UNIT I

WIRELESS COMMUNICATION FUNDAMENTALS

Introduction – Wireless transmission – Frequencies for radio transmission – Signals – Antennas – Signal Propagation –

Multiplexing – Modulations – Spread spectrum – MAC – SDMA – FDMA – TDMA – CDMA – Cellular Wireless

Networks.

INTRODUCTION

Mobile computing means different things to different people. Ubiquitous, wireless and remote computing Wireless and

mobile computing are not synonymous. Wireless is a transmission or information transport method that enables mobile

computing.

Aspects of mobility:

user mobility: users communicate (wireless) “anytime, anywhere, with anyone”

device portability: devices can be connected anytime, anywhere to the network

Mobility Issues

Bandwidth restrictions and variability

Location-aware network operation

o User may wake up in a new environment

o Dynamic replication of data

Querying wireless data & location-based responses

Busty network activity during connections & handling disconnections

Disconnection

o OS and File System Issues - allow for disconnected operation

o Database System Issues - when disconnected, based on local data

Portability Issues

Battery power restrictions

Risks to data

- Physical damage, loss, theft

- Unauthorized access

- encrypt data stored on mobiles

- Backup critical data to fixed (reliable) hosts

Small user interface

- Small displays due to battery power and aspect ratio constraints

- Cannot open too many windows

- Difficult to click on miniature icons

- Input - Graffiti, (Dictionary-based) Expectation

- Gesture or handwriting recognition with Stylus Pen Voice matching or voice recognition

APPLICATIONS

Vehicles

transmission of news, road condition, weather, music via DAB

personal communication using GSM

position via GPS

local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy

vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance

Emergencies

early transmission of patient data to the hospital, current status, first diagnosis

Replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc.

crisis, war, ...

Travelling salesmen

direct access to customer files stored in a central location

consistent databases for all agents

mobile office

Replacement of fixed networks

remote sensors, e.g., weather, earth activities

flexibility for trade shows

LANs in historic buildings

Entertainment, education,

outdoor Internet access

intelligent travel guide with up-to-date location dependent information

ad-hoc networks for multi user games

Location dependent services

Location aware services

what services, e.g., printer, fax, phone, server etc. exist in the local environment

Follow-on services

automatic call-forwarding, transmission of the actual workspace to the current location

Information services

„push“: e.g., current special offers in the supermarket

„pull“: e.g., where is the Black Forrest Cherry Cake?

Support services

caches, intermediate results, state information etc. „follow“ the mobile device through the fixed network

Privacy

who should gain knowledge about the location

Effects of device portability

Power consumption

limited computing power, low quality displays, small disks due to limited battery capacity

CPU: power consumption ~ CV2f

C: internal capacity, reduced by integration

V: supply voltage, can be reduced to a certain limit

f: clock frequency, can be reduced temporally

Loss of data

higher probability, has to be included in advance into the design (e.g., defects, theft)

Limited user interfaces

compromise between size of fingers and portability

integration of character/voice recognition, abstract symbols

Limited memory

limited value of mass memories with moving parts

Flash-memory or? as alternative

Wireless networks in comparison to fixed networks

Higher loss-rates due to interference

emissions of, e.g., engines, lightning

Restrictive regulations of frequencies

frequencies have to be coordinated, useful frequencies are almost all occupied Low transmission rates

local some Mbit/s, regional currently, e.g., 9.6kbit/s with GSM .Higher delays, higher jitter

connection setup time with GSM in the second range, several hundred milliseconds for other wireless

systems

Lower security, simpler active attacking

radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile

phones

Always shared medium

secure access mechanisms important

Early history of wireless communication

Many people in history used light for communication

heliographs, flags („semaphore“), ...

150 BC smoke signals for communication; (Polybius, Greece)

1794, optical telegraph, Claude Chappe

Here electromagnetic waves are of special importance:

1831 Faraday demonstrates electromagnetic induction

J. Maxwell (1831-79): theory of electromagnetic Fields, wave equations (1864)

H. Hertz (1857-94): demonstrates with an experiment the wave character of electrical transmission

through space(1886, in Karlsruhe, Germany, at the location of today’s University of Karlsruhe)

Wireless systems: overview of the development

cellular phones satellites wireless

LAN

cordless

phones

1992:

GSM

1994:

DCS 1800

2005?:

UMTS/IMT-2000

1987:

CT1+

1982:

Inmarsat-A

1992:

Inmarsat-B

Inmarsat-M

1998:

Iridium

1989:

CT 2

1991:

DECT

199x:

proprietary

1995/96/97:

IEEE 802.11,

HIPERLAN

2005?:

MBS, WATM

1988:

Inmarsat-C

analog

digital

1991:

D-AMPS

1991:

CDMA

1981:

NMT 450

1986:

NMT 900

1980:

CT0

1984:

CT11983:

AMPS

1993:PDC

Areas of research in mobile communication

Wireless Communication

transmission quality (bandwidth, error rate, delay)

modulation, coding, interference

media access, regulations

Mobility

location dependent services

location transparency

quality of service support (delay, jitter, security)

Portability

power consumption

limited computing power, sizes of display, ...

usability

Simple reference model used here

Influence of mobile communication to the LAYER MODEL

Application layer

service location

new applications, multimedia

adaptive applications

Transport layer

congestion and flow control

quality of service

Network layer

addressing, routing, device location

hand-over

Data link layer

authentication

media access

multiplexing

media access control

Physical layer

encryption

modulation

interference

attenuation

frequency

WIRELESS TRANSMISSION - FREQUENCIES FOR RADIO TRANSMISSION

Frequencies for communication

Frequencies for mobile communication

VHF-/UHF-ranges for mobile radio

simple, small antenna for cars

deterministic propagation characteristics, reliable connections

SHF and higher for directed radio links, satellite communication

small antenna, focusing

large bandwidth available

Wireless LANs use frequencies in UHF to SHF spectrum

some systems planned up to EHF

limitations due to absorption by water and oxygen molecules (resonance frequencies)

Weather dependent fading, signal loss caused by heavy rainfall etc.

Frequencies and regulations

ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)

Europe USA Japan

Mobile phones

NMT 453-457MHz, 463-467 MHz; GSM 890-915 MHz,

935-960 MHz; 1710-1785 MHz, 1805-1880 MHz

AMPS, TDMA, CDMA 824-849 MHz, 869-894 MHz; TDMA, CDMA, GSM 1850-1910 MHz, 1930-1990 MHz;

PDC 810-826 MHz, 940-956 MHz; 1429-1465 MHz, 1477-1513 MHz

Cordless telephones

CT1+ 885-887 MHz, 930-932 MHz; CT2 864-868 MHz DECT

1880-1900 MHz

PACS 1850-1910 MHz, 1930-1990 MHz PACS-UB 1910-1930 MHz

PHS 1895-1918 MHz JCT 254-380 MHz

Wireless LANs

IEEE 802.11

2400-2483 MHz HIPERLAN 1 5176-5270 MHz

IEEE 802.11

2400-2483 MHz

IEEE 802.11

2471-2497 MHz

SIGNALS

physical representation of data

function of time and location

signal parameters: parameters representing the value of data

classification

o continuous time/discrete time

o continuous values/discrete values

o analog signal = continuous time and continuous values

o digital signal = discrete time and discrete values

signal parameters of periodic signals:

period T, frequency f=1/T, amplitude A, phase shift

sine wave as special periodic signal for a carrier:

s(t) = At sin(2 ft t + t)

Fourier representation of periodic signals

1

0

1

0

t t

Ideal periodic signal Real composition (based on

harmonics)

Different representations of signals

amplitude (amplitude domain)

frequency spectrum (frequency domain)

phase state diagram (amplitude M and phase in polar coordinates)

Composed signals transferred into frequency domain using Fourier transformation

Digital signals need

infinite frequencies for perfect transmission

Modulation with a carrier frequency for transmission (analog signal!)

ANTENNAS

Isotropic radiator

Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission

Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna

Real antennas always have directive effects (vertically and/or horizontally)

Radiation pattern: measurement of radiation around an antenna

)2cos()2sin(2

1)(

11

nftbnftactgn

n

n

n

Ideal isotropic radiator

Simple dipoles

Real antennas are not isotropic radiators but, e.g., dipoles with lengths /4 on car roofs or /2 as Hertzian dipole,

shape of antenna proportional to wavelength

Example: Radiation pattern of a simple Hertzian dipole

Directed and Sectorized

Often used for microwave connections or base stations for mobile phones (e.g., radio coverage of a valley)

/2

z y

x

z

y x

/4

Antennas: diversity

Grouping of 2 or more antennas

o multi-element antenna arrays

Antenna diversity

o switched diversity, selection diversity

receiver chooses antenna with largest output

diversity combining

combine output power to produce gain

cophasing needed to avoid cancellation

SIGNAL PROPAGATION

Transmission range

communication possible

low error rate

Detection range

detection of the signal possible

no communication possible

Interference range

signal may not be detected

signal adds to the background noise

Signal propagation

Propagation in free space always like light (straight line)

Receiving power proportional to 1/d²

(d = distance between sender and receiver)

Receiving power additionally influenced by

fading (frequency dependent)

shadowing

reflection at large obstacles

scattering at small obstacles

diffraction at edges

+

/4 /4

/2

/2

+

/2

Shadowing Reflection Scattering Diffraction

Multipath propagation

Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction

Time dispersion: signal is dispersed over time

Interference with “neighbor” symbols, Inter Symbol Interference (ISI)

The signal reaches a receiver directly and phase shifted

Distorted signal depending on the phases of the different parts

Effects of mobility

Channel characteristics change over time and location

signal paths change

different delay variations of different signal parts

different phases of signal parts

Quick changes in the power received (short term fading)

Additional changes in

distance to sender

obstacles further away

Slow changes in the average power received (long term fading)

MULTIPLEXING

Multiplexing in 4 dimensions

space (si)

time (t)

frequency (f)

code (c)

Frequency Division Multiplexing - FDM

The oldest used technique used for multiplexing. Possible when the useful bandwidth of the medium exceeds that of the

signals it has to carry. Each signal is modulated on a different carrier frequency. This results in shifting the spectrum of

the signal around the carrier frequency. Sufficient guard-band is given so those neighboring signals do not overlap in the

frequency domain.

At the receiving end each signal is extracted by first passing it through a band-pass filter and then demodulating with the

same carrier frequency that was used to modulate the signal. The signals carried using FDM may be analog signals or may

be analog signals representing digital data. However FDM is mostly a technique from the era of analog communications.

In FDM a device uses some of the channel all of the time. FDM is used in radio and television broadcasting. FDM is also

used in high capacity long distance links in the telephone network.

Frequency division multiplexing (FDM) achieves multiplexing by using different carrier frequencies .Receiver can "tune"

to specific frequency and extract modulation for that one channel .Frequencies must be separated to avoid interference -

“Wastes” potential signal bandwidth for guard channels.Only useful in media that can carry multiple signals with different

frequencies - high-bandwidth required .

Used in:

The standard of the analog telephone network

The standard in radio broadcasting

The standard for video

1. Broadcast

2. Cable

3. Satellite

Frequency Division Multiplexing Diagram

Time Division Multiplexing - TDM

Time division multiplexing is more suitable for digital data. TDM can be used when the data rate available on a

communication link exceeds the data rate required by any one of the sources. In TDM each source that is to use the link

fills up a buffer with data. A TDM multiplexer scans the buffers in some predetermined order and transmits bits from

each source one after the other.

Requires digital signaling & transmission

Requires data rate = sum of inputs + framing

Data rate much higher than equivalent analog bandwidth uses

Separates data streams in time not frequency

The standard of the modern digital telephone system

Code Division Multiplexing - CDM

Each channel has a unique code. All channels use the same spectrum at the same time.

Advantages:

bandwidth efficient

no coordination and synchronization necessary

good protection against interference and tapping

Disadvantages:

lower user data rates

more complex signal regeneration

C

T

F

k2 k1 k3 k4 k5 k6

MODULATIONS

Digital modulation

o digital data is translated into an analog signal (baseband)

o ASK, FSK, PSK - main focus in this chapter

o differences in spectral efficiency, power efficiency, robustness

Analog modulation

o shifts center frequency of baseband signal up to the radio carrier Motivation

o smaller antennas (e.g., /4)

o Frequency Division Multiplexing

o medium characteristics

Basic schemes

o Amplitude Modulation (AM)

o Frequency Modulation (FM)

o Phase Modulation (PM)

Modulation and demodulation

Digital modulation

Modulation of digital signals known as Shift Keying.

Amplitude Shift Keying (ASK):

very simple

low bandwidth requirements

very susceptible to interference

Frequency Shift Keying (FSK):

needs larger bandwidth

Phase Shift Keying (PSK):

more complex

robust against interference

Advanced Frequency Shift Keying

bandwidth needed for FSK depends on the distance between the carrier frequencies

special pre-computation avoids sudden phase shifts

MSK (Minimum Shift Keying)

bit separated into even and odd bits, the duration of each bit is doubled

depending on the bit values (even, odd) the higher or lower frequency, original or inverted is chosen

the frequency of one carrier is twice the frequency of the other

even higher bandwidth efficiency using a Gaussian low-pass filter

GMSK (Gaussian MSK), used in GSM.

Advanced Phase Shift Keying

BPSK (Binary Phase Shift Keying):

bit value 0: sine wave

bit value 1: inverted sine wave

very simple PSK

low spectral efficiency

robust, used e.g. in satellite systems

QPSK (Quadrature Phase Shift Keying):

2 bits coded as one symbol

symbol determines shift of sine wave

needs less bandwidth compared to BPSK

more complex

Often also transmission of relative, not absolute phase shift: DQPSK - Differential QPSK (IS-136, PACS, PHS

BPSK (Binary Phase Shift Keying):

QPSK (Quadrature Phase Shift Keying):

Quadrature Amplitude Modulation

Quadrature Amplitude Modulation (QAM): combines amplitude and phase modulation

it is possible to code n bits using one symbol

2n discrete levels, n=2 identical to QPSK

bit error rate increases with n, but less errors compared to comparable PSK schemes

SPREAD SPECTRUM

Effects of spreading and interference

DSSS (Direct Sequence Spread Spectrum)

XOR of the signal with pseudo-random number (chipping sequence)

many chips per bit (e.g., 128) result in higher bandwidth of the signal

Advantages

reduces frequency selective fading

in cellular networks

o base station scan use the same frequency range several base stations can detect and recover the signal

o soft handover

Q

I

11

01

10

00

Q

I 0 1

Disadvantages

precise power control necessary

FHSS (Frequency Hopping Spread Spectrum)

Discrete changes of carrier frequency

sequence of frequency changes determined via pseudo random number sequence

Two versions

Fast Hopping:

several frequencies per user bit

Slow Hopping:

several user bits per frequency

Advantages

frequency selective fading and interference limited to short period

simple implementation

uses only small portion of spectrum at any time

Disadvantages

not as robust as DSSS

simpler to detect

FHSS (Frequency Hopping Spread Spectrum)

Frequency Hopping Spread Spectrum

Medium Access Control (MAC)

MAC protocol which were developed for nodes at short distance did not show good performance for nodes at longer

distance so another protocol has to be developed Known as 2p MAC Protocol.

802.11 protocols were good for devices which had no power supply issue frequent charging were available to them etc.

1. This protocol based devices were not good for certain operation like monitoring the natural habitat of wildlife.

2. Sampling the water level of dam.

These applications do not require frequent human intervention and are required to run for a longer duration.

To fulfill the requirement other protocol was developed sensor network (802.15.4)

Energy Budgets:-Main points which were discussed in this were how its protocol helps in saving power by

cleverly managing the time when device should sleep when to wake up.

MAC protocol used in 802.15.4.

Routing and tree formation in ZigBee: - Routing protocol was developed by Zigbee firm.

Wireless MAC Issues

Wireless medium makes the MAC design more challenging than the wireline networks.

The three important issues are:

1. Half Duplex operation –> either send or receive but not both at a given time

2. Time varying channel

3. Burst channel errors

1. Half Duplex Operation

In wireless, it’s difficult to receive data when the transmitter is sending the data, because:

When node is transmitting, a large fraction of the signal energy leaks into the receiver path

The transmitted and received power levels can differ by orders of magnitude

The leakage signal typically has much higher power than the received signal ->“Impossible to detect a

received signal, while transmitting data”

Collision detection is not possible, while sending data

As collision cannot be detected by the sender, all proposed protocols attempt to minimize the probability of collision

-> Focus on collision avoidance

2. Time Varying Channel

Three mechanisms for radio signal propagation

Reflection – occurs when a propagating wave impinges upon an object that has very large dimensions than the

wavelength of the radio wave e.g. reflection occurs from the surface of the earth and from buildings and walls

Diffraction – occurs when the radio path between the transmitter and the receiver is obstructed by a surface

with sharp edges

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

The received signal by a node is a superposition of time-shifted and attenuated versions of the ransmitted signals the

received signal varies with time .The time varying signals (time varying channel) phenomenon also known as multipath

propagation. The rate of variation of channel is determined by the coherence time of the hannel Coherence time is defined

as time within which When a node’s received signal strength drops below a certain threshold the node is said to be in fade

.Handshaking is widely used strategy to ensure the link quality is good enough for data communication. A successful

handshake between a sender and a receiver (small message) indicates a good communication link.

3. Burst Channel Errors

As a consequence of time varying channel and varying signals strengths errors are introduced in the transmission (Very

likely) for wire line networks the bit error rate (BER) is the probability of packet error is small .For wire line networks the

errors are due to random For wireless networks the BER is as high.For wireless networks the errors are due to node being in

fade as a result errors occur in a long burst. Packet loss due to burst errors - mitigation techniques

» Smaller packets

» Forward Error Correcting Codes

» Retransmissions (Acks)

Location Dependent Carrier Sensing

Location Dependent Carrier Sensing results in three types of nodes that protocols need to deal with:

Hidden Nodes

Even if the medium is free near the transmitter, it may not be free near the intended receiver

Exposed Nodes

Even if the medium is busy near the transmitter, it may be free near the intended receiver

Capture

Capture occurs when a receiver can cleanly receive a transmission from one of two simultaneous transmissions

Hidden Node/Terminal Problem

A hidden node is one that is within the range of the intended destination but out of range of sender Node B can

communicate with A and C both A and C cannot hear each other When A transmits to B, C cannot detect the

transmission using the carrier sense mechanism C falsely thinks that the channel is idle

Exposed Nodes

An exposed node is one that is within the range of the sender but out of range of destination .when a node’s received signal

strength drops below a certain threshold the node is said to be in fade .Handshaking is widely used strategy to ensure the

link quality is good enough for data communication. A successful handshake between a sender and a receiver (small

message) indicates a good communication link.

In theory C can therefore have a parallel transmission with any node that cannot hear the transmission from B, i.e. out

of range of B. But C will not transmit to any node because it’s an exposed node. Exposed nodes waste bandwidth.

Capture

Capture is said to occur when a receiver can cleanly receive a transmission from one of two simultaneous transmissions both

within its range Assume node A and D transmit simultaneously to B. The signal strength received from D is much higher

than that from A, and D’s transmission can be decoded without errors in presence of transmissions from A.D has captured A.

Capture is unfair because it gives preference to nodes that are closer to the receiver. It may improve protocol performance

MULTIPLE ACCESS

FDMA

It is an ANALOQUE technique in time. Synchronization the transmission bandwidth is partitioned to frequency slots

different users has different RF carrier frequencies, i.e. Each user is assigned a particular frequency slot.

users/signals are at the receiver by separated out FILTERING if all frequency slots are occupied then the system has

reached its.

TDMA

It is a DIGITAL technique requires between users synchronization each user/signal is assigned a particular (within

a time-frame) time slot.

CELLULAR WIRELESS NETWORKS

Implements space division multiplex: base station covers a certain transmission area (cell).Mobile stations communicate

only via the base station

Advantages of cell structures:

higher capacity, higher number of users

less transmission power needed

more robust, decentralized

base station deals with interference, transmission area etc. locally

Problems:

fixed network needed for the base stations

handover (changing from one cell to another) necessary

interference with other cells

Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM) - even less for higher frequencies

Frequency reuse only with a certain distance between the base stations

Standard model using 7 frequencies:

Fixed frequency assignment:

certain frequencies are assigned to a certain cell

problem: different traffic load in different cells

Dynamic frequency assignment:

base station chooses frequencies depending on the frequencies already used in neighbor cells

more capacity in cells with more traffic

assignment can also be based on interference measurements

3 cell cluster 3 cell cluster with 3 sector antennas

f4 f5

f1 f3

f2

f6

f7

f3 f2

f4 f5

f1

Cell : Why Hexagon?

• In reality the cell is an irregular shaped circle, for design convenience and as a first order approximation, it is

assumed to be regular polygons

• The hexagon is used for two reasons:

– A hexagonal layout requires fewer cells, therefore, fewer transmission site

– Less expensive compared to square and triangular cells

• Irregular cell shape leads to inefficient use of the spectrum because of inability to reuse frequency on account of

co channel interference uneconomical deployment of equipment, requiring relocation from one cell site to

another

UNIT I WIRELESS COMMUNICATION FUNDAMENTALS

Part- A

1. Define SAMA.

Spread Aloha Multiple Access is a combination of CDMA and TDMA. The

CDMA better suits for connection oriented services only and not for connection less

bursty data traffic because it requires to program both sender and receiver to access

different users with different codes.

2. Define CDMA.

Code Division Multiple Access systems use codes with certain characteristics to separate

different users. To enable access to the shared medium without interference. The users

use the same frequency and time to transmit data. The main problem is to find good

codes and to separate this signal from noise. The good code can be found the following 2

characteristic 1.Orthogonal, 2.AutoCorrelation.

