets to the MN. many MN using the FA can share

this COA as common COA.

20. Mention the steps to deliver the packet in MobileIP.

Identification of current location of MN

Encapsulation and tunnelling of packets by HA

Decapsulation of packets by FA

MN receiving the packet.

21. Define tunnelling.

Tunnel establishes a virtual pipe for data packets between tunnel entry and tunnel

endpoint.Packets entering the tunnel are forwarded inside the tunnel and leave the tunnel

unchanged.

22. Why is routing in multihop adhoc networks complicated?

Traditional routing algorithms will not work efficiently

Centralised approaches will not work

Forwarding a packet in the case of unknown topology is flooding.

23. What are the two parts of DSR?

Route Discovery

Route Maintenance

24. What is proactive routing?

It maintains fresh lists of destinations and their routes by periodically distributing routing

tables throughout the network.

25. What is Reactive routing?

It finds a route on demand by flooding the network with route request packets.

26. What is multicasting?

The delivery of packets from one or more senders to a group of receivers.

UNIT-V

1.What is WAP?

Wireless application protocol(WAP) is a common effort of many companies and

organizations to set up a framework for wireless and mobile web access using many different

transport systems. Eg. GSM, GPRS, UMTS.

2. List the interfaces used in WAP architecture

Transport layer service access point

Security service access point

Transaction service access point

Appication service access point

3. What is the use of WAE?

The application layer with the Wireless Application Environment (WAE) offers a

framework for the integration of different www and mobile telephony application.

4.What are the benefits of using WTP?

It offers several advantages to higher layers, including an improved reliability over

datagram services, improved efficiency over connection oriented service, and support for

transaction oriented services such as web browsing.

5.How does the WTP achieves reliability?

The reliability can be achieved by duplicate removal, retransmission, acknowledgements

and unique transaction identifiers.

6.What are the features of WSP?

Session management

Capability management

Content management

7.List the basic features of WML?

The WML includes serveral basic features such as

Text and images

User interaction

Navigation

Context management

8.What is WDP?

The wireless datagram protocol operates on top of many different bearer services capable

of carrying data. The WDP offers more or less the same services as the UDP.In order to

multiplexing and demultiplexing of data the WDP offers a source anddestination port numbers.

9.What is WTA?

The wireless telephony application is a collection of telephony specific extension for call

and feature control mechanisms, merging data networks and voice networks.

10.What is WAP 2.0?

The WAP 2.0 continues to support WAP 1.x protocols but it additionally integrates IP,

TCP, TLS and HTTP. It supports WML as well as XHTML with a mobile profile.

11.What are the benefits of using WAP?

Interoperable

Scalable

Efficient

12. What is the use of WCMP?

The wireless control message protocol is used to provide the error handling mechanism

for WDP. It contains control messages that resemble the ICMP messages for IPV4. it can be used

for WDP nodes and gateways.

13.What is WTLS?

The Wireless transport layer security can provide different levels of security i.e., privacy,

data integrity, and authentication and it has been optimized for low bandwidth, high delay bearer

networks. It supports datagram and connection oriented transport layer protocols.

14.Define snooping TCP.

The FA buffers all packets with destination mobile host and additionally snoops the

packet flow in both directions to recognize acknowledgements is called snoopingTCP.

15.What is WML?

Wireless Markup Language is a tag based browsing language for screen management,

data input, hyperlinks and navigation support.

16. What is WML script?

Complement to WML. Derived from javascript. Provides general scripting capabilities.

17.What is WMLBrowser?

WMLBrowser is a library that provides several functions typical for a browser,such as

prev to go back one card or refresh to update the context of the user interface.

18.Define WAP

WAP is Wireless Application Protocol.It is the basic Objetive of the WAP forum are to

bring diverse Internet content and others data service to digital cellular phones and other

wireless,mobile terminals.Moreever a protocol suite should enable global wirless communication

across different wireless network technologies.All WAP forum solution must

be:interoperable,scaleable,efficient,reliable.

19.What is HTTP?

The Hypertext transfer protocol is a stateless, lightweight, application level protocol for

data transfer between servers and clients. An HTTP transaction consists of an HTTP request

issued by a client and an HTTP response from the server. Stateless means that all HTTP

transactions independent of each other.

20.What is image scaling?

If a page contains a true color, high-resolution picture, this picture can be scaled down to

fewer colors, lower resolution, or finally to only the title of the picture. The user can decide to

download the picture separately. Further one can offer clipping, zooming, or detail studies to

users if they are interested in a part of the picture.