3. What are the several versions in CSMA?

There are several versions in CSMA, they are as follows

a) Non-persistent CSMA

b) p-persistent CSMA

c) 1-persistent CSMA

4. What is meant by non-persistent CSMA?

In, non-persistent CSMA, stations sense the carrier and start sending immediately

if the medium is idle., if the medium is busy, the station pauses a random amount of time

before sensing the medium again and repeating this pattern.

5. What is meant by p-persistent CSMA?

In p-persistent CSMA system nodes also sense the medium, but only transmit with a

probability of p. With the station deferring to the next slot with the probability 1-p,

i.e. access is slotted in addition.

6. What is SDMA?

Space Division Multiple Access (SDMA) is used for allocating separated spaces to users

in wireless networks. The basis for the SDMA algorithm is formed by cells and

sectorized antennas which constitute the infrastructure implementing space division

multiplexing (SDM)

7. What is FDD?

In FDMA, the base station and the mobile station establish a duplex channel. The two

directions, mobile station to base station and vice versa are separated using different

frequencies. This Scheme is called Frequency Division Duplex (FDD)

8. What are the 2 sub layers in DLC?

Logical Link Control (LLC)

Media Access Control (MAC)

9. List out the advantages of frequency division multiplexing.

no dynamic coordination necessary

works also for analog signals

10. List out the disadvantages of frequency division multiplexing.

waste of bandwidth if the traffic is distributed unevenly

inflexible

guard spaces

11. Define time division multiplexing.

A channel gets the whole spectrum for a certain amount of time

12. List out the advantages of time division multiplexing.

only one carrier in the

medium at any time

throughput high even

for many users

13. List out the disadvantages of time division multiplexing.

precise

synchronization

necessary

14. Define code division multiplexing.

Each channel has a unique code

All channels use the same spectrum at the same time

15. Define Signal

physical representation of data

function of time and location

signal parameters: parameters representing the value of data

16. Define Analog modulation.

shifts center frequency of base band signal up to the radio carrier

17. What is Quadrature Amplitude Modulation? Quadrature Amplitude Modulation (QAM): combines amplitude and phase modulation

it is possible to code n bits using one symbol

2n discrete levels, n=2 identical to QPSK

bit error rate increases with n, but less errors compared to comparable PSK schemes

18. What is digital modulation?

* Digital data is translated into an analog signal (baseband)

* ASK, FSK, PSK - main focus in this chapter

* Differences in spectral efficiency, power efficiency, robustness

UNIT1 - WIRELESS COMMUNICATION FUNDAMENTALS

Part B

1. Explain different TDMA schemes in detail.

Fixed TDMA, Classical TDMA, Slotted TDMA, Carrier sense multiple access, Demand

assigned multiple access, PRMA Packet reservation multiple access, Reservation multiple

access, Reservation TDMA, Multiple access with collision avoidance, Polling, Inhibit sense

multiple access.

2. Explain multiplexing in detail.

Frequency multiplex

Time multiplex

Code multiplex

3. Discuss Modulation techniques in detail.

Digital modulation

Analog modulation

Basic schemes

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation (PM)

4. Account on CDMA Scheme.

Good code, Orthogonal, Autocorrelation, Spread aloha multiple access.

5. Explain FDMA in detail

Segment the frequency band into

Disjoint sub-bands.

Terminals

Signal

Separation

Advantages

Disadvantages

6. Discuss SDMA in detail

segment space into cells/sectors

Terminals

Signal

Separation

Advantages

Disadvantages

7.Explain major types of networks.

Satellite-based networks

Cellular networks

Cordless systems

Fixed wireless access schemes

8. Explain types of Antennas in detail.

Isotropic antenna (idealized)

Radiates power equally in all directions

Dipole antennas

WhtHalf-wave dipole antenna (or Hertz antenna)

Quarter-wave vertical antenna (or Marconi antenna)

Parabolic Reflective Antenna

9. Explain the various applications of mobile computing.

Various applications and explanation

1

IT1402 -MOBILE COMPUTING

UNIT II

TELECOMMUNICATION NETWORKS

Telecommunication systems – GSM – GPRS – DECT – UMTS – IMT-2000 – Satellite Networks - Basics –

Parameters and Configurations – Capacity Allocation – FAMA and DAMA – Broadcast Systems – DAB - DVB.

Telecommunication systems -GSM – GPRS – DECT – UMTS – IMT-2000

Building Blocks

• AMPS – Advanced Mobile Phone System

• TACS – Total Access Communication System

• NMT – Nordic Mobile Telephone System

AMPS – Advanced Mobile Phone System

• analog technology

• used in North and South America and approximately 35 other countries

• operates in the 800 MHz band using FDMA technology

TACS – Total Access Communication System

• variant of AMPS

• deployed in a number of countries

• primarily in the UK

NMT – Nordic Mobile Telephone System

• analog technology

• deployed in the Benelux countries and Russia

• operates in the 450 and 900 MHz band

• first technology to offer international roaming – only within the Nordic countries

2

System Architecture

Mobile Station (MS)

Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Base Station Subsystem (BBS)

Base Transceiver Station (BTS)

Base Station Controller (BSC)

Network Subsystem

Mobile Switching Center (MSC)

Home Location Register (HLR)

Visitor Location Register (VLR)

Authentication Center (AUC)

Equipment Identity Register (EIR)

• Mobile Station: is a subscriber unit intended for use while on the move at unspecified locations. It could be a

hand-held or a portable terminal.

• Base Station: a fixed radio station used for communication with MS. It is located at the centre of a cell and

consist of Transmitters and Receivers.

• Mobile Switching Centre: it coordinates the routing of calls, do the billing, etc.

Mobile Station (MS)

The Mobile Station is made up of two entities:

1. Mobile Equipment (ME)

2. Subscriber Identity Module (SIM)

Mobile Equipment

• Produced by many different manufacturers

• Must obtain approval from the standardization body

• Uniquely identified by an IMEI (International Mobile Equipment Identity)

Base Transceiver Station (BTS)

Base Transceiver Station

(BTS)

Base Station Controller

(BSC)

Abis interface Base Station (BS)

Base Transceiver Station

(BTS)

Base Transceiver Station

(BTS)

Base Station Controller

(BSC)

Mobile Stations (MS)

Um interface

A interface

Base Station (BS)

Abis interface

CCITT Signalling

System No. 7 (SS7)

interface

Mobile Switchin

g Centre (MSC)

GMSC

PSTN

VLR

HLR

3

Subscriber Identity Module (SIM)

• Smart card containing the International Mobile Subscriber Identity (IMSI)

• Allows user to send and receive calls and receive other subscribed services

• Encoded network identification details

• Protected by a password or PIN

• Can be moved from phone to phone – contains key information to activate the phone

Base Station Subsystem (BBS)

Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing

operation between components made by different suppliers

1. Base Transceiver Station (BTS)

1. Base Station Controller (BSC)

Base Transceiver Station (BTS)

• Houses the radio transceivers that define a cell

• Handles radio-link protocols with the Mobile Station

• Speech and data transmissions from the MS are recoded

• Requirements for BTS:

o ruggedness

o reliability

o portability

o minimum costs

Base Station Controller (BSC)

• Manages Resources for BTS

• Handles call set up

• Location update

• Handover for each MS

Network Subsystem

Mobile Switching Center (MSC)

• Switch speech and data connections between:

Base Station Controllers

Mobile Switching Centers

GSM-networks

Other external networks

• Heart of the network

• Three main jobs:

1) Connects calls from sender to receiver

2) Collects details of the calls made and received

3) Supervises operation of the rest of the network components

Home Location Registers (HLR)

- contains administrative information of each subscriber

- Current location of the mobile

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Visitor Location Registers (VLR)

- contains selected administrative information from the HLR

- authenticates the user

- tracks which customers have the phone on and ready to receive a call

- periodically updates the database on which phones are turned on and ready to receive calls

Authentication Center (AUC)

- mainly used for security

- data storage location and functional part of the network

- Ki is the primary element

Equipment Identity Register (EIR)

Database that is used to track handsets using the IMEI (International Mobile

Equipment Identity)

- Made up of three sub-classes: The White List, The Black List and the Gray List

- Optional database

Basic Features Provided by GSM

• Call Waiting

- Notification of an incoming call while on the handset

• Call Hold

- Put a caller on hold to take another call

• Call Barring

- All calls, outgoing calls, or incoming calls

• Call Forwarding

- Calls can be sent to various numbers defined by the user

• Multi Party Call Conferencing

- Link multiple calls together

Advanced Features Provided by GSM

• Calling Line ID

- incoming telephone number displayed

• Alternate Line Service

- one for personal calls

- one for business calls

• Closed User Group

- call by dialing last for numbers

• Advice of Charge

- tally of actual costs of phone calls

• Fax & Data

- Virtual Office / Professional Office

• Roaming

- services and features can follow customer from market to market

Advantages of GSM

• Crisper, cleaner quieter calls

• Security against fraud and eavesdropping

• International roaming capability in over 100 countries

• Improved battery life

• Efficient network design for less expensive system expansion

• Efficient use of spectrum

• Advanced features such as short messaging and caller ID

5

• A wide variety of handsets and accessories

• High stability mobile fax and data at up to 9600 baud

• Ease of use with over the air activation, and all account information is held in a smart card which can be

moved from handset to handset

UMTS (Universal Mobile Telephone System

• Reasons for innovations

- new service requirements

- availability of new radio bands

• User demands

- seamless Internet-Intranet access

- wide range of available services

- compact, lightweight and affordable terminals

- simple terminal operation

- open, understandable pricing structures for the whole spectrum of available services

UMTS Basic Parameter

• Frequency Bands (FDD : 2x60 MHz):

– 1920 to 1980 MHz (Uplink)

– 2110 to 2170 MHz (Downlink)

• Frequency Bands (TDD: 20 + 15 MHz):

– 1900 – 1920 MHz and 2010 – 2025 MHz

• RF Carrier Spacing:

– 4.4 - 5 MHz

• RF Channel Raster:

– 200 KHz

• Power Control Rate:

– 1500 Cycles per Second

UMTS W-CDMA Architecture

6

GPRS

General Packet Radio Service

Definition:

GPRS stands for General Packet Radio Service and is a second generation (2G) and third generation (3G)--

or sometimes refered to as in-between both generations, 2.5G--wireless data service that extends GSM data

capabilities for Internet access, multimedia messaging services, and early mobile Internet applications via

the wireless application protocol (WAP), as well as other wireless data services.

Features of GPRS

GPRS was one of the earliest cell phone data access technologies, and more widespread particularly in

Europe and Asia, though it was adopted by carriers in North America, such as Rogers in Canada and T-

Mobile in the US.

2G (second generation) GPRS service had data rates of 56-114 kbit/second--akin to dial-up modem speeds.

GPRS wireless networks were later enhance faster 3G (third generation) throughput speeds. T-Mobile's

EDGE (enhanced Data Rates for Global Evolution), for example, delivers up to 4 times the GPRS rate.

Both GPRS and Edge, however, are quickly being surpassed by even faster 4G (fourth generation) mobile

data networks.

Examples:

GPRS, which refers to a mobile or wireless data service, is not the same as GPS, which refers to geo-

location. GPRS data networks enable users to access Web data and rich content from their cell phones.

Technical overview

The GPRS core network allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external

networks such as the Internet. The GPRS system is an integrated part of the GSM network switching

subsystem.

Services offered

GPRS extends the GSM Packet circuit switched data capabilities and makes the following services possible:

SMS messaging and broadcasting

"Always on" internet access

Multimedia messaging service (MMS)

Push to talk over cellular (PoC)

Instant messaging and presence—wireless village

Internet applications for smart devices through wireless application protocol (WAP)

Point-to-point (P2P) service: inter-networking with the Internet (IP)

Point-to-Multipoint (P2M) service: point-to-multipoint multicast and point-to-multipoint group calls

7

If SMS over GPRS is used, an SMS transmission speed of about 30 SMS messages per minute may be

achieved. This is much faster than using the ordinary SMS over GSM, whose SMS transmission speed is

about 6 to 10 SMS messages per minute.

Protocols supported

GPRS supports the following protocols:

Internet protocol IP. In practice, built-in mobile browsers use IPv4 since IPv6 was not yet popular.

Point-to-point protocol (PPP). In this mode PPP is often not supported by the mobile phone operator

but if the mobile is used as a modem to the connected computer, PPP is used to tunnel IP to the

phone. This allows an IP address to be assigned dynamically (IPCP not DHCP) to the mobile

equipment.

X.25 connections. This is typically used for applications like wireless payment terminals, although it

has been removed from the standard. X.25 can still be supported over PPP, or even over IP, but

doing this requires either a network based router to perform encapsulation or intelligence built in to

the end-device/terminal; e.g., user equipment (UE).

When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will store and

forward the IP packets to the phone even during handover. The TCP handles any packet loss (e.g. due to a

radio noise induced pause).

Hardware

Devices supporting GPRS are divided into three classes:

Class A

Can be connected to GPRS service and GSM service (voice, SMS), using both at the same time.

Such devices are known to be available today.

Class B

Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at

a given time. During GSM service (voice call or SMS), GPRS service is suspended, and then

resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS

mobile devices are Class B.

Class C

Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually

between one or the other service.

A true Class A device may be required to transmit on two different frequencies at the same time, and thus

will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual

transfer mode (DTM) feature. A DTM-capable mobile may use simultaneous voice and packet data, with

the network coordinating to ensure that it is not required to transmit on two different frequencies at the same

time. Such mobiles are considered pseudo-Class A, sometimes referred to as "simple class A". Some

networks support DTM since 2007

8

DECT

Digital Enhanced Cordless Telecommunications

The base unit and handset of a British Telecom DECT cordless telephone

Digital Enhanced Cordless Telecommunications (Digital European Cordless Telecommunications), usually known by

the acronym DECT, is a digital communication standard, which is primarily used for creating cordless phone systems.

It originated in Europe, where it is the universal standard, replacing earlier cordless phone standards, such as

900 MHz CT1 and CT2.

Beyond Europe, it has been adopted by Australia, and most countries in Asia and South America. North American

adoption was delayed by United States radio frequency regulations. This forced development of a variation of DECT,

called DECT 6.0, using a slightly different frequency range; the technology is nearly identical, but the frequency

difference makes the technology incompatible with systems in other areas, even from the same manufacturer. DECT

has almost universally replaced other standards in most countries where it is used, with the exception of North

America.

DECT is used primarily in home and small office systems, but is also available in many PBX systems for medium and

large businesses. DECT can also be used for purposes other than cordless phones. Voice applications, such as baby

monitors, are becoming common. Data applications also exist, but have been eclipsed by Wi-Fi. 3G cellular also

competes with both DECT and Wi-Fi for both voice and data. Nowadays you can find DECT as well in special

applications like Remote Controls for industrial applications.

DECT handsets and bases from different manufacturers typically work together at the most basic level of

functionality: making and receiving calls. The DECT standard includes a standardized interoperability profile for

simple telephone capabilities, called GAP, which most manufacturers implement. The standard also contains several

other interoperability profiles, for data and for radio local-loop services.

Application

The DECT standard fully specifies a means for a portable unit, such as a cordless telephone, to access a fixed

telecoms network via radio. But, unlike the GSM standards, does not specify any internal aspects of the fixed network

itself. Connectivity to the fixed network (which may be of many different kinds) is done through a base station or

"Radio Fixed Part" to terminate the radio link, and a gateway to connect calls to the fixed network. In most cases the

gateway connection is to the public switched telephone network or telephone jack, although connectivity with newer

technologies such as Voice over IP has become available. There are also other devices such as some baby monitors

utilizing DECT, and in these devices there is no gateway functionality. The DECT standard originally envisaged three

major areas of application:

Domestic cordless telephony, using a single base station to connect one or more handsets to the public

telecoms network.

Enterprise premises cordless PABXs and wireless LANs, using many base stations for coverage. Calls

continue as users move between different coverage cells, through a mechanism called handover. Calls can be

both within the system and to the public telecoms network.

Public access, using large numbers of base stations to provide high capacity building or urban area coverage

as part of a public telecoms network.

Of these, the domestic application (cordless home telephones) has been extremely successful. The enterprise PABX

market had some success, and all the major PABX vendors have offered DECT access options. The public access

application did not succeed, since public cellular networks rapidly out-competed DECT by coupling their ubiquitous

coverage with large increases in capacity and continuously falling costs. There has been only one major installation of

DECT for public access: in early 1998 Telecom Italia launched a DECT network known as "Fido" after much

9

regulatory delay, covering major cities in Italy. The service was promoted for only a few months and, having peaked

at 142,000 subscribers, was shut down in 2001.

DECT has also been used for Fixed Wireless Access as a substitute for copper pairs in the "last mile" in countries

such as India and South Africa. By using directional antennas and sacrificing some traffic capacity, cell coverage

could extend to over 10 km. In Europe the power limit laid down for use of the DECT spectrum (250 mW peak) was

expressed in ERP, rather than the more commonly-used EIRP, permitting the use of high-gain directional antennas to

produce much higher EIRP and hence long ranges.

The standard is also used in electronic cash terminals, traffic lights, and remote door openers.

Features

Typical abilities of a domestic DECT Generic Access Profile (GAP) system include:

Multiple handsets to one base station and one phone line socket. This allows several cordless telephones to be

placed around the house, all operating from the same telephone jack. Additional handsets have a battery

charger station which does not plug into the telephone system. Handsets can in many cases be used as

intercoms, communicating between each other, and sometimes as walkie-talkies, intercommunicating without

telephone line connection.

Interference-free wireless operation to around 100 metres (109 yards) outdoors, much less indoors when

separated by walls. Operates clearly in common congested domestic radio traffic situations, for instance,

generally immune to interference from other DECT systems, Wi-Fi networks, video senders, Bluetooth

technology, baby monitors and other wireless devices.

Talk-time of several hours and standby time of several days on one battery charge.

Some systems offer:

A longer range between the telephone and base station (usable further from the base)

Extended battery talk-time, sometimes up to 24 hours

Technical properties

Some DECT properties:

Audio codec: G.726, G.711, G.722 (wideband), G.729.1 (wideband) and MPEG-4 ER LD AAC (wideband

and super-wideband)

Net bit rate: 32 kbit/s

Frequency: 1880 MHz–1900 MHz in Europe, 1900 MHz-1920 MHz in China,1893 MHz–1906 MHz in

Japan, 1910 MHz-1930 MHz in Latin America and 1920 MHz–1930 MHz in the US and Canada, US DECT

and DECT 6 products may NOT be used in the UK or Ireland as they cause and suffer from interference with

the UK & Ireland 3G cellular networks with unlicensed use of such products being prohibited by UK

agencies. As DECT and DECT 6.0 do not operate in the 2.4 GHz ISM band, they are not subject to the

interference arising in this band from its use by 802.11b and 802.11g WiFi, and 2.4 GHz cordless phones.

Carriers: 10 (1.728 MHz spacing) in Europe, 5 (1.728 MHz spacing) in the US

Time slots: 2 x 12 (up and down stream)

Channel allocation: dynamic

Average transmission power: 10 mW (250 mW peak) in Europe, 4 mW (100 mW peak) in the US

The DECT physical layer uses:

Frequency division multiple access (FDMA),

Time division multiple access (TDMA) and

Time division duplex (TDD)

10

This means that the radio spectrum is divided into physical channels in two dimensions: frequency and time.

The maximum allowed power for portable equipment as well as base stations is 250 mW. A portable device radiates

an average of about 10 mW during a call as it is only using one of 24 time slots to transmit.

The DECT media access control layer controls the physical layer and provides connection oriented, connectionless

and broadcast services to the higher layers.

The DECT data link layer uses LAPC (Link Access Protocol Control), a specially designed variant of the ISDN data

link protocol called LAPD. They are based on HDLC.

The DECT network layer always contains the following protocol entities:

Call Control (CC)

Mobility Management (MM)

Optionally it may also contain others:

Call Independent Supplementary Services (CISS)

Connection Oriented Message Service (COMS)

Connectionless Message Service (CLMS)

All these communicate through a Link Control Entity (LCE).

The call control protocol is derived from ISDN DSS1, which is a Q.931 derived protocol. Many DECT-specific

changes have been made. The mobility management protocol includes many elements similar to the GSM protocol,

but also includes elements unique to DECT.

Unlike the GSM protocol, the DECT network specifications do not define cross-linkages between the operation of the

entities (for example, Mobility Management and Call Control). The architecture presumes that such linkages will be

designed into the interworking unit that connects the DECT access network to whatever mobility-enabled fixed

network is involved. By keeping the entities separate, the handset is capable of responding to any combination of

entity traffic, and this creates great flexibility in fixed network design without breaking full interoperability.

DECT GAP is an interoperability profile for DECT. The intent is that two different products from different

manufacturers that both conform not only to the DECT standard, but also to the GAP profile defined within the DECT

standard, are able to interoperate for basic calling. The DECT standard includes full testing suites for GAP, and GAP

products on the market from different manufacturers are in practice interoperable for the basic functions.

Security

The DECT media access control layer also provides encryption services with the DECT Standard Cipher (DSC). The

encryption is fairly weak, using a 35-bit initialization vector and encrypting the voice stream with 64-bit encryption.

The security algorithm has been broken. Another attack involves impersonating a DECT base station, which allows

calls to be listened to, recorded, and re-routed to a different destination.

11

International Mobile Telecommunications (IMT)

IMT 2000, also known as International Mobile Telecommunications 2000, is the ITU globally coordinated

definition of 3G covering key issues such as frequency spectrum use and technical standards.

Different types of 3G Networks specified by IMT 2000

ITU Recommendation ITU-R M.1457 specifies five types of 3G radio interfaces:

IMT-2000 CDMA Direct Spread, also known as UTRA FDD including WCDMA in Japan,

ARIB / DoCoMo recommendation. UMTS is developed by 3GPP.

IMT-2000 CDMA Multi-carrier, also known as Cdma2000 (3X) developed by 3GPP2. IMT-

2000 CDMA2000 includes 1X components, like cdma2000 1X EV-DO.

IMT-2000 CDMA TDD, also known as UTRA TDD and TD-SCDMA. TD-SCDMA is

developed in China and supported by TD-SCDMA Forum.

IMT-2000 TDMA Single Carrier, also known as UWC-136 (Edge) supported by UWCC.

IMT-2000 DECT supported by DECT Forum.

Features

Data rates

ITU has not provided a clear definition of the data rate users can expect from 3G equipment or providers.

Thus users sold 3G service may not be able to point to a standard and say that the rates it specifies are not

being met. While stating in commentary that "it is expected that IMT-2000 will provide higher transmission

rates: a minimum data rate of 2 Mbit/s for stationary or walking users, and 384 kbit/s in a moving vehicle,

the ITU does not actually clearly specify minimum or average rates or what modes of the interfaces qualify

as 3G, so various rates are sold as 3G intended to meet customers expectations of broadband data.

Security

3G networks offer greater security than their 2G predecessors. By allowing the UE (User Equipment) to

authenticate the network it is attaching to, the user can be sure the network is the intended one and not an

impersonator. 3G networks use the KASUMI block cipher instead of the older A5/1 stream cipher.

However, a number of serious weaknesses in the KASUMI cipher have been identified.

In addition to the 3G network infrastructure security, end-to-end security is offered when application

frameworks such as IMS are accessed, although this is not strictly a 3G property.

Applications of 3G

The bandwidth and location information available to 3G devices gives rise to applications not previously

available to mobile phone users. Some of the applications are:

Mobile TV

Video on demand

Video Conferencing

Telemedicine

Location-based services

Global Positioning System (GPS)

12

SATELLITE NETWORKS

History of satellite communication

1945 Arthur C. Clarke publishes an essay about „Extra

Terrestrial Relays“

1957 first satellite SPUTNIK

1960 first reflecting communication satellite ECHO

1963 first geostationary satellite SYNCOM

1965 first commercial geostationary satellite Satellit „Early Bird“

(INTELSAT I): 240 duplex telephone channels or 1 TV

channel, 1.5 years lifetime

1976 three MARISAT satellites for maritime communication

1982 first mobile satellite telephone system INMARSAT-A

1988 first satellite system for mobile phones and data

communication INMARSAT-C

1993 first digital satellite telephone system

1998 global satellite systems for small mobile phones

Applications

� Traditionally

� weather satellites

� radio and TV broadcast satellites

� military satellites

� satellites for navigation and localization (e.g., GPS)

� Telecommunication

� global telephone connections

� backbone for global networks

� connections for communication in remote places or underdeveloped areas

� global mobile communication

� satellite systems to extend cellular phone systems (e.g., GSM orAMPS)

Classical satellite systems

Basics

Satellites in circular orbits

� attractive force Fg = m g (R/r)²

� centrifugal force Fc = m r ω²

� m: mass of the satellite

� R: radius of the earth (R = 6370 km)

� r: distance to the center of the earth

� g: acceleration of gravity (g = 9.81 m/s²)

� ω: angular velocity (ω = 2 π f, f: rotation frequency)

13

Stable orbit

Fg = Fc

Basics

o Elliptical or circular orbits

o Complete rotation time depends on distance satellite-earth

o Inclination: angle between orbit and equator

o Elevation: angle between satellite and horizon

o LOS (Line of Sight) to the satellite necessary for connection

1. High elevation needed, less absorption due to e.g. buildings

o Uplink: connection base station - satellite

o Downlink: connection satellite - base station

o Typically separated frequencies for uplink and downlink

1. Transponder used for sending/receiving and shifting of frequencies

2. Transparent transponder: only shift of frequencies

3. Regenerative transponder: additionally signal regeneration

IElevation

Link budget of satellites

Parameters like attenuation or received power determined by four parameters:

Sending power

Gain of sending antenna

Distance between sender and receiver

Gain of receiving antenna Problems

Varying strength of received signal due to multipath propagation

Interruptions due to shadowing of signal (no LOS) possible solutions

Link Margin to eliminate variations in signal strength

Satellite diversity (usage of several visible satellites at the same time) helps to use less sending power

14

L: Loss

f: carrier frequency

r: distance

c: speed of light

ORBITS

Four different types of satellite orbits can be identified depending on the shape and diameter of the orbit:

� GEO: geostationary orbit, ca. 36000 km above earth surface

� LEO (Low Earth Orbit): ca. 500 - 1500 km

� MEO (Medium Earth Orbit) or ICO (Intermediate Circular Orbit):

ca. 6000 - 20000 km

� HEO (Highly Elliptical Orbit) elliptical orbits

Geostationary satellites

Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°)

Complete rotation exactly one day, satellite is synchronous to earth rotation

Fix antenna positions, no adjusting necessary

Satellites typically have a large footprint (up to 34% of earth surface!), therefore difficult to reuse frequencies

Bad elevations in areas with latitude above 60° due to fixed position above the equator

High transmit power needed

High latency due to long distance (ca. 275 ms)

Not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV

transmission

LEO systems

Orbit ca. 500 - 1500 km above earth surface

Visibility of a satellite ca. 10 - 40 minutes

Global radio coverage possible

Latency comparable with terrestrial long distance

Connections, ca. 5 - 10 ms

Smaller footprints, better frequency reuse

But now handover necessary from one satellite to another

Many satellites necessary for global coverage

More complex systems due to moving satellites

Examples:

Iridium (start 1998, 66 satellites)

Global star (start 1999, 48 satellites)

15

MEO systems

Orbit ca. 5000 - 12000 km above earth surface

Comparison with LEO systems:

Slower moving satellites

Less satellites needed

Simpler system design

For many connections no hand-over needed

Higher latency, ca. 70 - 80 ms

Higher sending power needed

Special antennas for small footprints needed

Example:

ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000

Routing

One solution: inter satellite links (ISL)

Reduced number of gateways needed

Forward connections or data packets within the satellite network as long as possible

Only one uplink and one downlink per direction needed for the connection of two mobile phones

Problems:

More complex focusing of antennas between satellites

High system complexity due to moving routers

Higher fuel consumption

Thus shorter lifetime

Iridium and Teledesic planned with ISL

Other systems use gateways and additionally terrestrial networks

Localization of mobile stations

Mechanisms similar to GSM

Gateways maintain registers with user data

HLR (Home Location Register): static user data

VLR (Visitor Location Register): (last known) location of the mobile station

SUMR (Satellite User Mapping Register):

Satellite assigned to a mobile station

Positions of all satellites

Registration of mobile stations

Localization of the mobile station via the satellite’s position

Requesting user data from HLR

Updating VLR and SUMR

Calling a mobile station

Localization using HLR/VLR similar to GSM

Connection setup using the appropriate satellite

Handover in satellite systems

Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks

caused by the movement of the satellites

Intra satellite handover

Handover from one spot beam to another

Mobile station still in the footprint of the satellite, but in another cell

Inter satellite handover

Handover from one satellite to another satellite

Mobile station leaves the footprint of one satellite

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Gateway handover

Handover from one gateway to another

Mobile station still in the footprint of a satellite, but gateway leaves the footprint

Inter system handover

Handover from the satellite network to a terrestrial cellular network

Mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.

Overview of LEO/MEO systems

FDMA - Frequency Division Multiple Access

Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a

channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. It

is particularly commonplace in satellite communication. FDMA, like other Multiple Access systems, coordinates

access between multiple users. Alternatives include TDMA, CDMA, or SDMA. These protocols are utilized

differently, at different levels of the theoretical OSI model.

Disadvantage: Crosstalk may cause interference among frequencies and disrupt the transmission.

Features

In FDMA all users share the satellite simultaneously but each user transmits at single frequency.

FDMA can be used with both analog and digital signal.

FDMA requires high-performing filters in the radio hardware, in contrast to TDMA and CDMA.

FDMA is not vulnerable to the timing problems that TDMA has. Since a predetermined frequency

band is available for the entire period of communication, stream data (a continuous flow of data that

may not be packetized) can easily be used with FDMA.

Due to the frequency filtering, FDMA is not sensitive to near-far problem which is pronounced for

CDMA.

Each user transmits and receives at different frequencies as each user gets a unique frequency slot

17

FDMA is distinct from frequency division duplexing (FDD). While FDMA allows multiple users simultaneous access

to a transmission system, FDD refers to how the radio channel is shared between the uplink and downlink (for

instance, the traffic going back and forth between a mobile-phone and a mobile phone base station). Frequency-

division multiplexing (FDM) is also distinct from FDMA. FDM is a physical layer technique that combines and

transmits low-bandwidth channels through a high-bandwidth channel. FDMA, on the other hand, is an access method

in the data link layer.

FDMA also supports demand assignment in addition to fixed assignment. Demand assignment allows all users

apparently continuous access of the radio spectrum by assigning carrier frequencies on a temporary basis using a

statistical assignment process. The first FDMA demand-assignment system for satellite was developed by COMSAT

for use on the Intelsat series IVA and V satellites.

There are two main techniques:

Multi-channel per-carrier (MCPC)

Single-channel per-carrier (SCPC)

Hints

Satellite frequency is already broken into bands, and is broken in to smaller channels in

Frequency Division Multiple Access (FDMA).

Overall bandwidth within a frequency band is increased due to frequency reuse (a frequency is

used by two carriers with orthogonal polarization).

The number of sub-channels is limited by three factors:

o Thermal noise (too weak a signal will be effected by background noise).

o Intermodulation noise (too strong a signal will cause noise).

o Crosstalk (cause by excessive frequency reusing).

FDMA can be performed in two ways:

o Fixed-assignment multiple access (FAMA): The sub-channel assignments are of a

fixed allotment. Ideal for broadcast satellite communication.

o Demand-assignment multiple access (DAMA): The sub-channel allotment changes

based on demand. Ideal for point to point communication.

DAMA - Demand Assigned Multiple Access

Demand Assigned Multiple Access (DAMA) is a technology used to assign a channel to clients that don't

need to use it constantly. DAMA systems assign communication channels based on requests issued from

user terminals to a network control system. When the circuit is no longer in use, the channels are then

returned to the central pool for reassignment to other users.

Channels are typically a pair of carrier frequencies (one for transmit and one for receive), but can be other

fixed bandwidth resources such as timeslots in a TDMA burst plan or even physical party line channels.

Once a channel is allocated to a given pair of nodes, it is not available to other users in the network until

their session is finished.

It allows utilizing of one channel (radio or baseband frequency, timeslot, etc.) by many users sequentially at

different times. This technology is mainly useful with sparsely used networks of transient clients, as opposed

to PAMA (Permanently Assigned Multiple Access). By using DAMA technology the number of separate

nodes that can use a limited pool of circuits can be greatly increased at the expense of no longer being able

18

to provide simultaneous access for all possible pairs of nodes. A five-channel DAMA network can only

have five simultaneous conversations but could have any number of nodes. A five-channel PAMA network

permanently supports five simultaneous conversations, with channel ownership remaining with their

permanently assigned nodes even when idle.

DAMA and PAMA are related only to channel/resource allocation and should not be confused with the

Multiple access/multiplexing methods (such as FDMA frequencies, TDMA slots, CDMA codes, or others)

intended to divide a single communication channel into multiple virtual channels. These systems typically

use resource allocation protocols that allow a more rapid (although often less deterministic, consider CDMA

collisions) near-real-time allocation of bandwidth based on demand and data priority. However, in sparsely

allocated multiple-access channels, DAMA can be used to allocate the individual virtual channel resources

provided by the multiple-access channel. This is most common in environments that are sufficiently

sparsely utilized that there is no need to add complexity just to recover "conversation gap" idle periods.

DAMA is widely used in satellite communications, especially in VSAT systems. It is very effective in

environments comprising multiple users each having a low to moderate usage profile.

DAMA is often used in military environments due to the relative simplicity of implementation, ease of

modeling, and the fact that military usage profiles are a very good fit. In military SATCOM, it has the added

advantage that it can function in a bent pipe environment, thus requires no special security or coordination

hardware on the satellite. This allows the master and slave ground stations to be upgraded repeatedly to

change or improve security and compression without requiring an expensive satellite replacement.

DAMA

Channel efficiency only 18% for Aloha, 36% for Slotted Aloha (assuming Poisson distribution for packet

arrival and packet length)

Reservation can increase efficiency to 80%

a sender reserves a future time-slot

sending within this reserved time-slot is possible without collision

reservation also causes higher delays

typical scheme for satellite links

Examples for reservation algorithms:

Explicit Reservation according to Roberts (Reservation-ALOHA)

Implicit Reservation (PRMA)

Reservation-TDMA

Access method DAMA: Explicit Reservation

Explicit Reservation (Reservation Aloha): Two modes:

ALOHA mode for reservation:

Competition for small reservation slots, collisions possible

reserved mode for data transmission in reserved slots (no collisions possible)

Important for all stations to keep the reservation list consistent. Thus all stations have to

synchronize periodically

19

Broadcasting Systems

Digital Audio Broadcasting

Digital Audio Broadcasting (DAB) is a digital radio technology for broadcasting radio stations, used in several

countries, particularly in Europe. As of 2006, approximately 1,002 stations worldwide broadcast in the DAB format.

The DAB standard was initiated as a European research project in the 1980s. The Norwegian Broadcasting

Corporation (NRK) launched the very first DAB channel in the world on June 1 1995 (NRK Klassisk), and the BBC

and SR launched their first DAB digital radio broadcasts in September 1995. DAB receivers have been available in

many countries since the end of the nineties. DAB may offer more radio programmes over a specific spectrum than

analogue FM radio. DAB is more robust with regard to noise and multipath fading for mobile listening, since DAB

reception quality first degrades rapidly when the signal strength falls below a critical threshold, whereas FM reception

quality degrades slowly with the decreasing signal.

An unblinded "informal listening test" by Sverre Holm has shown that for stationary listening the audio quality on

DAB is subjectively lower than FM stereo (but this may be due to observer bias). Most stations using a bit rate of 128

kbit/s or less, with the MP2 audio codec, which requires 160 kbit/s to achieve perceived FM quality. 128 kbit/s gives

better dynamic range or signal-to-noise ratio than FM radio, but a more smeared stereo image, and an upper cutoff

frequency of 14 kHz, corresponding to 15 kHz of FM radio.[5]

However, "CD sound quality" with MP2 is possible

"with 256..192 kbps".

An upgraded version of the system was released in February 2007, which is called DAB+. DAB is not forward

compatible with DAB+, which means that DAB-only receivers will not be able to receive DAB+ broadcasts.[7]

DAB+

is approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec, and DAB+ can provide

high quality audio with as low as 64 kbit/s. Reception quality will also be more robust on DAB+ than on DAB due to

the addition of Reed-Solomon error correction coding.

In spectrum management, the bands that are allocated for public DAB services, are abbreviated with T-DAB, where

the "T" stands for terrestrial.

More than 20 countries provide DAB transmissions, and several countries, such as Australia, Italy, Malta, Switzerland

and Germany, have started transmitting DAB+ stations. See Countries using DAB/DMB. However, DAB radio has

still not replaced the old FM system in popularity.

Benefits of DAB

Current AM and FM terrestrial broadcast technology is well established, compatible, and cheap to manufacture.

Benefits of DAB over analogue systems are explained below.

Improved features for users

DAB radios automatically tune to all the available stations, offering a list for the user to select from.

DAB can carry "radiotext" (in DAB terminology, Dynamic Label Segment, or DLS) from the station giving real-time

information such as song titles, music type and news or traffic updates. Advance programme guides can also be

transmitted. A similar feature also exists on FM in the form of the RDS. (However, not all FM receivers allow radio

stations to be stored by name.)

DAB receivers can display time of day as encoded into transmissions, so is automatically corrected when travelling

between time zones and when changing to or from Daylight Saving. This is not implemented on all receivers, and

some display time only when in "Standby" mode.

20

Some radios offer a pause facility on live broadcasts, caching the broadcast stream on local flash memory, although

this function is limited.

More stations

DAB is not more bandwidth efficient than analogue measured in programmes per MHz of a specific transmitter (the

so called link spectral efficiency). However, it is less susceptible to co-channel interference (cross talk), which makes

it possible to reduce the reuse distance, i.e. use the same radio frequency channel more densely. The system spectral

efficiency (the average number of radio programmes per MHz and transmitter) is a factor three more efficient than

analog FM for local radio stations, as can be seen in the above numerical example. For national and regional radio

networks, the efficiency is improved by more than an order of magnitude due to the use of SFNs. In that case,

adjacent transmitters use the same frequency.

In certain areas — particularly rural areas — the introduction of DAB gives radio listeners a greater choice of radio

stations. For instance, in South Norway, radio listeners experienced an increase in available stations from 6 to 21

when DAB was introduced in November 2006.

Reception quality

The DAB standard integrates features to reduce the negative consequences of multipath fading and signal noise,

which afflict existing analogue systems.

Also, as DAB transmits digital audio, there is no hiss with a weak signal, which can happen on FM. However, radios

in the fringe of a DAB signal, can experience a "bubbling mud" sound interrupting the audio and/or the audio cutting

out altogether.

Due to sensitivity to doppler shift in combination with multipath propagation, DAB reception range (but not audio

quality) is reduced when traveling speeds of more than 120 to 200 km/h, depending on carrier frequency.

Less pirate interference

The specialised nature and cost of DAB broadcasting equipment provide barriers to pirate radio stations broadcasting

on DAB. In cities such as London with large numbers of pirate radio stations broadcasting on FM, this means that

some stations can be reliably received via DAB in areas where they are regularly difficult or impossible to receive on

FM due to pirate radio interference.

Variable bandwidth

Mono talk radio, news and weather channels and other non-music programs need significantly less bandwidth than a

typical music radio station, which allows DAB to carry these programmes at lower bit rates, leaving more bandwidth

to be used for other programs.

However, this had led to the situation where some stations are being broadcast in mono

Transmission costs

It is common belief that DAB is more expensive to transmit than FM. It is true that DAB uses higher frequencies than

FM and therefore there is a need to compensate with more transmitters, higher radiated powers, or a combination, to

achieve the same coverage. A DAB network is also more expensive than an FM network. However, the last couple of

years have seen significant improvement in power efficiency for DAB-transmitters.

This efficiency originates from the ability a DAB network has in broadcasting more channels per network. One

network can broadcast 6-10 channels (with MPEG audio codec) or 10-16 channels (with HE AAC codec). Hence, it is

21

thought that the replacement of FM-radios and FM-transmitters with new DAB-radios and DAB-transmitters will not

cost any more as opposed to newer FM facilities.

Cheaper transmission costs is backed by independent network studies from Teracom (Sweden) and SSR/SRG

(Switzerland). Among other things they show that DAB is up to 6 times less expensive than FM.

Disadvantages of DAB

Reception quality

The reception quality on DAB can be poor even for people that live well within the coverage area. The reason for this

is that the old version of DAB uses weak error correction coding, so that when there are a lot of errors with the

received data not enough of the errors can be corrected and a "bubbling mud" sound occurs. In some cases a complete

loss of signal can happen. This situation will be improved upon in the new DAB standard (DAB+, discussed below)

that uses stronger error correction coding and as additional transmitters are built.

Audio Quality

Broadcasters have been criticized for ‘squeezing in’ more stations per ensemble than recommended, by:

Minimizing the bit-rate, to the lowest level of sound-quality that listeners are willing to tolerate, such as 128

kbit/s for stereo and even 64 kbit/s for mono speech radio.

Having few digital channels broadcasting in stereo.

Signal delay

The nature of a SFN is such that the transmitters in a network must broadcast the same signal at the same time. To

achieve synchronization, the broadcaster must counter any differences in propagation time incurred by the different

methods and distances involved in carrying the signal from the multiplexer to the different transmitters. This is done

by applying a delay to the incoming signal at the transmitter based on a timestamp generated at the multiplexer,

created taking into account the maximum likely propagation time, with a generous added margin for safety. Delays in

the receiver due to digital processing (e.g. deinterleaving) add to the overall delay perceived by the listener.[19]

The

signal is delayed by 2–4 seconds depending on the decoding circuitry used. This has disadvantages:

DAB radios are out of step with live events, so the experience of listening to live commentaries on events

being watched is impaired;

Delayed time signals : Even in a well-defined network with a fixed delay, the listener has to apply an offset

when using the broadcast time signal to set a clock.

Listeners using a combination of analog (AM or FM) and DAB radios (e.g. in different rooms of a house) will

hear a confusing mixture when both receivers are within earshot.

Coverage

As DAB is at a relatively early stage of deployment, DAB coverage is poor in nearly all countries in comparison to

the high population coverage provided by FM.

Compatibility

In 2006 tests began using the much improved HE-AAC codec for DAB+. Virtually none of the receivers made before

2008 support the new codec, however, thus making them partially obsolete once DAB+ broadcasts begin and

completely obsolete once the old MPEG-1 Layer 2 stations are switched off. However new receivers are both DAB

and DAB+ compatible.

22

Power requirements

As DAB requires digital signal processing techniques to convert from the received digitally encoded signal to the

analogue audio content, the complexity of the electronic circuitry required to do this is high. This translates into

needing more power to effect this conversion than compared to an analogue FM to audio conversion, meaning that

portable receiving equipment will tend to have a shorter battery life, or require higher power (and hence more bulk).

This means that they use more energy than analogue Band II VHF receivers.

As an indicator of this increased power consumption, some radio manufacturers quote the length of time their

receivers can play on a single charge. For a commonly used FM/DAB-receiver from manufacturer PURE, this is

stated as: DAB 10 hours, FM 22 hours.

Use of Licensed Codec

The use of MPEG and latterly AAC has prompted criticism of the fact that a (large) public system is financially

supporting a private company. In general, an open system will permit equipment to be bought from various sources in

competition with each other but by selecting a single vendor of codec, with which all equipment must be compatible,

this is not possible.

Digital Video Broadcasting

Digital Video Broadcasting (DVB) is a suite of internationally accepted open standards for digital television. DVB

standards are maintained by the DVB Project, an international industry consortium with more than 270 members, and

they are published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute

(ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union

(EBU). Many aspects of DVB are patented, including elements of the MPEG video coding and audio coding.

Transmission

DVB systems distribute data using a variety of approaches, including:

Satellite: DVB-S, DVB-S2 and DVB-SH

o DVB-SMATV for distribution via SMATV

Cable: DVB-C, DVB-C2

Terrestrial television: DVB-T, DVB-T2

o Digital terrestrial television for handhelds: DVB-H, DVB-SH

Microwave: using DTT (DVB-MT), the MMDS (DVB-MC), and/or MVDS standards (DVB-MS)

These standards define the physical layer and data link layer of the distribution system. Devices interact with the

physical layer via a synchronous parallel interface (SPI), synchronous serial interface (SSI), or asynchronous serial

interface (ASI). All data is transmitted in MPEG transport streams with some additional constraints (DVB-MPEG).

DVB has established a 3D TV group (CM-3DTV) to identify "what kind of 3D-TV solution does the market want and

need, and how can DVB play an active part in the creation of that solution?" The CM-3DTV group held a DVB 3D-

TV Kick-off Workshop in Geneva on January 25, 2010, followed by the first CM-3DTV meeting the next day.[3]

DVB

now defines a new standard for 3D video broadcast: DVB 3D-TV.

Content

Besides digital audio and digital video transmission, DVB also defines data connections (DVB-DATA - EN 301 192)

with return channels (DVB-RC) for several media (DECT, GSM, PSTN/ISDN, satellite etc.) and protocols (DVB-

IPTV: Internet Protocol; DVB-NPI: network protocol independent).

23

Older technologies such as teletext (DVB-TXT) and vertical blanking interval data (DVB-VBI) are also supported by

the standards to ease conversion. However, for many applications more advanced alternatives like DVB-SUB for

subtitling are available.

Encryption and metadata

The conditional access system (DVB-CA) defines a Common Scrambling Algorithm (DVB-CSA) and a physical

Common Interface (DVB-CI) for accessing scrambled content. DVB-CA providers develop their wholly proprietary

conditional access systems with reference to these specifications. Multiple simultaneous CA systems can be assigned

to a scrambled DVB program stream providing operational and commercial flexibility for the service provider.

DVB is also developing a Content Protection and Copy Management system for protecting content after it has been

received (DVB-CPCM), which is intended to allow flexible use of recorded content on a home network or beyond,

while preventing unconstrained sharing on the Internet. DVB-CPCM has been the source of much controversy in the

popular press and It is said that CPCM is the DVB's answer to the failed American Broadcast Flag.

DVB transports include metadata called Service Information (DVB-SI, ETSI EN 300 468, ETSI TR 101 211) that

links the various elementary streams into coherent programs and provides human-readable descriptions for electronic

program guides as well as for automatic searching and filtering.

Recently, DVB has adopted a profile of the metadata defined by the TV-Anytime Forum (DVB-TVA, ETSI TS

102323). This is an XML Schema based technology and the DVB profile is tailored for enhanced Personal Digital

Recorders. DVB lately also started an activity to develop a service for IPTV (DVB-IPI, ETSI TR 102033, ETSI TS

102034, ETSI TS 102814) which also includes metadata definitions for a broadband content guide (DVB-BCG, ETSI

TS 102 539).

Software platform

The DVB Multimedia Home Platform (DVB-MHP) defines a Java-based platform for the development of consumer

video system applications. In addition to providing abstractions for many DVB and MPEG-2 concepts, it provides

interfaces for other features like network card control, application download, and layered graphics.

Return channel

DVB has standardized a number of return channels that work together with DVB(-S/T/C) to create bi-directional

communication. RCS is short for Return Channel Satellite, and specifies return channels in C, Ku and Ka frequency

bands with return bandwidth of up to 2 Mbit/s. DVB-RCT is short for Return Channel Terrestrial, specified by ETSI

EN 301958.

Adoption

DVB-S and DVB-C were ratified in 1994. DVB-T was ratified in early 1997. The first commercial DVB-T broadcasts

were performed by the United Kingdom's Digital TV Group in late 1998. In 2003 Berlin, Germany was the first area

to completely stop broadcasting analog TV signals. Most European countries are fully covered by digital television

and many have switched off PAL/SECAM services.

In Europe, as well as in Australia, South Africa and India, DVB is used throughout. This also holds true for cable and

satellite in most Asian, African and many South American countries. Many of these have not yet selected a format for

digital terrestrial broadcasts (DTTV) and a few (Canada, El Salvador, Honduras, Mexico, South Korea and the United

States) have chosen ATSC instead of DVB-T.

UNIT II TELECOMMUNICATION SYSTEMS

Part A

1) What are the four types of handover available in GSM?

1. Intra cell Handover

2. Inter cell Intra BSC Handover

3. Inter BSC Intra MSC handover

4. Inter MSC Handover

2) What are the categories of Mobile services?

• Bearer services

• Tele services

• Supplementary services

3) What are the services provided by supplementary services?

• User identification

• Call redirection

• Call forwarding

• Closed user groups

• Multiparty Communication

4) What are types of Handover?

Intra-cell handover

Inter-cell, intra- BSC handover

Inter-BSC, intra-MSC handover

Inter MSC handover

5) What is meant by GPRS?

The General Packet Radio Service provides packet mode transfer for applications

that exhibit traffic patterns such as frequent transmission of small volumes.

6) What are subsystems in GSM system?

• Radio subsystem (RSS)

• Network & Switching subsystem (NSS)

• Operation subsystem (OSS)

7) What is 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) Define Normal Burst?

The frame used for normal data transmission within a time slot is called Normal Burst.

9) What are the logical channels in GSM?

• Traffic channel(TCH) • Control channel(CCH)

10) What is the function of Medium Access Control Layer?

The functions of Medium Access Control Layer is responsible for establishes,

maintains, and releases channels for higher layers by activating and deactivating physical

channels.

11) What is Handover?

The satellite is the base station in satellite communication systems and that itself is moving. So,

additional instance of handover are necessary due to the movement of the satellite

1. Intra Satellite handover:

2. Inter Satellite handover.

3. Gateway handover.

4. Inter System handover.

12) What is MSC?

Main Service Channel (MSC) carries all user data.

eg. audio, multimedia data.

13) 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.

14) What are the different types of disk?

• A flat disks

• Skewed disks

• Multi disks

15) What are the goals of DVB?

The goal of DVB is to introduce digital TV broadcasting using satellite transmission (DVB-5)

cable technology (DVB-c) and terrestrial transmission (DVB-7).

16) Name some of the formats supported by MOT?

• Multimedia and Hypermedia information coding experts group (MHEG)

• Join photograph’s experts group (JPEG)

• American standard code for information interchange (ASCII)

• Moving pictures expert group (MPEG)

• Hypertext markup language (HTML)

• Hypertext transfer protocol (HTTP)

• Bitmap (BMP)

• Graphics interchange format (GIF)

17) Give structure MOT object.

7bytes

variable size

variable size

Header core

Header Extension Body

Header core: contain the size of the header and body and the content type of the object.

Header Extension: contains additional object handling data such as repetition distance to support

caching, segmentation information and priority of the data.

Body: contains arbitrary data to be transmitted.

18) What are different interleaving and repetition schemes applied by DAB to objects and

segments?

1. Object Repetition.

2. Interleaved Objects.

3. Segment repetition.

4. Header repetition.

19) What are the advantages of DAB?

1. DAB can offer sound in CD like quality.

2. DAB can use single frequency network where all senders transmitting the same radio program

can operate at the same frequency.

3. DAB use VHF and UHF frequency bands.

4. DAB uses DQPSK modulation scheme.

5. DAB user COFDM and FEC.

6. DAB can transmit up to six stereo audio programmes with a data rate of 192kbit/s each.

20) What is object repetition?

DAB can repeat objects several times. If an object A consists of four segments (A1,A2,A3,A4) a

single repetition pattern would be A1A2A3A4A1A2A3A4A1A2A3A4……..

21) What is EIT?

Event Information Table (EIT) contains status information about the current transmission and

some additional information for set-top boxes.

22) What is the service information sent by DVB?

Digital Video Broadcast Containers are basically MPEG-2 frames. DVB sends service

information. This information is,

1. Network information table (NIT).

2. Service Description Table (SDT).

3. Event Information Table (EIT).

4. Time and Date Table (TDT)

23) What are the advantages of DVB?

1. Data rates planned for users are 6-38mbit/s for the downlink and 33-100kbit/s for the uplink.

2. Transmitted along with TV programmes and doesn’t require additional lines or hardware per

customer.

3. Can be used in remote areas and developing countries where there is no high bandwidth wired

network.

24) 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)

25) 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.

26) 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.

UNIT2 TELECOMMUNICATION SYSTEMS

Part B

1. Write notes on DECT and TETRA

System architecture, Protocol Architecture

2. Write notes on UMTS and IMT – 2000

UMTS basic architecture, UTRA FDD mode, UTRA TDD mode

3. Explain broadcast systems in detail.

Overview – Cyclical repetition of data – Digital audio broadcasting – Multimedia object transfer

protocol – Digital video broadcasting.

4. Explain satellite systems in detail.

History – Applications – Basics – GEO – LEO – MEO – Routing – Localization – Handover –

Examples.

5. Explain GSM systems in detail.

Mobile services- System Architecture – Radio interface – Protocols –

Localization and calling – Handover – Security - New data services –

6. Explain GPRS systems in detail.

System architecture, Protocol Architecture– Handover – Security.\

7. Explain DAB in detail.

Media access

Frequencies

second phase: one out of 9 frequency blocks in the L-band

Date-rates:

Modulation:

Digital services:

8. Explain DVB in detail.

Container

High-speed Internet

9. Explain the following a) Routing b) Hand over c) Localization

10. Explain the various satellite orbit and the parameters associated.

Parameters of satellites and explanations-Three orbits and explanation

1

UNIT III

WIRLESS LAN

Wireless LAN – IEEE 802.11 - Architecture – services – MAC – Physical layer – IEEE 802.11a -

802.11b standards – HIPERLAN – Blue Tooth.

WIRELESS LAN

Characteristics of wireless LANs

Advantages

o Very flexible within the reception area

o Ad-hoc networks without previous planning possible

o (almost) no wiring difficulties (e.g. historic buildings, firewalls)

o More robust against disasters like, e.g., earthquakes, fire - or users pulling a plug...

Disadvantages

o Typically very low bandwidth compared to wired networks (1-10 Mbit/s)

o Many proprietary solutions, especially for higher bit-rates, standards take their time

(e.g. IEEE 802.11)

o Products have to follow many national restrictions if working wireless, it takes a vary

long time to establish global solutions like, e.g., IMT-2000

Design goals for wireless LANs

o global, seamless operation

o low power for battery use

o no special permissions or licenses needed to use the LAN

o robust transmission technology

o simplified spontaneous cooperation at meetings

o easy to use for everyone, simple management

o protection of investment in wired networks

o security (no one should be able to read my data), privacy (no one should be able to collect user

profiles), safety (low radiation)

o transparency concerning applications and higher layer protocols, but also location awareness if

necessary

Comparison: infrared vs. radio transmission

2

Comparison: infrastructure vs. ad-hoc networks

IEEE 802.11 - ARCHITECTURE – SERVICES - ARCHITECTURE – SERVICES – MAC – PHYSICAL LAYER – IEEE 802.11A - 802.11B STANDARDS

802.11 - Architecture of an infrastructure network

Station (STA)

o terminal with access mechanisms to the wireless medium and radio contact to the

access point

Basic Service Set (BSS)

o group of stations using the same radio frequency

Access Point

o station integrated into the wireless LAN and the distribution system

Portal

o bridge to other (wired) networks

Distribution System

o interconnection network to form one logical network (EES: Extended Service Set)

based

on several BSS

3

802.11 - Architecture of an ad-hoc network

Direct communication within a limited range

o Station (STA):

terminal with access mechanisms to the wireless medium

o Basic Service Set (BSS):

group of stations using the same radio frequency

IEEE standard 802.11

802.11 - Layers and functions

MAC -Access mechanisms, fragmentation, encryption

MAC Management - Synchronization, roaming, MIB, power management

PLCP Physical Layer Convergence Protocol - Clear channel assessment signal (carrier sense)

PMD Physical Medium Dependent - Modulation, coding

PHY Management - Channel selection, MIB

Station Management - Coordination of all management functions

4

802.11 - Layers

802.11 - Physical layer

3 versions: 2 radio (typ. 2.4 GHz), 1 IR

o data rates 1 or 2 Mbit/s

FHSS (Frequency Hopping Spread Spectrum)

o spreading, despreading, signal strength, typ. 1 Mbit/s

o min. 2.5 frequency hops/s (USA), two-level GFSK modulation

DSSS (Direct Sequence Spread Spectrum)

o DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK

for 2 Mbit/s (Differential Quadrature PSK)

o preamble and header of a frame is always transmitted with 1 Mbit/s, rest of

transmission 1 or 2 Mbit/s

o chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)

o max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

Infrared

o 850-950 nm, diffuse light, typ. 10 m range

o carrier detection, energy detection, synchronization

802.11 - MAC layer I - DFWMAC

Traffic services

Asynchronous Data Service (mandatory)

exchange of data packets based on “best-effort”

support of broadcast and multicast

Time-Bounded Service (optional)

implemented using PCF (Point Coordination Function)

Access methods

DFWMAC-DCF CSMA/CA (mandatory)

collision avoidance via randomized „back-off“ mechanism

minimum distance between consecutive packets

ACK packet for acknowledgements (not for broadcasts)

DFWMAC-DCF w/ RTS/CTS (optional)

Distributed Foundation Wireless MAC

avoids hidden terminal problem

DFWMAC- PCF (optional)

access point polls terminals according to a list

5

Priorities

defined through different inter frame spaces

no guaranteed, hard priorities

SIFS (Short Inter Frame Spacing)

highest priority, for ACK, CTS, polling response

PIFS (PCF IFS)

medium priority, for time-bounded service using PCF

DIFS (DCF, Distributed Coordination Function IFS)

lowest priority, for asynchronous data service

802.11 - MAC layer

MAC address format

DS: Distribution System

AP: Access Point

DA: Destination Address

SA: Source Address

BSSID: Basic Service Set Identifier

RA: Receiver Address

TA: Transmitter Address

MAC management

Synchronization

try to find a LAN, try to stay within a LAN

timer etc.

Power management

sleep-mode without missing a message

periodic sleep, frame buffering, traffic measurements

Association/Reassociation

integration into a LAN

roaming, i.e. change networks by changing access points

scanning, i.e. active search for a network

MIB - Management Information Base

managing, read, write

scenario to DS from DS

address 1 address 2 address 3 address 4

ad-hoc network 0 0 DA SA BSSID -

infrastructure network, from AP

0 1 DA BSSID SA -

infrastructure network, to AP

1 0 BSSID SA DA -

infrastructure network, within DS

1 1 RA TA DA SA

6

HIPERLAN

• ETSI standard– European standard, cf. GSM, DECT, ...

– Enhancement of local Networks and interworking with fixed networks

– integration of time-sensitive services from the early beginning

• HIPERLAN family– one standard cannot satisfy all requirements

• range, bandwidth, QoS support

• commercial constraints

– HIPERLAN 1 standardized since 1996

physical layer

channel access

control layer

medium access

control layer

physical layer

data link layer

HIPERLAN layers OSI layers

network layer

7.31.1

higher layers

physical layer

medium access

control layer

logical link

control layer

IEEE 802.x layers

Original HIPERLAN protocol family

HIPERLAN 1 - Characteristics

Data transmission

point-to-point, point-to-multipoint, connectionless

23.5 Mbit/s, 1 W power, 2383 byte max. packet size

Services

asynchronous and time-bounded services with hierarchical priorities

compatible with ISO MAC

Topology

HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4

Application wireless LAN access to ATM fixed networks

wireless local loop

point-to-point wireless ATM connections

Frequency 5.1-5.3GHz 17.2-17.3GHz

Topology decentralized ad-hoc/infrastructure

cellular, centralized

point-to-multipoint

point-to-point

Antenna omni-directional directional

Range 50 m 50-100 m 5000 m 150 m

QoS statistical ATM traffic classes (VBR, CBR, ABR, UBR)

Mobility <10m/s stationary

Interface conventional LAN ATM networks

Data rate 23.5 Mbit/s >20 Mbit/s 155 Mbit/s

Power conservation

yes not necessary

7

infrastructure or ad-hoc networks

transmission range can be larger then coverage of a single node („forwarding“ integrated

in mobile terminals)

Further mechanisms

power saving, encryption, checksums

Services and protocols

CAC service

definition of communication services over a shared medium

specification of access priorities

abstraction of media characteristics

MAC protocol

MAC service, compatible with ISO MAC and ISO MAC bridges

uses HIPERLAN CAC

CAC protocol

provides a CAC service, uses the PHY layer, specifies hierarchical access mechanisms

for one or several channels

Physical protocol

send and receive mechanisms, synchronization, FEC, modulation, signal strength

HIPERLAN 1 - Physical layer

Scope

modulation, demodulation, bit and frame synchronization

forward error correction mechanisms

measurements of signal strength

channel sensing

Channels

3 mandatory and 2 optional channels (with their carrier frequencies)

mandatory

channel 0: 5.1764680 GHz

channel 1: 5.1999974 GHz

channel 2: 5.2235268 GHz

optional (not allowed in all countries)

channel 3: 5.2470562 GHz

channel 4: 5.2705856 GHz

BLUETOOTH

Consortium: Ericsson, Intel, IBM, Nokia, Toshiba - many members

Scenarios

connection of peripheral devices

loudspeaker, joystick, headset

support of ad-hoc networking

small devices, low-cost

bridging of networks

e.g., GSM via mobile phone - Bluetooth - laptop

Simple, cheap, replacement of IrDA, low range, lower data rates

2.4 GHz, FHSS, TDD, CDMA

8

Bluetooth MAC layer

Scatternets

UNIT III WIRELESS NETWORKS

Part A

1) 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.

2) What is meant by SIFS?

SIFS means Short Inter Frame Spacing. The shortest waiting time defined for short control

message such as acknowledgements or polling response.

3) What are Advantages of wireless LAN?

Flexibility, Planning, Design, Robustness, Quality Service, Cost, Proprietary Solution,

Restriction, Safety and Security

4) 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

5) What are the three Low Power States provided by Bluetooth?

PARK state

HOLD state

SNIFF state

6) What is SCO?

SCO-stands for Synchronous Connection Oriented Link

Standard telephone (voice) connection requires symmetrical, circuit-switched, point-to point

connections. For this type of link, the master reserves two consecutive slots at fixed intervals.

7) What are the three phases in EY-NPMA?

i. Prioritization: Determine the highest priority of a data packet ready to be sent on

competing nodes.

ii. Contention: Eliminate all but one of the contenders, if more than one sender has

the highest current priority.

iii. Transmission: Finally, transmit the packet of the remaining node.

8) What are Advantages and Disadvantages of Infrared?

Advantages:

i. Simple & extremely cheap senders and receivers which integrated in almost all mobile devices

ii. No licenses are needed for infrared technology and shielding is very simple.

iii. Electrical devices do not interfere with infrared transmission.

Disadvantages:

i. Low bandwidth

ii. Quite easily shielded

iii. Cannot Penetrate

9) What are the system integration functions of MAC management?

• Synchronization

• Power management

• Roaming

• Management information base (MIB)

10) What do you meant by roaming?

Moving between access point is called roaming. Even wireless networks may require more than

one access point to cover all rooms. In order to provide uninterrupted service, we require

roaming when the user moves from one access point to another.

11) What is mobile routing?

Even if the location of a terminal is known to the system, it still has to route the traffic through

the network to the access point currently responsible for the wireless terminal.

Each time a user moves to a new access point, the system must reroute traffic. This is known as

mobile routing.

12) What are the functions which support service and connection control?

>Access point control function

>Call control and connection control function

>Network security agent

>Service control function

>Mobility management function

13) What are the examples for service scenarios identified in WATM ?

>Office environments

>Universities, schools, training, centres

>Industry

>Hospitals

>Home

>Networked vehicles

14) What is BRAN?

The broadband radio access networks (BRAN) which have been standardized by

European Telecommunications Standard Institute( ETSI) are a possible choice for an RAL

for WATM. Although BRAN has been standardized independently from WATM, there is

co-operation between the two to concentrate the common efforts on one goal. The main

motivation behind BRAN is the deregulation and privatization of the telecommunication

sector in Europe.

15) What are the different network types of BRAN?

>Hyperlan1

>Hyperlan2

>Hyper access

>Hyperlink

16) What is the main problem for WATM during handover?

The main problem for WATM during the handover is rerouting of all connections and

maintaining connection quality.

17) What are the different segments in ATM end-to-end connection?

An ATM end-to-end connection is separated into different segments.

>A fixed segment is a part of the connection that is not affected by the handover

>Handover segment is affected by the handover and is located completely within a handover

domain.

18) What is anchor point?. The Anchor point is the boundary between a handover segment and a fixed

segment.

19) What are different types of handover?

>Hard handover

>Terminal initiated

>Network initiated

>Network initiated, terminal assisted

>Network controlled

>Backward handover

>Forward handover

20) What is mobile terminal and wireless terminal?.

Mobile terminal is a standard ATM terminal with the additional capability of reconnecting after

access point change. the terminal can be moved between different access point within a certain

domain. Wireless terminal is accessed via a wireless link, but the terminal itself is fixed,

i.e., the terminal keeps its access point to the network.

UNIT3 WIRELESS NETWORKS

Part B

1. Explain IEEE802.11 standard for WLANS in detail.

System architecture – Protocol architecture – Physical layer – Frequency hopping spread

spectrum, Direct spectrum spread spectrum, Infrared – Medium access control layer- Basic

DFWMAC-DCF using CSMA/CA, DFWMAC-DCF with RTS/CTS extension, DFWMAC-PCF

with polling, MC frames – MAC management –Synchronization, Power management, Roaming

– 802.11b.

2 Write notes on WATM services and Functions.

Wireless mobile terminal side functions and mobility supporting network side functions.

3. Write notes on WATM handover.

Handover reference model, handover requirements, types of handover, hand over scenarios,

backward handover, and forward handover.

4. Write notes on location management, addressing and access point control protocol.

Requirements for location management, procedures and entities

5. Give a detail note on HYPERLAN.

Reference model and configurations- Physical layer –Data link control layer – broadcast phase,

downlink phase, uplink phase, random access phasebroascast channel, frame channel, access

feedback channel, long transport channel, short transport channel, random channel –

Convergence layer – Ethernet, IEEE 1394 (Firewire), ATM.

6. Account on BLUETOOTH in detail.

User scenarios- Connection of peripheral devices, support of ad-hoc networking, bridging of

networks – Architecture – networking, protocol stackradio layer – Baseband layer- physical

links- synchronous connection-oriented link, Asynchronous connectionless link – link manager

protocol –L2CAP –Security –SDP – Profiles –IEEE802.15 .

1

UNIT IV

MOBILE NETWORK LAYER

Mobile IP – Dynamic Host Configuration Protocol - Routing – DSDV – DSR – Alternative Metrics

Mobile IP

A standard for mobile computing and networking

Computers doesn’t stay put.

Change location without restart its application or terminating any ongoing communication

IP Networking

Protocol layer

Network Layer

Transport Layer

What does IP do

moving packets from source to destination

No ’end-to-end’ guarantees

IP addresses

Network-prefix

Host portion

IP Routing

Packet Header

Network-prefix

Every node on the same link has the same network-prefix

Mobile IP Solves the following problems

f a node moves from one link to another without chnging its IP address, it will be unable to receive

packets at the new link; and

If a node moves from one link to another without chnging its IP address, it will be unable to receive

packets at the new link; and

Mobile IP Overview

Solution for Internet

Scalable, robust, secure, maintain communication

Use their permanent IP address

Routing protocol

Route packets to nodes that could potentially change location very rapidly

Layer 4-7, outside Mobile IP, but will be of major interest

2

Mobile IP: Terminology

• Mobile Node (MN)

– node that moves across networks without changing its IP address

• Correspondent Node (CN)

– ost with which MN is “corresponding” (TCP)

• Home Agent (HA)

– host in the home network of the MN, typically a router

– registers the location of the MN, tunnels IP packets to the COA

• Foreign Agent (FA)

– host in the current foreign network of the MN, typically a router

– forwards tunneled packets to the MN, typically the default router for MN

• Care-of Address (COA)

– address of the current tunnel end-point for the MN (at FA or MN)

– actual location of the MN from an IP point of view

Tunneling

An encapsulating IP packet including a path and an original IP packet

IP-in-IP encapsulation

IP-in-IP encapsulation

• IP-in-IP-encapsulation (mandatory in RFC 2003)

– tunnel between HA and COA

Care-of address COA

IP address of HA

TTL

IP identification

IP-in-IP IP checksum

flags fragment offset

lengthTOSver. IHL

IP address of MN

IP address of CN

TTL

IP identification

lay. 4 prot. IP checksum

flags fragment offset

lengthTOSver. IHL

TCP/UDP/ ... payload

3

Mobile IP and IPv6

Mobile IP was developed for IPv4, but IPv6 simplifies the protocols

Security is integrated and not an add-on, authentication of registration is included

COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address

auto configuration

No need for a separate FA, all routers perform router advertisement which can be used instead of the

special agent advertisement;

Addresses are always co-located

MN can signal a sender directly the COA, sending via HA not needed in this case (automatic

path optimization)

soft“hand-over, i.e. without packet loss, between two subnets is supported

MN sends the new COA to its old router

the old router encapsulates all incoming packets for the MN and forwards them to the new COA

Authentication is always granted

DHCP: Dynamic Host Configuration Protocol

Main idea: E.g WPI has pool of IP addresses it can “lease” to hosts for

short term use, claim back when done

Application

simplification of installation and maintenance of networked computers

Supplies systems with all necessary information, such as IP address, DNS server address, domain name,

subnet mask, default router etc.

enables automatic integration of systems into an Intranet or the Internet,

can be used to acquire a COA for Mobile IP

Client/Server-Model

the client sends via a MAC broadcast a request to the DHCP serve r (might be via a DHCP relay) client

relay server client

Dynamic Host Configuration Protocol (DHCP) is a network protocol for automatically assigning TCP/IP

information to client machines. Each DHCP client connects to the centrally-located DHCP server which

returns that client's network configuration, including the IP address, gateway, and DNS servers

DHCP is useful for automatic configuration of client network interfaces. When configuring the client

system, the administrator can choose DHCP and instead of entering an IP address, netmask, gateway, or

DNS servers. The client retrieves this information from the DHCP server. DHCP is also useful if an

administrator wants to change the IP addresses of a large number of systems. Instead of reconfiguring all

the systems, he can just edit one DHCP configuration file on the server for the new set of IP addresses. If

the DNS servers for an organization changes, the changes are made on the DHCP server, not on the DHCP

clients. Once the network is restarted on the clients (or the clients are rebooted), the changes take effect.

Furthermore, if a laptop or any type of mobile computer is configured for DHCP, it can be moved from

office to office without being reconfigured as long as each office has a DHCP server that allows it to

connect to the network.

4

Configuration File

The first step in configuring a DHCP server is to create the configuration file that stores the network

information for the clients. Global options can be declared for all clients, while other options can be

declared for individual client systems.

The configuration file can contain extra tabs or blank lines for easier formatting. Keywords are case-

insensitive and lines beginning with a hash mark (#) are considered comments.

Two DNS update schemes are currently implemented — the ad-hoc DNS update mode and the interim

DHCP-DNS interaction draft update mode. If and when these two are accepted as part of the Internet

Engineering Task Force (IETF) standards process, there will be a third mode — the standard DNS update

method. The DHCP server must be configured to use one of the two current schemes. Version 3.0b2pl11

and previous versions used the ad-hoc mode; however, it has been deprecated.

There are two types of statements in the configuration file:

Parameters — State how to perform a task, whether to perform a task, or what network

configuration options to send to the client.

Declarations — Describe the topology of the network, describe the clients, provide addresses for

the clients, or apply a group of parameters to a group of declarations.

Some parameters must start with the option keyword and are referred to as options. Options configure

DHCP options; whereas, parameters configure values that are not optional or control how the DHCP

server behaves.

In Example the routers, subnet-mask, domain-name, domain-name-servers, and time-offset options are used

for any host statements declared below it.

Additionally, a subnet can be declared, a subnet declaration must be included for every subnet in the

network. If it is not, the DHCP server fails to start.

In this example, there are global options for every DHCP client in the subnet and a range declared.

Clients are assigned an IP address within the range.

subnet 192.168.1.0 netmask 255.255.255.0 {

option routers 192.168.1.254;

option subnet-mask 255.255.255.0;

option domain-name "example.com";

option domain-name-servers 192.168.1.1;

option time-offset -18000; # Eastern Standard Time

range 192.168.1.10 192.168.1.100;

}

5

ROUTING

Motivation for Mobile IP

Routing

based on IP destination address, network prefix (e.g. 129.13.42)

determines physical subnet

change of physical subnet implies change of IP address to have a topological correct address

(standard IP) or needs special entries in the routing tables

Specific routes to end-systems?

change of all routing table entries to forward packets to the right destination

does not scale with the number of mobile hosts and frequent changes in the location, security

problems

Changing the IP-address?

adjust the host IP address depending on the current location

almost impossible to find a mobile system, DNS updates take to long time

Requirements to Mobile IP

Transparency

mobile end-systems keep their IP address

continuation of communication after interruption of link possible

point of connection to the fixed network can be changed

Compatibility

support of the same layer 2 protocols as IP

no changes to current end-systems and routers required

mobile end-systems can communicate with fixed systems

Security

authentication of all registration messages

Efficiency and scalability

only little additional messages to the mobile system required (connection typically via a low andwidth

radio link)

world-wide support of a large number of mobile systems in the whole

Internet

6

IPv6 availability

• Generally available with (new) versions of most operating systems.

• BSD, Linux 2.2 Solaris 8

• An option with Windows 2000/NT

• Most routers can support IPV6

• Supported in J2SDK/JRE 1.4

IPv6 Design Issues

• Overcome IPv4 scaling problem

• Lack of address space.

• Flexible transition mechanism.

• New routing capabilities.

• Quality of service.

• Security.

• Ability to add features in the future.

Mobile ad hoc networks

Standard Mobile IP needs an infrastructure

Home Agent/Foreign Agent in the fixed network DNS, routing etc. are not designed for mobility

Sometimes there is no infrastructure!

remote areas, ad-hoc meetings, disaster areas Cost can also be an argument against an infrastructure! no default router available every node should be able to forward

Traditional routing algorithms

Traditional algorithms are pro-active – i.e. operate independent of user-message demands. Suitable for

wired networks.

Distance Vector periodic exchange of messages with all physical neighbors that contain information about who

can be reached at what distance

selection of the shortest path if several paths available Link State

periodic notification of all routers about the current state of all physical links

routers get a complete picture of the network Example

ARPA packet radio network (1973), DV-Routing, up to 138 nodes every 7.5s exchange of routing tables including link quality updating of tables also by reception of packets routing problems solved with limited flooding

7

Problems of traditional routing algorithms

Dynamics of the topology

Frequent changes of connections, connection quality, participants Limited performance of mobile systems

periodic updates of routing tables need energy without contributing to the transmission of user data;

sleep modes difficult to realize

Limited bandwidth of the system is reduced even more due to the exchange of routing information

Links can be asymmetric, i.e., they can have a direction dependent transmission quality

Uncontrolled redundancy in links

Interference – ‘unplanned links’ (advantage?) DSDV (Destination Sequenced Distance Vector)

Early work

on demand version: AODV (Ad-hoc On-demand Distance Vector

Expansion of distance vector routing (but still pro-active) Sequence numbers for all routing updates

assures in-order execution of all updates avoids loops and inconsistencies

Decrease of update frequency (‘damping’)

store time between first and best announcement of a path inhibit update if it seems to be unstable (based on the stored time values)

Dynamic source routing Split routing into discovering a path and maintaining a path Discovering a path

Only if a path for sending packets to a certain destination is needed and no path is currently available (reactive algorithm) Maintaining a path

Only while the path is in use: make sure that it can be used continuously Path discovery

Broadcast a packet (Route Request) with destination address and unique ID

if a station receives a broadcast packet

if the station is the receiver (i.e., has the correct destination address) then return the packet to the sender

8

a ID) then Discard the packet

otherwise, append own address and broadcast packet

sender receives packet with the current path (address list) Maintaining paths

After sending a packet wait for a layer 2 acknowledgement (if applicable) listen into the medium to detect if other stations forward the packet (if possible) request an explicit acknowledgement

if a station encounters problems it can inform the sender of a packet or look-up a new path locally

ALTERNATIVE METRICS.

Mobile IP with reverse tunneling

Router accepts often only “topological correct“addresses (firewall!)

a packet from the MN encapsulated by the FA is now topological correct

furthermore multicast and TTL problems solved (TTL in the home network correct, but MN is to

far away from the receiver)

Reverse tunneling does not solve

problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms

(tunnel hijacking)

optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender

(double triangular routing)

The standard is backwards compatible

the extensions can be implemented easily and cooperate with current implementations without

these extensions

Agent Advertisements can carry requests for reverse tunneling

World Wide Web and mobility

Protocol (HTTP, Hypertext Transfer Protocol) and language

(HTML, Hypertext Markup Language) of the Web have not been designed for mobile applications and

mobile devices, thus creating many problems!

Typical transfer sizes

HTTP request: 100-350 byte

responses avg. <10 kbyte, header 160 byte, GIF 4.1kByte, JPEG

12.8 kbyte, HTML 5.6 kbyte

but also many large files that cannot be ignored

The Web is no file system

Web pages are not simple files to download

static and dynamic content, interaction with servers via forms, content transformation, push

technologies etc.

many hyperlinks, automatic loading and reloading, redirecting

a single click might have big consequences

UNIT 4 - NETWORK LAYER

1) What is generic routing encapsulation?

Generic routing encapsulation (GRE) is an encapsulation scheme which supports other network

protocols in addition to IP. It allows the encapsulation of packets of one protocol suite into the

payload portion of a packet of another protocol suite.

2) Define COA.

The COA (care of address) 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 the tunnel.

3) What is meant by Transparency?

Mobility should remain invisible for many higher layer Protocols and applications. The only

affects of mobility should be a higher delay and lower bandwidth which are natural in the case of

mobile networks.

4) What is Generic Routing encapsulation?

Generic Routing encapsulation (GRE) allows the encapsulation of packets of one protocol suite

into the payload portion of a packet of another protocol suit.

5) What is Binding Request?

Any node that wants to know the current location of an MN can send a binding request to the

HA. The HA can check if the MN has allowed dissemination of its current location.

6) What are the possibilities for the location of care-of-address (COA)?

The two possibilities for the location of care-of-address are:

i. Foreign agent COA

ii.Co-related COA

7) What are the requirements for the development of mobile IP standard?

The requirements are:

a.Compatibility

b.Transparency

c.Scalability and efficiency

d.Security

8) What is Dynamic source Routing?

Dynamic Source Routing eliminates all periodic routing updates. If a node needs to discover a

route, it broadcast a route request with a unique identifier and the destination address as

parameters. Any node that receivers a route request gives a list of addresses representing a

possible path on its way toward the destination.

9) Why is need of routing?

Routing is to find the path between source and destination and to forward the packets

appropriately.

10) Define Mobile node:

Mobile node:

A mobile node is an end-system or router that can change its point of attachment to the Internet

using mobile IP. The MN keeps its IP address and can continuously with any other system in the

Internet as long as link layer connectivity is given.

11) 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.

12) Define Dynamic source routing.

In an adhoc networks where nodes exchanges packets from time to time. Dynamic Source

routing divides the task of routing into two separate problems:

i) Routing Recovery: A node only tries to discover a route to destination if it has to send

something to this destination and there is currently no known route

ii) Route Maintenance: If a node is continuously sending packets via route, it has to make sure

that the route is held urgent. As soon as a node detects problem with the current route it has to

find an alternative node.

13) Define Compatibility.

support of the same layer 2 protocols as IP

no changes to current end-systems and routers required

mobile end-systems can communicate with fixed systems

14) What is Home Agent (HA)?

Home Agent (HA)

system in the home network of the MN, typically a router

registers the location of the MN, tunnels IP datagrams to the COA

15) Define Foreign Agent (FA).

system in the current foreign network of the MN, typically a router

forwards the tunneled datagrams to the MN, typically also the default router for the MN

16) Define Agent Advertisement.

HA and FA periodically send advertisement messages into their physical subnets

MN listens to these messages and detects, if it is in the home or a foreign network

MN reads a COA from the FA advertisement messages

17) Define Registration.

MN signals COA to the HA via the FA, HA acknowledges via FA to MN

these actions have to be secured by authentication

18) Define Key distribution

Home agent distributes session keys

foreign agent has a security association with the home agent

mobile host registers a new binding at the home agent

home agent answers with a new session key for foreign agent and mobile node

19) Applications of Dynamic Host Configuration Protocol.

simplification of installation and maintenance of networked computers

supplies systems with all necessary information, such as IP address, DNS server address,

domain name, subnet mask, default router etc.

enables automatic integration of systems into an Intranet or the Internet, can be used to

acquire a COA for Mobile IP

20) Define DSDV (Destination Sequenced Distance Vector).

Expansion of distance vector routing

Sequence numbers for all routing updates

assures in-order execution of all updates

avoids loops and inconsistencies

21) List the examples for interference based routing.

Least Interference Routing (LIR)

calculate the cost of a path based on the number of stations that can receive a transmission

Max-Min Residual Capacity Routing (MMRCR)

calculate the cost of a path based on a probability function of successful transmissions and

interference

Least Resistance Routing (LRR)

calculate the cost of a path based on interference, jamming and other transmissions

LIR is very simple to implement

UNIT4 NETWORK LAYER

Part B

1. Explain mobile IP in detail.

Goals, assumptions and requirements – Entities and terminology – IP packet delivery – Agent

discovery – Agent advertisement, Agent solicitation –Registration – Tunneling and

encapsulation- IP-in-IP encapsulation, minimal encapsulation, generic routing encapsulation –

optimizations – Reverse tunneling – IPv6.

2. Give a detailed account of mobile ad-hoc networks.

Instant infrastructure, Disaster relief Remote areas Effectiveness – Routing – Asymmetric links,

redundant links, interference, dynamic topology – Destination sequence distance vector –

sequence numbers, damping - Dynamic source routing – route discovery, route maintenance -

Alternative metrics – least interference routing.

3. Explain about DHCP: Dynamic Host Configuration Protocol.

Application

Client/Server-Model

DHCP - protocol mechanisms

DHCP characteristics

4. Discuss about Adhoc-networks.

Standard Mobile IP needs an infrastructure

Routing

Routing examples for an ad-hoc network

5. Explain about Traditional routing algorithms in detail.

Distance Vector- Link State

6. Explain about DSDV (Destination Sequenced Distance Vector) in detail.

Expansion of distance vector routing

Sequence numbers for all routing updates

Decrease of update frequency

7 .State Dynamic source routing in detail.

Discover a path

Maintaining a path Optimizations

8. Discuss about inference routing in detail.

Least Interference Routing (LIR)

Max-Min Residual Capacity Routing (MMRCR)

Least Resistance Routing (LRR)

1

UNIT V

TRANSPORT AND APPLICATION LAYERS

Traditional TCP – Classical TCP improvements – WAP, WAP 2.0.

TRADITIONAL TCP

TCP is an alternative transport layer protocol over IP.

• TCP provides:

• Connection-oriented

• Reliable

• Full-duplex

• Byte-Stream

Connection-Oriented

• Connection oriented means that a virtual connection is established before any user data is transferred.

• If the connection cannot be established - the user program is notified.

• If the connection is ever interrupted - the user program(s) is notified.

Reliable

• Reliable means that every transmission of data is acknowledged by the receiver.

• If the sender does not receive acknowledgement within a specified amount of time, the sender retransmits

the data

Byte Stream

• Stream means that the connection is treated as a stream of bytes.

• The user application does not need to package data in individual datagrams (as with UDP).

Buffering

• TCP is responsible for buffering data and determining when it is time to send a datagram.

• It is possible for an application to tell TCP to send the data it has buffered without waiting for a buffer to fill

up.

Full Duplex

• TCP provides transfer in both directions.

• To the application program these appear as 2 unrelated data streams, although TCP can piggyback control

and data communication by providing control information (such as an ACK) along with user data.

TCP Ports

• Interprocess communication via TCP is achieved with the use of ports (just like UDP).

• UDP ports have no relation to TCP ports (different name spaces).

TCP Segments

• The chunk of data that TCP asks IP to deliver is called a TCP segment.

• Each segment contains:

• data bytes from the byte stream

• control information that identifies the data bytes

2

TCP Lingo

• When a client requests a connection it sends a “SYN” segment (a special TCP segment) to the server port.

• SYN stands for synchronize. The SYN message includes the client’s ISN.

• ISN is Initial Sequence Number.

• Every TCP segment includes a Sequence Number that refers to the first byte of data included in the

segment.

• Every TCP segment includes an Acknowledgement Number that indicates the byte number of the next data

that is expected to be received.

• All bytes up through this number have already been received.

• There are a bunch of control flags:

• URG: urgent data included.

• ACK: this segment is (among other things) an acknowledgement.

• RST: error – connection must be reset.

• SYN: synchronize Sequence Numbers (setup)

• FIN: polite connection termination

• MSS: Maximum segment size (A TCP option)

• Window: Every ACK includes a Window field that tells the sender how many bytes it can send before the

receiver will have to toss it away (due to fixed buffer size).

CLASSICAL TCP IMPROVEMENTS

TCP Connection Creation

• Programming details later - for now we are concerned with the actual communication.

• A server accepts a connection.

• Must be looking for new connections!

• A client requests a connection.

• Must know where the server is!

Client Starts

• A client starts by sending a SYN segment with the following information:

• Client’s ISN (generated pseudo-randomly)

• Maximum Receive Window for client.

• Optionally (but usually) MSS (largest datagram accepted).

• No payload! (Only TCP headers)

Server Response

• When a waiting server sees a new connection request, the server sends back a SYN segment with:

• Server’s ISN (generated pseudo-randomly)

• Request Number is Client ISN+1

• Maximum Receive Window for server.

• Optionally (but usually) MSS

• No payload! (Only TCP headers)

• When the Server’s SYN is received, the client sends back an ACK with:

• Acknowledgment Number is Server’s ISN+1

3

TCP 3-way handshake

Client: “I want to talk, and I’m starting with byte number X”.

Server: “OK, I’m here and I’ll talk. My first byte will be called number Y, and I know your first byte will be

number X+1”.

Client: “Got it - you start at byte number Y+1”.

Bill: “Monica, I’m afraid I’ll syn and byte your ack”

TCP Data and ACK

• Once the connection is established, data can be sent.

• Each data segment includes a sequence number identifying the first byte in the segment.

• Each segment (data or empty) includes a request number indicating what data has been received

Buffering

• Keep in mind that TCP is part of the Operating System. The O.S. takes care of all these details

asynchronously.

• The TCP layer doesn’t know when the application will ask for any received data.

• TCP buffers incoming data so it’s ready when we ask for it.

TCP Buffers

• Both the client and server allocate buffers to hold incoming and outgoing data

• The TCP layer does this.

• Both the client and server announce with every ACK how much buffer space remains (the Window field in

a TCP segment).

Send Buffers

• The application gives the TCP layer some data to send.

• The data is put in a send buffer, where it stays until the data is ACK’d.

• The TCP layer won’t accept data from the application unless (or until) there is buffer space.

ACKs

• A receiver doesn’t have to ACK every segment (it can ACK many segments with a single ACK segment).

• Each ACK can also contain outgoing data (piggybacking).

• If a sender doesn’t get an ACK after some time limit, it resends the data.

TCP Segment Order

• Most TCP implementations will accept out-of-order segments (if there is room in the buffer).

• Once the missing segments arrive, a single ACK can be sent for the whole thing.

• Remember: IP delivers TCP segments, and IP is not reliable - IP datagrams can be lost or arrive out of

order.

Termination

• The TCP layer can send a RST segment that terminates a connection if something is wrong.

• Usually the application tells TCP to terminate the connection politely with a FIN segment.

4

TCP Sockets Programming

• Creating a passive mode (server) socket.

• Establishing an application-level connection.

• Sending/receiving data.

• Terminating a connection.

Establishing a passive mode TCP socket

Passive mode:

• Address already determined.

• Tell the kernel to accept incoming connection requests directed at the socket address.

• 3-way handshake

• Tell the kernel to queue incoming connections for us.

Accepting an incoming connection

• Once we start listening on a socket, the O.S. will queue incoming connections

• Handles the 3-way handshake

• Queues up multiple connections.

• When our application is ready to handle a new connection, we need to ask the O.S. for the next connection.

Terminating a TCP connection

• Either end of the connection can call the close() system call.

• If the other end has closed the connection, and there is no buffered data, reading from a TCP socket returns

0 to indicate EOF

Client Code

• TCP clients can connect to a server, which:

• takes care of establishing an endpoint address for the client socket.

• don’t need to call bind first, the O.S. will take care of assigning the local endpoint address

(TCP port number, IP address).

• Attempts to establish a connection to the specified server.

• 3-way handshake

Reading from a TCP socket

• By default read() will block until data is available.

• Reading from a TCP socket may return less than max bytes (whatever is available).

• You must be prepared to read data 1 byte at a time!

WIRELESS APPLICATION PROTOCOL (WAP)

Empowers mobile users with wireless devices to easily access and interact with information and services.

A “standard” created by wireless and Internet companies to enable Internet access from a cellular phone

WAP: Main Features

Browser

– “Micro browser”, similar to existing web browsers

Markup language

– Similar to HTML, adapted to mobile devices

5

Script language

– Similar to Javascript, adapted to mobile devices

Gateway

– Transition from wireless to wired world

Server

– “Wap/Origin server”, similar to existing web servers

Protocol layers

– Transport layer, security layer, session layer etc.

Telephony application interface

– Access to telephony functions

Internet Model

WAP Architecture

HTML

HTTP

TLS/SSL

TCP/IP

6

WAP Application Server

WAP: Network Elements

WAP Specifies

Wireless Application Environment

– WML Microbrowser

– WMLScript Virtual Machine

– WMLScript Standard Library

– Wireless Telephony Application Interface (WTAI)

– WAP content types

Wireless Protocol Stack

– Wireless Session Protocol (WSP)

– Wireless Transport Layer Security (WTLS)

– Wireless Transaction Protocol (WTP)

– Wireless Datagram Protocol (WDP)

– Wireless network interface definitions

7

WAP Stack

WAE (Wireless Application Environment):

– Architecture: application model, browser, gateway, server

– WML: XML-Syntax, based on card stacks, variables, ...

– WTA: telephone services, such as call control, phone book etc.

WSP (Wireless Session Protocol):

– Provides HTTP 1.1 functionality

– Supports session management, security, etc.

WTP (Wireless Transaction Protocol):

– Provides reliable message transfer mechanisms

– Based on ideas from TCP/RPC

WTLS (Wireless Transport Layer Security):

– Provides data integrity, privacy, authentication functions

– Based on ideas from TLS/SSL

WDP (Wireless Datagram Protocol):

– Provides transport layer functions

– Based on ideas from UDP

WHY WAP?

Wireless networks and phones

– have specific needs and requirements

– not addressed by existing Internet technologies

WAP

– Enables any data transport

• TCP/IP, UDP/IP, GUTS (IS-135/6), SMS, or USSD.

– Optimizes the content and air-link protocols

– Utilizes plain Web HTTP 1.1 servers

• leverages existing development methodologies

8

• utilizes standard Internet markup language technology (XML)

• all WML content is accessed via HTTP 1.1 requests

– WML UI components map well onto existing mobile phone user interfaces

• no re-education of the end-users

• leveraging market penetration of mobile devices

– Several modular entities together form a fully compliant Internet entity

WAP: “Killer” Applications

Location-based services

– Real-time traffic reporting, Event/restaurant recommendation

Enterprise solutions

– Email access, Database access, “global” intranet access

– Information updates “pushed” to WAP devices

Financial services

– Banking, Bill-paying, Stock trading, Funds transfers

Travel services

– Schedules and rescheduling, Reservations

Gaming and Entertainment

– Online, real-time, multi-player games

– Downloadable horoscopes, cartoons, quotes, advice

M-Commerce

– Shopping on the go

– Instant comparison shopping

– Location-based special offers and sales

Wireless Application Environment (WAE)

Goals

– device and network independent application environment

– for low-bandwidth, wireless devices

– considerations of slow links, limited memory, low computing power, small display, simple user

interface (compared to desktops)

– integrated Internet/WWW programming model

– high interoperability

WAE Components

Architecture

– Application model, Microbrowser, Gateway, Server

User Agents

– WML/WTA/Others

– content formats: vCard, vCalendar, Wireless Bitmap, WML, ...

WML

– XML-Syntax, based on card stacks, variables, ...

WMLScript

– procedural, loops, conditions, ... (similar to JavaScript)

WTA

– telephone services, such as call control, text messages, phone book, ... (accessible from

WML/WMLScript)

Proxy (Method/Push)

9

WAE: Logical Model

WML: Wireless Markup Language

Tag-based browsing language:

– Screen management (text, images)

– Data input (text, selection lists, etc.)

– Hyperlinks & navigation support

Takes into account limited display, navigation capabilities of devices

XML-based language

– describes only intent of interaction in an abstract manner

– presentation depends upon device capabilities

Cards and Decks

– document consists of many cards

– User interactions are split into cards

– Explicit navigation between cards

– cards are grouped to decks

– deck is similar to HTML page, unit of content transmission

Events, variables and state mgmt

The basic unit is a card. Cards are grouped together into Decks Document ~ Deck (unit of transfer)

All decks must contain

– Document prologue

XML & document type declaration

– <WML> element

Must contain one or more cards

WML Example

WML>

<CARD>

<DO TYPE=“ACCEPT”>

<GO URL=“#eCard”/>

</DO

Welcome!

</CARD>

<CARD NAME=“eCard”>

<DO TYPE=“ACCEPT”>

<GO URL=“/submit?N=$(N)&S=$(S)”/>

</DO>

Enter name: <INPUT KEY=“N”/>

Choose speed:

10

<SELECT KEY=“S”>

<OPTION VALUE=“0”>Fast</OPTION>

<OPTION VALUE=“1”>Slow</OPTION>

<SELECT>

</CARD>

</WML>

WMLScript

Complement to WML

– Derived from JavaScript™

Provides general scripting capabilities

– Procedural logic, loops, conditionals, etc.

– Optimized for small-memory, small-cpu devices

Features

– local user interaction, validity check of user input

– access to device facilities (phone call, address book etc.)

– extensions to the device software

• configure device, download new functionality after deployment

Bytecode-based virtual machine

– Stack-oriented design, ROM-able

– Designed for simple, low-impact implementation

WMLScript compiler resides in the network

WMLScript Libraries

Lang - VM constants, general-purpose math functionality, etc.

String - string processing functions

URL - URL processing

Browser - WML browser interface

Dialog - simple user interface

Float - floating point functions

Wireless Telephony Application (WTA)

Collection of telephony specific extensions

– designed primarily for network operators

Example

– calling a number (WML)

wtai://wp/mc;07216086415

– calling a number (WMLScript)

WTAPublic.makeCall("07216086415");

Implementation

– Extension of basic WAE application model

– Extensions added to standard WML/WMLScript browser

– Exposes additional API (WTAI)

WTA Features

Extension of basic WAE application model

– network model for interaction

11

• client requests to server

• event signaling: server can push content to the client

– event handling

• table indicating how to react on certain events from the network

• client may now be able to handle unknown events

– telephony functions

• some application on the client may access telephony functions

WTAI includes:

– Call control

– Network text messaging

– Phone book interface

– Event processing

Security model: segregation

– Separate WTA browser

– Separate WTA port

WAP Push Services

Web push

– Scheduled pull by client (browser)

• example: Active Channels

– no real-time alerting/response

• example: stock quotes

Wireless push

– accomplished by using the network itself

• example: SMS

– limited to simple text, cannot be used as starting point for service

• example: if SMS contains news, user cannot request specific news item

WAP push

– Network supported push of WML content

• example: Alerts or service indications

– Pre-caching of data (channels/resources)

Push Access Protocol

Based on request/response model

Push initiator is the client

Push proxy is the server

Initiator uses HTTP POST to send push message to proxy

Initiator sends control information as an XML document, and content for mobile (as WML)

Proxy sends XML entity in response indicating submission status

Initiator can

– cancel previous push

– query status of push

– query status/capabilities of device

Push Proxy Gateway

WAP stack (communication with mobile device)

TCP/IP stack (communication with Internet push initiator)

Proxy layer does

– control information parsing

– content transformation

– session management

12

– client capabilities

– store and forward

– prioritization

– address resolution

– management function

WTP Services and Protocols

WTP (Transaction)

– provides reliable data transfer based on request/reply paradigm

• no explicit connection setup or tear down

• optimized setup (data carried in first packet of protocol exchange)

• seeks to reduce 3-way handshake on initial request

– supports

• header compression

• segmentation /re-assembly

• retransmission of lost packets

• selective-retransmission

• port number addressing (UDP ports numbers)

• flow control

– message oriented (not stream)

– supports an Abort function for outstanding requests

– supports concatenation of PDUs

– supports User acknowledgement or Stack acknowledgement option

• acks may be forced from the WTP user (upper layer)

• default is stack ack

WAP 2.0.

WSP - Wireless Session Protocol

Goals

– HTTP 1.1 functionality

• Request/reply, content type negotiation, ...

– support of client/server transactions, push technology

– key management, authentication, Internet security services

WSP Services

– provides shared state between client and server, optimizes content transfer

– session management (establish, release, suspend, resume)

– efficient capability negotiation

– content encoding

– push

WSP/B (Browsing)

– HTTP/1.1 functionality - but binary encoded

– exchange of session headers

– push and pull data transfer

– asynchronous requests

WSP Overview

Header Encoding

– compact binary encoding of headers, content type identifiers and other well-known textual or

structured values

– reduces the data actually sent over the network

Capabilities (are defined for):

13

– message size, client and server

– protocol options: Confirmed Push Facility, Push Facility, Session Suspend Facility,

Acknowledgement headers

– maximum outstanding requests

– extended methods

– header code pages

Suspend and Resume

– server knows when client can accept a push

– multi-bearer devices

– dynamic addressing

– allows the release of underlying bearer resources

Session Context and Push

– push can take advantage of session headers

– server knows when client can accept a push

Connection-mode

– long-lived communication, benefits of the session state, reliability

Connectionless-mode

– stateless applications, no session creation overhead, no reliability overhead

WAP: Ongoing Work

WDP

– Tunnel to support WAP where no (end-to-end) IP bearer available

WTLS

– support for end-to-end security (extending WTLS endpoint beyond WAP Gateway)

– interoperable between WAP and Internet (public key infrastructure)

– integrating Smart Cards for security functions

WTP

– efficient transport over wireless links (wireless TCP)

– bearer selection/switching

– quality of service definitions

WSP

– quality of service parameters

– multicast data, multimedia support

WAE

– User agent profiles: personalize for device characteristics, preferences etc

– Push architecture, asynchronous applications

– Billing

UNIT 5 - TRANSPORT AND APPLICATION LAYERS

Part A

1) What are the two functions of the transport layer in the internet?

The two functions of the transport layer in the internet are check summing over user data and

multiplexing/ demultiplexing of data from applications.

2) What is called the exponential growth of the congestion window?

The senders always calculate congestion window for a window start size of the congestion

window is one segment. Sender sends one packet and waits for acknowledgement. If

acknowledgement arises it raises the level of congestion window by one. If sender sends two

packets if acknowledgement arises it raises the level of congestion window by two. This scheme

raises the level of congestion window every time the acknowledges come back, which takes

round trip time (RTT).This is called the exponential growth of the congestion window

3) Advantages of I-TCP:

•I-TCP does not require any changes in the TCP protocol as used by the hosts in the fixed

network or other hosts in a wireless network that do not use this optimization.

•Without partitioning retransmission of lost packets would take place between mobile host and

correspondent host across the whole network.

•Optimization of new mechanisms is quite simple to be done in I-TCP as they only cover a single

hop.

•The short delay between the mobile host and foreign agent can be determined and is

independent of other traffic streams. Therefore an optimized TCP can use precise time-outs to

guarantee retransmission as fast as possible.

•Partitioning into two connections also allows the use of a different transport layer protocol

between the foreign agent and the mobile host or the use of compressed headers etc. The foreign

agent can act as a gateway to translate between different protocols.

4) Disadvantages of I-TCP:

• The loss of the end to end semantics of TCP cause problems if the foreign agent portioning the

TCP connection crashes.

• An increased handover latency is more problematic in practical use

• The foreign agent must be a trusted entity because the TCP connections end at this point.

5) Define Slow Start?

TCP’s reaction to a missing acknowledgement is quite drastic, but necessary to get rid of

congestion. The behaviour TCP shows after the detection of congestion is called Slow start.

6) How does data transmission takes place?

Data transmission takes place using network adapters, fibre optics, copper wires, special

hardware for routers etc.

7) What is mean by SCPS-TP?

The set of protocols developed for space communication is known as space communications

protocol standards (SCPS), the extended TCP is called SCPS-transport protocols.(SCPS-TP).

8) What are Advantage and Disadvantage of MobileTCP?

Advantage:

i. M-TCP maintains the TCP end-to-end semantice. The SH does not send any ACK itself but

forwards the ACKs from the MH.

ii.If the MH is disconnected, M_TCP avoids useless retransmissions, slow starts or breaking

connections by simply shrinking the sender’s window to 0;

iii. Since M-TCP does not buffer data in the SH as I-TCP does, it is not necessary to forward

buffers to a new SH. Lost packets will be automatically retransmitted to the new SH.

Disadvantage:

i. As the SH does not act as proxy as in I-TCP, packet loss on the wireless link due to bit errors is

propagated to the sender. M-TCP assumes low bit error rates, which is not always a valid

assumption.

ii. A modified TCP on the wireless link not only requires modification to the MH protocol

software but also new network elements like the bandwidth manager.

9) What is fast retransmit?

In TCP, a receiver sends acknowledgements only if it receive any packets from the sender. Thus

receiving acknowledgements from a receiver shows additionally that the receiver continuously

receives something from the sender. Therefore, the gap in the packet stream is not due to severe

congestion, but a simple packet loss due to a transmission error. The sender can now retransmit

the missing packets before the timer expires. This behaviour is called fast retransmit.

10) What is fast recovery?

The receipt of acknowledgement shows that there is no congestion justifying a slow start. The

sender can continue with the current congestion window. The sender performs a fast recovery

from the packet loss. This mechanism can improve the efficiency of TCP dramatically.

11) 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.

12) 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.

13) 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.

14) 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.

15) Define Damping

Transient changes in topology that are short duration should not destabilize the routing

mechanism. Advertisements containing changes in topology currently stored are therefore not

disseminated further. A node waits with dissemination if these changes are most likely not yet

stable.Waitingg time depends on the time between the first and the best announcement.

1

UNIT5 TRANSPORT AND APPLICATION LAYERS

Part B

1. Write notes on traditional TCP.

Congestion controls, slow start, fast retransmit/ fast recovery, implications on mobility.

2. Write notes on wireless TCP.

Indirect TCP, snooping TCP, Mobile TCP, Fast retransmit/fast recovery,

transmission/time-out freezing, selective retransmission, transaction oriented TCP.

3. Write notes on WDP and WTLS.

Figure and explanation about WDP and WTLS.

4. Write notes on wireless transaction protocol.

Figure and explanation about WTP class 0, class 1 and class 2.

5. Write notes on wireless sessions protocol.

WSP/B over WTP and WSP/ B as connectionless session service

6. Explain Traditional TCP

Architecture-Types- Frame formats-Explanation

7. Explain in detail about WAP.

Architecture-Types-Forum-Advantages-Disadvantages

8. Discuss about WMLBrowser.

Browser library-functions-Security.

MOBILE COMPUTING

UNIT 1 WIRELESS COMMUNICATION FUNDAMENTALS

TWO MARK QUESTIONS IN UNIT-1

1. Define CDMA.

2. Define Signal.

3. What is digital modulation?

4. Define code division multiplexing.

5. List out the advantages of frequency division multiplexing.

6. What are the several versions in CSMA?

7. What is Quadrature Amplitude Modulation?

8. What are the 2 sub layers in DLC?

9. Define time division multiplexing.

10. List out the different types of frequencies used for data transmission.

11. Define Antenna.

12. List out the different types of antennas.

13. Define Modulation.

14. What is hidden and exposed terminal problem?

15. Define polling.

16. What is spread spectrum?

17. List out the different types of spread spectrum techniques.

18. Distinguish between ALOHA and slotted ALOHA.

19. Define fading.

20. Distinguish between DSSS and FHSS.

21. What are the 3 fundamental propagation behaviors depending on their frequency?

22. What is multipath propagation?

23. What is guard space?

24. What are the 3 different basic schemes analog modulations?

25. What is the use of Phase Lock Loop (PLL)?

26. What is hopping sequence?

27. What is dwell time?

28. What are the advantages of cellular systems?

29. What is browsing channel allocation and fixed channel allocation?

30. What are the disadvantages of cellular systems?

31. What is digital sense multiple access?

32. What is Network and Switching subsystem?

33. What is authentication centre?

34. What is called burst and normal burst?

35. What are the basic groups of logical channels?

36. Define traffic multiframe and control multiframe?

BIG QUESTIONS IN UNIT-1

1. Explain different TDMA schemes in detail.

2. Explain multiplexing in detail.

3. Discuss Modulation techniques in detail.

4. Account on CDMA Scheme.

5. Explain FDMA in detail.

6. Discuss SDMA in detail.

7. Explain major types of networks.

8. Explain types of Antennas in detail.

9. Explain the various applications of mobile computing.

10. Explain about the signal propagation.

11. Discuss about the cellular system.

12. List the difference between S/T/F/CDMA.

13. What is spread spectrum with its types.

14. Why do MAC scheme in wired network fail in wireless networks and how dose the

multiple access with collision avoidance (MACA) scheme work.

15. Define modulation and explain the method for analog modulation techniques in

details.

16. Discuss briefly the advanced phase shift keying.

UNIT II TELECOMMUNICATION SYSTEMS

TWO MARK QUESTIONS IN UNIT-II

1. What is Handover?

2. What are the categories of Mobile services?

3. What is TETRA?

4. What is meant by GPRS?

5. What are subsystems in GSM system?

6. What is meant by GEO?

7. Define the inclination angle and perigee.

8. Define the elevation angle and footprint.

9. What is MSC?

10. What are the different types of disk?

11. What are the goals of DVB?

12. Name some of the formats supported by MOT?

13. What are the advantages of DAB?

14. What is object repetition?

15. What is EIT?

16. What are the service information sent by DVB?

17. What is Active scanning?

18. What is Passive Scanning?

19. What is FIC?

20. What are the registers maintained by the gateway of satellite?

21. Specify the security services offered by GSM.

22. What is the frequency range of uplink and downlink in GSM network?

23. What are the two basic groups of logical channels in GSM?

24. What are the control channel groups in GSM?

25. List out the numbers needed to locate an MS and to address the MS.

26. What are the four possible handover scenarios in GSM?

27. What are the security services offered by GSM?

28. What is meant by GGSN?

29. What is meant by SGSN?

30. What is meant by BSSGP?

31. Define the protocol architecture of DECT.

32. Specify the standards offered by TETRA.

33. How many ITU standardized groups of 3G radio access technologies are there in

IMT-2000?

34. What are the steps perform during the search for a cell after power on?

35. What are the two basic classes of handover?

36. What are the two basic transport mechanisms used by DAB?

37. What are the two transport modes defined for MSC?

38. Define the terms: i. Earth Station. ii. Uplink.

39. Define Elevation Angle.

40. What are the factors limited the number of sub channels provided within the

satellite channel?

BIG QUESTIONS IN UNIT-II

1. Write notes on DECT and TETRA.

2. Write notes on UMTS and IMT – 2000.

3. Explain broadcast systems in detail.

4. Explain satellite systems in detail.

5. Explain GSM systems in detail.

6. Explain GPRS systems in detail.

7. Explain DAB in detail.

8. Explain DVB in detail.

9. Explain the following a) Routing b) Hand over c) Localization.

10. Explain the various satellite orbit and the parameters associated.

11. Compare GEO, MEO and LEO

UNIT III WIRELESS NETWORKS

TWO MARK QUESTIONS IN UNIT-3

1. What is the primary goal of IEE 802.11?

2. What is meant by SIFS?

3. What are Advantages of wireless LAN?

4. What are Design Goals of Wireless LAN?

5. What are the three Low Power States provided by Bluetooth?

6. What is SCO?

7. What are Advantages and Disadvantages of Infrared?

8. What are the system integration functions of MAC management?

9. What do you meant by roaming?.

10. What is mobile routing?

11. What are the functions which support service and connection control?

12. What are the examples for service scenarios identified in WATM ?

13. What is BRAN?

14. What are the different network types of BRAN?

15. What is the main problem for WATM during handover?

16. What are the different segments in ATM end-to-end connection?

17. What is anchor point? .

18. What are different types of handover?

19. What is mobile terminal and wireless terminal?.

20. Mention some of the disadvantages of WLANS?

21. Mention the design goals of WLANS?

22. What is the difference between infrastructure and ad-hoc networks?

23. Mention the features of infrared transmission?

24. What are the disadvantages of infrared transmission?

25. Mention the features of radio transmission?

26. What are the disadvantages of radio transmission?

27. Define frequency hopping spread spectrum?

28. Define random back off time?

29. What is Traffic Indication Map?

30. What is Delivery Traffic Indication Map?

31. What is Ad-hoc TIM?

32. Mention the features of HIPERLAN1?

33. What are the three phases of medium access in EY-NPMA?

34. Mention the elements of Bluetooth core protocols?

35. What is the purpose of sniff state?

36. What is the use of hold state?

37. What is the purpose of park state?

BIG QUESTIONS IN UNIT-3

1. Explain the architecture and features of IEEE 802.11 in details

2. Write notes on WATM services and Functions.

3. Write notes on WATM handover.

4. Write notes on location management, addressing and access point control

protocol.

5. Give a detail note on HYPERLAN

6. Account on BLUETOOTH in detail.

7. Discuss in detail about the different services of IEEE802.11.

8. Explain in detail about Adhoc networks.

9. List out the Advantages and Disadvantages of Infrastructure network and adhoc

network.

10. Explain the MAC layer in IEEE802.11

11. Explain how power management is done in IEEE 802.11 infrastructure based and

ad hoc networks.

12. Discuss how to increase the quality of service in an ad hoc network.

UNIT IV NETWORK LAYER

TWO MARK QUESTIONS IN UNIT-IV

1. What is generic routing encapsulation?

2. Define COA.

3. What is meant by Transparency?

4. What is Binding Request?

5. What are the possibilities for the location of care-of-address (COA)?

6. What are the requirements for the development of mobile IP standard?

7. Why is need of routing?

8. What is Dynamic source Routing?

9. Define Mobile node.

10. What is Encapsulation and Decapsulation?

11. Define Compatibility.

12. What is Home Agent (HA)?

13. Define Foreign Agent (FA).

14. Define Agent Advertisement.

15. Define Registration.

16. Define Key distribution.

17. Applications of Dynamic Host Configuration Protocol.

18. Define DSDV (Destination Sequenced Distance Vector).

19. List the examples for interference based routing.

20. Define tunneling.

21. What are the requirements of mobile IP?

22. Mention the different entities in a mobile IP.

23. What do you mean by mobility binding?

24. Define a tunnel.

25. Define an outer header

26. Define an inner header.

27. What is the use of network address translation?

28. Define triangular routing.

29. What is meant by a binding cache?

30. Define binding request.

31. What is known as Binding update?

32. Explain binding acknowledgement.

33. Define binding warning.

34. Explain cellular IP.

35. What are the advantages of cellular IP?

36. What is known as mobility anchor point?

37. Explain destination sequence distance vector routing.

38. What are the two things added to the distance vector algorithm?

39. How the dynamic source routing does divide the task of routing into two separate

problems?

BIG QUESTIONS IN UNIT-IV

1. Explain mobile IP in detail.

2. Give a detailed account of mobile ad-hoc networks.

3. Explain about DHCP: Dynamic Host Configuration Protocol.

4. Discuss about Adhoc-networks.

5. Explain about Traditional routing algorithms in detail.

6. Explain about DSDV (Destination Sequenced Distance Vector) in detail.

7. State Dynamic source routing in detail.

8. Discuss about inference routing in detail.

9. Explain the following :a)Agent Advertisement b)Encapsulation

10. Explain the following:a)Registration b)Tunneling.

11. a. What are the requirements of a mobile IP? (8) b. Describe Dynamic host

configuration protocol. (8)

12. a. Discuss the routing algorithm in ad-hoc network (8) b. What are the entities in

mobile IP? (8)

13. a. Discuss how optimization in achieved in mobile IP (8).b. Explain tunneling and

encapsulation in mobile IP. (8)

14. Explain how dynamic source routing protocols handles routing with an example

UNIT V TRANSPORT AND APPLICATION LAYERS

TWO MARK QUESTIONS IN UNIT-V

1. What are the two functions of the transport layer in the internet?

2. What is called the exponential growth of the congestion window?

3. List out the advantages of I-TCP.

4. List out disadvantages of I-TCP.

5. Define Slow Start.

6. How does data transmission takes place?

7. What is mean by Slow Start?

8. What is mean by SCPS-TP?

9. What are Advantages and Disadvantages of MobileTCP?

10. What is Fast retransmit?

11. What is fast recovery?

12. What is HTTP?

13. What is WAP?

14. What is WML Browser?

15. List out advantages of Transmission Freezing.

16. Define WAE.

17. What is WML?

18. Write short notes on WAP forum.

19. Distinguish between Traditional TCP and wireless TCP?

20. What is WTP? What are its classes?

21. List out the network elements of WAP.

22. What is the purpose of congestion window in classical TCP?

23. What is slow start?

24. What is the use of congestion threshold?

25. What led to the development of Indirect TCP?

26. What is the goal of M-TCP?

27. What do you mean by persistent mode?

28. What are the characteristics of 2.5G/3.5G wireless networks?

29. What are the configuration parameters to adapt TCP to wireless environments?

30. State the requirements of WAP.

31. Name the layers of WAP.

32. Name some ICMP messages.

33. What is WTP? What are its classes?

34. What is WSP?

35. Name some features of WSP adapted to web browsing.

36. What is WML?

37. What are the features of WML?

38. What are the advantages of WML Script over WML?

39. Name the libraries specified by WML Script.

40. What are the classes of libraries?

41. Name the operations performed by PAP.

42. What are the components of WAP2.0?

BIG QUESTIONS IN UNIT-V

1. Explain in detail about traditional TCP.

2. Explain about Classical TCP improvement techniques in detail.

3. Write notes on WDP and WTLS.

4. Write notes on wireless sessions protocol

5. Explain in detail about WAP.

6. Discuss about WAE and WTP.

7. Explain the following: Snooping TCP and Indirect TCP.

8. Explain the following: Selective repeat and Fast retransmit and recovery.

9. Explain the following: Freezing and transaction oriented TCP.

10. Explain about WML and WML script with the help of an example.

11. Explain classical TCP improvements and snooping TCP.

12. Explain the concept of wireless markup language.

13. Explain wireless application protocols with the it’s version WAP 2.0in detail.

Describe the operation of the window flow control mechanism

UNIT-1 WIRELESS COMMUNICATION FUNDAMENTALS

Part-1 (2 Marks)

1. What are the 3 fundamental propagation behaviors depending on their frequency?

2. What is multipath propagation?

3. What is guard space?

4. What is the 3 different basic shemes analog modulation?

5. What is the use of Phase Lock Loop (PLL)?

6. What is hopping sequence?

7. What is dwell time?

8. What are the advantages of cellular systems?

9. What is browsing channel allocation and fixed channel allocation?

10. What are the disadvantages of cellular systems?

11. What is digital sense multiple access?

12. What is Network and Switching subsystem?

13. What is authentication centre?

14. What is called burst and normal burst?

15. What are the basic groups of logical channels?

16. Define traffic multi frame and control multi frame?

17. What is OVSF?

18. Specify the steps perform during the search for a cell after power on?

19. Explain about transparent mode?

20. What are the basic classes of handovers?

Part -B

1. Explain about Mobile services (16)

2. Explain System architecture (16)

3. Explain briefly about TETRA (16)

4. Write brief about UMTS and IMT-2000(16)

5. Explain about UTRAN (16)

UNIT-2- TELECOMMUNICATION NETWORKS

Part -1(2 Marks)

1. Specify the security services offered by GSM.

2. What is the frequency range of uplink and downlink in GSM network?

3. What are the two basic groups of logical channels in GSM?

4. What are the control channel groups in GSM?

5. List out the numbers needed to locate an MS and to address the MS.

6. What are the four possible handover scenarios in GSM?

7. What are the security services offered by GSM?

8. What is meant by GGSN?

9. What is meant by SGSN?

10. What is meant by BSSGP?

11. Define the protocol architecture of DECT.

12. Specify the standards offered by TETRA.

13. How many ITU standardized groups of 3G radio access technologies are there in IMT-2000?

14. What are the steps perform during the search for a cell after power on?

15. What are the two basic classes of handover?

16. What are the two basic transport mechanisms used by DAB?

17. What are the two transport modes defined for MSC?

18. Define Elevation Angle.

19. What are the factors limited the number of sub channels provided within the satellite channel?

Part-B

1. Explain GSM architecture (16)

2. Explain Satellite networks in detail (16)

3. Write short notes on DAB (16)

4. Write short notes on DVB (16)

5. Explain about DECT (16)

UNIT-III WIRLESS LAN IT 1402 – MOBILE COMPUTING

Part-A (2 marks)

1. What are the advantages of WLANS?

2. Mention some of the disadvantages of WLANS?

3. Mention the design goals of WLANS?

4. What is the difference between infrastructure and ad-hoc networks?

6. Mention the features of infrared transmission?

7. What are the disadvantages of infrared transmission?

8. Mention the features of radio transmission?

10. Define frequency hopping spread spectrum?

11. Define random back off time?

12. What is Traffic Indication Map?

13. What is Delivery Traffic Indication Map?

14. What is Ad-hoc TIM?

15. What is meant by roaming?

16. Mention the features of HIPERLAN1?

17. What are the three phases of medium access in EY-NPMA?

18. Mention the elements of Bluetooth core protocols?

19. What is the purpose of sniff state?

20. What is the use of hold state?

21. What is the purpose of park state?

Part-B

1. Explain the architecture of IEEE 802.11(16)

2. Explain the MAC layer in IEEE802.11 (16)

3. Explain HIPERLAN 1 in detail HIPERLAN 1(16)

4. Explain about WATM (16)

5. Writ e short notes on Bluetooth. (16)

UNIT: 4- MOBILE NETWORK LAYER

Part –A (2 marks)

1. What are the requirements of mobile IP?

2. Mention the different entities in a mobile IP.

3. What do you mean by mobility binding?

4. Define a tunnel.

5. What is encapsulation?

6. What is decapsulation?

7. Define an outer header.

8. Define an inner header.

9. What is meant by generic routing encapsulation?

10. What is the use of network address translation?

11. Define triangular routing.

12. What is meant by a binding cache?

13. Define binding request.

14. What is known as Binding update?

15. Explain binding acknowledgement.

16. Define binding warning.

17. Explain cellular IP.

18. What are the advantages of cellular IP?

19. What is known as mobility anchor point?

20. Explain destination sequence distance vector routing

21. What are the two things added to the distance vector algorithm?

22. How the dynamic source routing does divide the task of routing into two separate problems?

Part -B

1. What are the requirements of a mobile IP? (16)

2. What are the entities in mobile IP? (16)

3. Explain tunneling and encapsulation in mobile IP. (16)

4. Describe Dynamic host configuration protocol. (16)

5. Explain routing in IPv6. (16)

UNIT-V TRANSPORT AND APPLICATION LAYERS

Part-A (2 marks)

1. What is slow start?

2. What is the use of congestion threshold?

3. What led to the development of Indirect TCP?

4. What is the goal of M-TCP?

5. What do you mean by persistent mode?

6. What are the characteristics of 2.5G/3.5G wireless networks?

7. What are the configuration parameters to adapt TCP to wireless environments?

8. State the requirements of WAP.

9. Name the layers of WAP.

10. Name some ICMP messages.

11. What is WTP? What are its classes?

12. What is WSP?

13. Name some features of WSP adapted to web browsing.

14. What is WML?

15. What are the features of WML?

16. What are the advantages of WML Script over WML?

17. Name the libraries specified by WMLScript.

18. What are the classes of libraries?

19. Name the operations performed by PAP.

20. What are the components of WAP2.0?

Part-B

1. Explain traditional TCP. (16)

2. Explain classical TCP improvements (16)

3. Write short notes on WAP (16)

IT1402 Mobile Computing 1

UNIT-1

WIRELESS COMMUNICATION FUNDAMENTALS

PART – A (2MARKS) 1. What are the 3 fundamental propagation behaviors depending on their

frequency?

2. What is multipath propagation?

3. What is guard space?

4. What is the 3 different basic schemes analog modulation?

5. What is the use of Phase Lock Loop (PLL)?

6. What is hopping sequence?

7. What is dwell time?

8. What are the advantages of cellular systems?

9. What is browsing channel allocation and fixed channel allocation?

10. What are the disadvantages of cellular systems?

11. What is digital sense multiple access?

12. What is Network and Switching subsystem?

13. What is authentication centre?

14. What is called burst and normal burst?

15. What are the basic groups of logical channels?

16. Define traffic multi frame and control multi frame?

17. What is OVSF?

18. Specify the steps perform during the search for a cell after power on?

19. Explain about transparent mode?

20. What are the basic classes of handovers?

21. When are tuning frequency and frequency considered?

22. How can you utilize mobile antennas efficiently?

23. Compare various modulation techniques.

24. Define the relation between the data rate and bandwidth. What has harmonics to do with bandwidth?

PART – B

1. Discuss briefly the multiplexing techniques. (16)

2. Explain about the signal propagation. (16)

3. Discuss about the cellular system. (16)

4. List the difference between SDMA /TDMA /FDMA/CDMA. (16)

5. What is spread spectrum with its types. (16)

6. Explain about the TDMA. (16)

7. Why CDMA is needed and explain it with an example? (16)

8.

Why do MAC scheme in wired network fail in wireless networks and how does the multiple

access with collision avoidance (MACA) scheme work? (16)

9. Define modulation and explain the method for analog modulation techniques in details. (16)

10. Discuss briefly the code division multiplexing techniques. (16)

11. Discuss briefly the advanced phase shift keying. (16)

12.

a. Explain about cellular wireless network. (08)

b. Explain about wireless transmission. (08)

IT1402 Mobile Computing 2

13. Consider three users and Barker code of six bits each for the users transmitting the signals,

introduce noise and near / far problem while transmitting and reconstruct the data in the

receiving side providing the proper counter measures for the complications.

(16)

14. a.

Table the frequency bands used for wireless applications with their ranges, propagation

models and applications. (08)

b.

Represent diagrammatically the protocol machines for multiple access with collision

avoidance. (08)

UNIT- 2

TELECOMMUNICATION NETWORKS

PART – A (2 MARKS)

1. Specify the security services offered by GSM.

2. What is the frequency range of uplink and downlink in GSM network?

3. What are the two basic groups of logical channels in GSM? 4. What are the control channel groups in GSM?

5. List out the numbers needed to locate an MS and to address the MS.

6. What are the four possible handover scenarios in GSM?

7. What is meant by GGSN?

8. What is meant by SGSN?

9. What is meant by BSSGP?

10. Define the protocol architecture of DECT.

11. Specify the standards offered by TETRA.

12. How many ITU standardized groups of 3G radio access technologies are there in

IMT-2000?

13. What are the steps perform during the search for a cell after power on?

14. What are the two basic classes of handover?

15. What are the two basic transport mechanisms used by DAB?

16. What are the two transport modes defined for MSC?

17. Define the terms:

i. Earth Station.

ii. Uplink. 18. Define Elevation Angle.

19. What are the factors limited the number of sub channels provided within the

satellite channel?

20. Differentiate Broadcast from Multicast.

21. Detail the features of MSAT.

22. How can an efficient routing be made in satellite systems? 23. What do you understand by co channel interference and adjacent?

24. Describe the services provided by GSM network.

PART – B

1. Explain GSM architecture. (16)

2. Explain Satellite networks in detail. (16)

3. Write short notes on DAB. (16)

4. Write short notes on DVB. (16)

5. Explain DECT. (16)

6. Explain in details the functioning of GPRS. (16)

7. Compare GEO, MEO and LEO (16)

IT1402 Mobile Computing 3

8. Sketch the data network in your campus. How many hosts are there and how large is

the user population? What is the speed of the access link to the Internet? How so you

gain access to the Internet? How much does home access to the Internet costs?

(16)

9.

a.

Consider a mobile user who is migrating from a place to another place provide him a

seamless service by satellite system, also sketch the architecture. (08)

b. Discuss the importance of DECT Protocol Layers. (08)

UNIT-3

WIRELESS LAN

PART – A (2 MARKS)

1. What are the advantages of WLANS? 2. Mention some of the disadvantages of WLANS. 3. Mention the design goals of WLANS. 4. What is the difference between infrastructure and ad-hoc networks? 6. Mention the features of infrared transmission. 7. What are the disadvantages of infrared transmission? 8. Mention the features of radio transmission. 9. What are the disadvantages of radio transmission? 10. Define frequency hopping spread spectrum. 11. Define random back off time. 12. What is Traffic Indication Map? 13. What is Delivery Traffic Indication Map? 14. What is Ad-hoc TIM? 15. What is meant by roaming? 16. Mention the features of HIPERLAN1. 17. What are the three phases of medium access in EY-NPMA? 18. Mention the elements of Bluetooth core protocols. 19. What is the purpose of sniff state? 20. What is the use of hold state? 21. What is the purpose of park state? 22. In what functionality Switches differ from Routers. PART – B

1. Explain the architecture and features of IEEE 802.11 in details. (16)

2. Explain the MAC layer in IEEE802.11. (16)

IT1402 Mobile Computing 4

3. Explain HIPERLAN in detail. (16)

4. Write short notes on Bluetooth. (16)

5. Explain the service offered by IEEE802.11 standard. (16)

6. Explain how power management is done in IEEE 802.11 infrastructure

based and ad hoc networks. (16)

7. Discuss how to increase the quality of service in an ad hoc network. (16)

8. a. Detail the time- bounded service on top of the standard DCF

mechanism where ad hoc networks cannot use the function. (08)

b. Discuss the PHY frame format of an IEEE 802.11 using the spread

spectrum technique which separates by code. (08) 9. a. The channel access control sublayer of HIPERLAN offers a connectionless

data transfer service to the higher MAC layer. Justify

the above statement with related references. (08)

b.Discuss the functionalities and support provided by L2CAP. (08)

UNIT - 4

MOBILE NETWORK LAYER

PART – A (2 MARKS)

1. What are the requirements of mobile IP?

2. Mention the different entities in a mobile IP.

3. What do you mean by mobility binding?

4. Define a tunnel.

5. What is encapsulation?

6. What is decapsulation?

7. Define an outer header

8. Define an inner header.

9. What is meant by generic routing encapsulation?

10. What is the use of network address translation?

11. Define triangular routing.

12. What is meant by a binding cache?

13. Define binding request.

14. What is known as Binding update?

15. Explain binding acknowledgement.

16. Define binding warning.

17. Explain cellular IP.

IT1402 Mobile Computing 5

18. What are the advantages of cellular IP? 19. What is known as mobility anchor point? 20. Explain destination sequence distance vector routing. 21. What are the two things added to the distance vector algorithm? 22. How the dynamic source routing does divide the task of routing into two

separate problems?

PART – B

1. a. What are the requirements of a mobile IP? (08)

b. Describe Dynamic host configuration protocol. (08)

2. a. Discuss the routing algorithm in ad-hoc network. (08)

b. What are the entities in mobile IP? (08)

3. a. Discuss how optimization in achieved in mobile IP. (08)

b. Explain tunneling and encapsulation in mobile IP. (08)

4. Explain how dynamic source routing protocols handles routing with an

example. (16)

5. Discuss and detail the differences in topology reorganization in DSDV

and DSR routing protocols. (16)

6. a. What are the general problems of mobile IP regarding security and

support of quality of service? (08)

b. Name the inefficiencies of mobile IP regarding data forwarding from a

correspondent node to a mobile node. What are optimizations and what

additional problems do they cause? (08)

UNIT- 5

TRANSPORT AND APPLICATION LAYERS

PART – A (2 MARKS) 1. What is slow start? 2. What is the use of congestion threshold? 3. What led to the development of Indirect TCP? 4. What is the goal of M-TCP? 5. What do you mean by persistent mode? 6. What are the characteristics of 2.5G/3.5G wireless networks? 7. What are the configuration parameters to adapt TCP to wireless

environments? 8. State the requirements of WAP.

9. Name the layers of WAP. 10. Name some ICMP messages. 11. What is WTP? What are its classes?

IT1402 Mobile Computing 6 12. What is WSP? 13. Name some features of WSP adapted to web browsing. 14. What is WML? 15. What are the features of WML? 16. What are the advantages of WML Script over WML? 17. Name the libraries specified by WML Script. 18. What are the classes of libraries? 19. Name the operations performed by PAP. 20. What are the components of WAP2.0? 21. How and why does I-TCP isolate problems on the wireless link?

PART – B

1. Explain in detail about traditional TCP in details. (16)

2. Explain classical TCP improvements and snooping TCP. (16)

3. Explain the function of the components of the WAP architecture. (16)

4. Explain the concept of wireless markup language. (16)

5. Explain wireless application protocols with the it’s version WAP 2.0 in

detail. (16)

6. Describe the operation of the window flow control mechanism. (16)

7. What are the major difference between WAP 2.0 and WAP 1.x? What

influenced the WAP 2.0 development? (16)

Model Exam1

Subject Name : Mobile Computing Max. Marks: 100 Duration : 3 Hrs

Answer all the questions

PART –A (10 x 2 = 20 Marks)

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

2. What are main benefits of spread spectrum system?

3. What are the reasons for delays in GSM for packet data traffic?

4. Differentiate hard and soft handoff.

5. Why is the physical layer in IEEE 802.11 subdivided?

6. What is HIPERLAN?

7. What are the differences between AODV and standard distance vector algorithm?

8. What advantages does the use of IPV6 offer for mobility?

9. How does I-TCP isolate problems on wireless link?

10. List out the advantages of WAP.

PART-B (5 x 16 = 80 Marks)

11. (a) Explain in detail about multiplexing. (16)

(OR)

(b) Sketch the block diagram of transmitter and receiver of DSSS & FHSS. (16)

12. (a) Explain the functional and protocol architecture of GSM. (16)

(OR)

(b) Discuss the functional and protocol architecture of GPRs. (16)

13. (a) (i) Explain IEEE 802.11 protocol architecture and bridging with

other networks. (10)

(ii) How do IEEE 802.11 solve hidden terminal problems? Explain

With necessary diagrams. (6)

(OR)

(b) Discuss in detail about Bluetooth. (16)

14. (a) Explain any one reactive routing protocol in ad-hoc networks with an (16)

example.

(OR)

(b) Discuss ZRP and ODMR in detail. (16)

(OR)

15. (a) Compare and contrast I-TCP, Snooping TCP and M-TCP. (16)

(OR)

(b) Discuss briefly about WAP architecture.

Model Exam2

Subject Name : Mobile Computing Max. Marks: 100 Duration : 3 Hrs

Answer all the questions

PART –A (10 x 2 = 20 Marks)

1. Differentiate analog modulation and digital modulation.

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

3. What are the reasons for delays in GSM for packet data traffic?

4. How security is implemented in GSM?

5. Why is the physical layer in IEEE 802.11 subdivided?

6. What is DCF?

7. What are the differences between AODV and standard distance vector algorithm?

8. What advantages does the use of IPV6 offer for mobility?

9. Define fast retransmit.

10. What are the classes in WTP?

PART-B (5 x 16 = 80 Marks)

11. (a) Compare and contrast S/T/F/CDMA in detail. (16)

(OR)

(b) Explain in detail about spread spectrum techniques. (16)

12. (a) Explain the functional and protocol architecture of GSM. (16)

(OR)

(b) Discuss channel allocation and call routing in detail. (16)

13. (a) (i) Explain IEEE 802.11 MAC functions in detail. (10)

(ii) How do IEEE 802.11 solve hidden terminal problems? Explain

With necessary diagrams. (6)

(OR)

(b) Discuss in detail about HIPERLAN. (16)

14. (a) Explain the following with respect to IP.

(i) Agent Advertisement.

(ii) Tunneling.

(iii) Encapsulation.

(OR)

(b) Discuss about DSDV and DSR. (16)

(OR)

15. (a) Explain the TCP improvement techniques in detail. (16)

(OR)

(b) Discuss briefly about WTLS, WSP and WAE in WAP. (16)

Model Exam3

Subject Name : Mobile Computing Max. Marks: 100 Duration : 3 Hrs

Answer all the questions

PART –A (10 x 2 = 20 Marks)

1. What are the several versions in CSMA?

2. What is FDD?

3. What are types of Handover?

4. What is meant by beacon?

5. What are the advantages and disadvantages of infrared?

6. .What is the differences between AODV and standard distance vector algorithm?

7. What advantages does the use of IPV6 offer for mobility?

8. What are the requirements for the development of mobile IP?

9. Define slow start.

10. Define wml.

PART-B (5 x 16 = 80 Marks)

11. (a) Discuss signal propagation techniques in detail. (16)

(OR)

(b) Explain in detail about spread spectrum techniques. (16)

12. (a) Explain channel allocation and call routing in GSM. (16)

(OR)

(b) Discuss functional and protocol architecture of GPRs. (16)

13. (a) Explain in detail about Bluetooth. (16)

. (OR)

(b) Discuss in detail about HIPERLAN. (16)

14. (a) Explain the following with respect to IP.

(i) Agent Registration.

(ii) IP optimization.

(iii) Tunneling.

(OR)

(b) Discuss about DHCP in detail. (16)

15. (a) Explain I-TCP,M-TCP,S-TCP and Freezing TCP in detail. (16)

(OR)

(b) Discuss briefly about WAP architecture. (16)

Question paper code: D2286

B.E/B.Tech Degree Examination APRIL /MAY 2010

Eighth Semester

Computer Science and Engineering

IT1402-MOBILE COMPUTING

(Regulation 2004)

Answer all questions

Part -A(10*2=20)Marks

1 What is spreading factor?

2.What is polling?

3.Distinguish between soft handover& hard Hand over.

4.Define foot print with respect to satellite systems.

5.State the 3 phases of the medium access of different competing nodes.

6.what are the power saving mechanisms in bluetooth?

7.What are the drawbacks of wired networks?

8.Define Dynamic Source Routing.

9.What is the difference between TCP & UDP.

10. Mention any 2 salient features of WAP.

Part-B (5*16=80)Marks

11 (a) i Discuss in detail about the types of antennas with their radiation patterns.(12)

ii Explain Diversity techniques.(4)

[or]

11 (b) Explain space Frequency,code & Time division Multiplexing in detail.(16)

12 (a) Describe Digital Audio Broadcasting.(16)

[or]

(b) Explain routing ,localization and handover in satellite systems.(16)

13 (a) Describe architecture of BLUE TOOTH.(16)

[or]

(b)Explain Channel control sub layer in HIPERLAN.(16)

14 (a) Explain optimization in Mobile IP in detail.(16)

[or]

(b)Explain IPV6 Protocol in detail.(16)

15 (a) Discuss the role of WWW in support for mobility.(16)

[or]

(b) Explain the following:

(i) Indirect TCP. (6)

(ii)Snooping TCP.(6)

(iii)Explain about performance enhancing proxies.(4)

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2009.

Seventh Semester

Information Technology

IT1402- MOBILE COMPUTING

(Regulation 2004)

Time: Three hours Maximum:100 marks

Answer ALL questions.

PART A- (10 X 2= 20 Marks)

1. Why do Hidden and Exposed terminal problems arise?

2. Differentiate Broadcast from Multicast.

3. Detail the features of MSAT.

4. How can an efficient routing be made in satellite systes?

5. When are tuning frequency and frequency considered?

6. How can you utilize mobile antennas efficiently?

7. Compare various modulation techniques.

8. When it's required to go for GMSK, GFSK and DQPSK?

9. In what functionalities Switches differ from Routers?

10. How and why does I-TCP isolate problems on the wireless link?

PART B - (5 X 16 = 80 Marks)

11. (a) Consider three users and Barker code of six bits each for the users transmitting

the signals, introduce noise and near/far problem while transmitting and reconstruct

the data in the receiving side providing the proper countermeasures for the

complications. (Note: Use CDMA technologies) (Marks 16)

(Or)

(b) (i) Table the frequency bands useed for wireless applications with their ranges,

propagation models and applications. (Marks 6)

(ii) Represent diagrammatically the protocol machines for multiple access with

collision avoidance. (Marks 10)

12. (a) (i) Sketch the data network in your campus. How many hosts are there and

how large is the user population? What is the speed of the access link to the Internet?

How so you gain access to the Internet? How much does home access to the Internet

costs? (Marks 10)

(ii) Why are so many different identifiers/addresses (e.g. MSISDN, TMSI, IMSI)

needed in GSM? Give reasons and distinguish between user- related and system

related identifiers. (Marks 6)

(Or)

(b) (i) Consider a mobile user who is migrating from a place to another place, provide

him a seamless service by satellite system, also sketch the architecture. (Marks 8)

(ii) Discuss the importance of DECT Protocol Layers. (Marks 8)

13. (a) (i) Detail the time- bounded service on top of the standard DCF mechanism

where ad hoc networks cannot use the function. (Marks 8)

(ii) Discuss the PHY frame format of an IEEE 802.11 using the spread spectrum

technique which separates by code. (Marks 8)

(Or)

(b) (i) The channel access control sublayer of HIPERLAN offers a connectionless

data transfer service to the higher MAC layer. Justify the above statement with related

references. (Marks 10)

(ii) Discuss the functionalities and support provided by L2CAP. (Marks 6)

14. (a) Discuss and detail the differences in topology reorganization in DSDV and

DSR routing protocols. (Marks 16)

(Or)

(b) (i) What are the general problems of mobile IP regarding security and support of

quality of service? (Marks 8)

(ii) Name the inefficiencies of mobile IP regarding data forwarding from a

correspondent node to a mobile node. What are optimizations and what additional

problems do they cause? (Marks 8)

15. (a) What are the major difference between WAP 2.0 and WAP 1.x? What

influenced the WAP 2.0 development? (Marks 16)

(Or)

(b) Detail about UTMS Radio Interfaces in Frequency Division Duplex and Time

Division Duplex modes. (Marks 16)

MAY /JUNE 2009

MOBILE COMPUTING.

Part –A

1. Define near /far effect?

2. Give any two application of satellite systems?

3. What are ad-hoc networks?

4. Define handover in WATM?

5. What is meant by Registration lifetime of a packet ?

6. What is meant by tunneling?

7. How does the standard TCP behave when a packet is lost during transmission?

8. Define time – out freezing?

9. Mention the role of transaction layer in WAP?

10. Mention any two messages of WCMP?

Part –B

11. a)Explain in detail:

i)DECT system. [Mark 8]

ii)TETRA system. [Mark 8]

Or

b) i) Discuss LEO,MEO, and GEO satellite systems. [Mark 8]

ii) Discuss Digital Video Broadcasting. [Mark 8]

12. a )Explain in detail:

i)HIPERLAN [Mark 8]

ii) BLUETOOTH [Mark 8]

Or

b) What is meant by WATM? Describe WATM reference model, location management ,

services and QOS. [Mark 16]

13.a) i) Discuss the purpose and application of DHCP. [Mark 8] ii) Explain agent

discovery and registration. [Mark 8]

Or

b) Explain the various routing strategies in mobile ad-hoc networks?

14. a) Explain any 4 classical TCP improvement techniques. [Mark 16]

Or

b) i)Discuss Transaction oriented TCP in detail. [Mark 8]

ii) Discuss TCP over 2.5/3G wireless networks. [Mark 8]

15.a) Discuss the component of WAP arch/- and its application environment. [Mark 16]

Or

b)i)Write short notes on WML script. [Mark 8]

ii) Discuss WTA? [Mark 8]

B.E. / B.Tech DEGREE EXAMINATION, NOVEMBER/DECEMBER 2008

Seventh Semester

Information Technology

IT1402 – MOBILE COMPUTING

(Regulation 2004)

Time: Three hours Maximum: 100 marks

Answer ALL questions.

PART A – (10 x 2=20 marks)

1. Differentiate analog modulation and digital modulation.

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

3. What are the general problems of satellite signals travelling from a satellite to

receiver?

4. Differentiate symmetrical and asymmetrical communication system.

5. What is HIPERLAN?

6. How is mobility restricted using WLANS?

7. What could be quick ‘solutions’ and why don’t they work?

8. What advantages does the use of IPV 6 offer for mobility?

9. Write the advantages and disadvantages of mobile TCP.

10. Define fast retransmit.

PART B – (5 x 16 = 80 marks)

11. (a) Explain in detail about multiplexing.

Or

(b) Explain the following :

(i) MAC

(ii) SDMA.

12. (a) Explain the functional architecture of a GSM system.

Or

(b) Discuss about digital video broadcasting.

13. (a) Explain the concept of blue tooth architecture.

Or

(b) Explain the concept of IEEE 802.11 medium access control layer.

14. (a) Explain the following :

(i) DSDV [Marks 8]

(ii) Ad-hoc DSR. [Marks 8]

Or

(b) Discuss about tunneling and encapsulation mechanism and reverse tunneling.

15. (a) Explain and detail about traditional TCP.

Or

(b) (i) Briefly explain about indirect and snooping TCP. [Marks 8]

(ii) Briefly discuss about WAP.[Marks 8]

B.E/B.Tech. Degree Examination, April/May 2008

Eighth Semester

(Regulation 2004)

Computer Science and Engineering

IT 1402- Mobile Computing

Part-A(10*2=20 marks)

1. Assume a receiver is located 10 km from a 150 W transmitter. The carrier

frequency is 6 GHz and free space propagation is assumed, Gain at

transmitter is 1 dB and Gain at receiver is 1 dB.

(a) Calculate the transmit power in dBW.

(b) Find the power at the receiver in Watts.

2. What limits the number of simultaneous users in a TDM/FDM system compared

to a CDM system ? What happens to the transmission quality of connections

if the load gets higher on the cell ?

3. Consider the handoff procedure in GSM system that is based on relative

signal strength with threshold; that is, a mobile switches from one cell

to another if (a) the signal at the current BS is sufficiently weak (less

than a predefined threshold) and (b) the other signal is stronger than

the two. What are the drawbacks of this scheme, when the threshold is

too low or too high ?

4. State the different types of transport modes and channels used to carry

packets in Digital Audio Broadcasting.

5. In the Distributed Coordination Function(DCF) protocol of IEEE 802.11,

why does a Node wait only SIFS time units (after the last data packet

reception) before sending an ACK, while waiting DIFS time units before

attempting a data transmission ?

6. What are the advantages and problems of forwarding mechanisms in Bluetooth

networks regarding security and power saving ?

7. How can DHCP be used for mobility and support of Mobile IP ?

8. What are the differences between AODV and the standard distance vector

algorithm ? Why are extensions needed ?

9. How and why does I-TCP isolate problems on the wireless link ? What are

the main drawbacks of this solution ?

10.Mention two WAP service providers. Find two cell phones supporting WAP

and identify which WAP version they support.

Part-B(5*16=80 marks)

11. (a) How does frequency reuse enhance cellular network capacity ? Besides

the number of users, what other major factor influences the decision

on cluster size ? A cellular system uses frequency spectrum 1800 MHz

to 1840 MHz for uplink channels and 1860 MHz to 1900 MHz for downlink

channels respectively. Each channel takes 200 KHz and can be shared

by 8 users. Each user needs one uplink and one downlink channel. How

many users can be supported without frequency reuse in this cellular

system ? [16]

(OR)

(b) What is the use of spread spectrum ? Sketch the block diagram of the

Transmitter and Receiver of DSSS. Explain what each block does and

what the signal looks like (in time and/or frequency domains) at each

location in the block diagram with an example.[16]

12. (a) Name the main elements of GSM system architecture and describe their

functions. What are the advantages of specifying not only the radio

interface but also the internal interfaces of the GSM system ?

Explain the inter-BSC,intra-MSC handover process in the GSM system

using typical signals and a message sequence chart. Explain the

decision points and the resource allocation steps,if they exist.[16]

(OR)

(b) What is DAB ? Explain the components,frame format and the protocol

used by DAB to access different formats of data also describe how

DVB is used for data broadcasting and to access high speed internet.

[16]

13. (a) (i) Using IEEE 802.11 (DCF): S1 and S2 send CBR/UDP traffic to the

common destination D. Consider S1,S2 and D all within receive

range of each other when the basic scheme is used (no RTS/CTS):

Describe a collision (what happens before,during and after).What

does the collision probability depend on ? When RTS/CTS is used:

What are the changes to the previous answers ? comment also on

the throughput and fairness. [16]

(OR)

(b) (i) Describe the briefly how collision is avoided in HIPERLAN-1. [8]

(ii)Draw the protocol architecture of Bluetooth and explain briefly

the Base band layer and L2CAP of Bluetooth. [8]

14. (a) Given the network topology below, use the dynamic source routing

algorithm to compute the shortest path from A to all other nodes.

Make sure to show the results of the computation at each step.[16]

7

B --- D

|\ 1/ |

| \ / |

12| /\ |1

| /10\ |

A --- C -------- E

3 1

(OR)

(b) Consider a mobile node MN from network X. The user of MN wishes to

communicate with a corresponding node CN in network Y. The node MN

moves from X to a foreign network A. Describe the sequence of

messages that are required in Mobile IPv4 so that MN and CN can

continue to communicate. Include both the user data messages and the

Mobile IP control messages. Now, consider the case where CN moves to

foreign network B while MN is still in the foreign network A. Can

CN and MN still communicate ? (Does Mobile IP support both endpoints

moving? ) Show the message flow to indicate how it will succeed or

fail in this case. [16]

15. (a) As a transport layer protocol, TCP uses a window mechanism to

exercise flow control over the best effort IP in the internet.

Flow control is exercised by the edge router based on congestion

status encountered in the core routers between teh TCP sender and

TCP receiver.

(i) Describe the operation of the window flow control mechanism. [8]

(ii)ACKs from the TCP receiver are the basis that the TCP sender

uses to adjust the sending window size. Describe and discuss

how ACKs are used for this purpose. [8]

(OR)

(b) Specify the enhancements made to the basic client server architecture

of the web to suit a mobile wireless user ? Briefly discuss the main

goals of WAP. Expain the layers of WAP protocol used to achieve the

following : A client wants to have a shared state with the server

for transferring the content. [16]

DEGREE EXAMINATION

MOBILE COMPUTING

Time : Three Hours Maximum : 100 marks

PART A (10 x 2 = 20 marks)

1. What is a guard space?

2. What is CMDA?

3. List the four possible handover and scenarios in GSM

4. Define inclination angle and elevation angle

5. Give the 802.11 PHY frame format using DSS

6. What are the low power states of a blue tooth device?

7. What is a care of address?

8. What are the routing metrics in wireless adhoc network?

9. What is a wireless Telephony application?

10. List the classes of transaction service of WTP.

PART B (5 x 16 = 80 marks)

11. (a) Discuss in detail the Wireless Transaction Protocol. (16)

(or)

(b) Discuss in detail the Wireless Session Protocol (16)

12. (a) Explain time division multiple access (16)

(or)

(b) (i) Discuss the spread spectrum techniques (10)

(ii) What is Code Division Multiplexing? Explain (6)

13. (a) (i) Discuss in detail localization, calling and handover in GSM (10)

(ii) Explain the types of orbits in satellite system (6)

(or)

(b) (i) Explain the GSM system architecture (12)

(ii)Explain the protocol architecture of DECT (4)

14. (a) Discuss in detail the medium access control mechanism of ICCC 802.11 (16)

(or)

(b) (i) Explain the information bases and networking of adhoc HIPERLAN. (8)

(ii) Discuss MAC layer bluetooth system (8)

15. (a) (i)Describe tunneling and encapsulation in Mobile IP (8)

(ii) Discuss in detail dynamic source routing (8)

(or)

(b) (i) Write short notes on reverse tunneling (4)

(ii) Explain IP packet delivery, agent advertisement, discovery and registration process in

mobile IP (12)

DEGREE EXAMINATION

MOBILE COMPUTING

Time : Three Hours Maximum : 100 marks

PART A- (10x2=20 marks)

1. What is spreading factor?

2. What is polling?

3. Distinguish between soft hand over and hard hand over.

4. Define footprint with respect to satellite systems.

5. State the three phases of the medium access of different competing nodes.

6. What are the power saving mechanisms in Bluetooth?

7. What are the drawbacks of wired networks?

8. Define: Dynamic Source Routing.

9. What is the difference between TCP and UDP?

10. Mention any two salient features of WAP.

PART B- (5x16=80 marks)

11.(a)(i) Discuss in detail the types of Antennas with their radiation patterns.

(ii) Explain Diversity techniques.

OR

(b) Explain Space, Frequency, Code and Time Division multiplexing in detail.

12.(a) Describe Digital Audio Broadcasting.

OR

(b) Explain routing, localization and hand over in satellite systems.

13.(a) Describe the architecture of BLUE TOOTH.

OR

(b) Explain channel control sub layer in HIPERLAN.

14.(a) Explain optimization in Mobile IP in detail.

OR

(b) Explain IPv6 protocol in detail.

15.(a) Discuss the role of WWW in support for mobility.

OR

(b) Explain the following:

(i) Indirect TCP.

(ii) Snooping TCP.

(iii) Explain about performance enhancing proxies.