A Course Material on

MOBILE COMPUTING

By

Mr. D.PRABHAKARAN

ASSISTANT PROFESSOR

DEPARTMENT OF INFORMATION TECHNOLOGY & COMPUTER APPLICATIONS

SASURIE COLLEGE OF ENGINEERING

VIJAYAMANGALAM – 638 056

QUALITY CERTIFICATE

This is to certify that the e-course material

Subject Code : YCS012

Scubject : MOBILE COMPUTING

Class : III B.sc CT (COMPUTER TECHNOLOGY)

being prepared by me and it meets the knowledge requirement of the university curriculum.

Signature of the Author

Name:

Designation:

This is to certify that the course material being prepared by Mr.D.Prabhakaran is of adequate quality. He has referred more than five books amont them minimum one is from aborad author.

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YCS012 MOBILE COMPUTING L T P C3 0 0 3

UNIT I WIRELESS COMMUNICATION FUNDAMENTALS 9

Introduction – Wireless transmission – Frequencies for radio transmission – Signals – Antennas– Signal Propagation – Multiplexing – Modulations – Spread spectrum – MAC – SDMA – FDMA– TDMA – CDMA – Cellular Wireless Networks.

UNIT II TELECOMMUNICATION NETWORKS 9

Telecommunication systems – GSM – GPRS – DECT – UMTS – IMT-2000 – Satellite Networks- Basics – Parameters and Configurations – Capacity Allocation – FAMA and DAMA –Broadcast Systems – DAB - DVB.

UNIT III WIRLESS LAN 9Wireless LAN – IEEE 802.11 - Architecture – services – MAC – Physical layer – IEEE 802.11a -802.11b standards – HIPERLAN – Blue Tooth.

UNIT IV MOBILE NETWORK LAYER 9Mobile IP – Dynamic Host Configuration Protocol - Routing – DSDV – DSR – AlternativeMetrics.

UNIT V TRANSPORT AND APPLICATION LAYERS 7Traditional TCP – Classical TCP improvements – WAP, WAP 2.0.

TOTAL : 45

REFERENCE BOOKS:1. Jochen Schiller, “Mobile Communications”, PHI/Pearson Education, Second Edition, 2003.(Unit I Chap 1,2 &3- Unit II chap 4,5 &6-Unit III Chap 7.Unit IV Chap 8- Unit V Chap 9&10.)2. William Stallings, “Wireless Communications and Networks”, PHI/Pearson Education, 2002.(Unit I Chapter – 7&10-Unit II Chap 9)3. Kaveh Pahlavan, Prasanth Krishnamoorthy, “Principles of Wireless Networks”, PHI/PearsonEducation, 2003.4. Uwe Hansmann, Lothar Merk, Martin S. Nicklons and Thomas Stober, “Principles of MobileComputing”, Springer, New York, 2003.

YCS012 -MOBILE COMPUTING

UNIT I

WIRELESS COMMUNICATION FUNDAMENTALSIntroduction – Wireless transmission – Frequencies for radio transmission – Signals – Antennas – SignalPropagation – 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 computingWireless 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 environmento 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 operationo 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

2

APPLICATIONS

Vehiclestransmission of news, road condition, weather, music via DABpersonal communication using GSMposition via GPSlocal ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancyvehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance

Emergenciesearly transmission of patient data to the hospital, current status, first diagnosisReplacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc.crisis, war, ...

Travelling salesmendirect access to customer files stored in a central locationconsistent databases for all agentsmobile office

Replacement of fixed networksremote sensors, e.g., weather, earth activitiesflexibility for trade showsLANs in historic buildings

Entertainment, education,outdoor Internet accessintelligent travel guide with up-to-date location dependent informationad-hoc networks for multi user games

Location dependent services

Location aware serviceswhat services, e.g., printer, fax, phone, server etc. exist in the local environment

Follow-on servicesautomatic 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 servicescaches, intermediate results, state information etc. „follow“ the mobile device through the fixednetwork Privacywho should gain knowledge about the location

Effects of device portability

Power consumptionlimited computing power, low quality displays, small disks due to limited battery capacityCPU: power consumption ~ CV2f

3

Loss of data

• C: internal capacity, reduced by integration• V: supply voltage, can be reduced to a certain limit• f: clock frequency, can be reduced temporally

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

Limited user interfacescompromise between size of fingers and portabilityintegration of character/voice recognition, abstract symbols

Limited memorylimited value of mass memories with moving partsFlash-memory or? as alternative

Wireless networks in comparison to fixed networks

Higher loss-rates due to interferenceemissions of, e.g., engines, lightning

Restrictive regulations of frequenciesfrequencies have to be coordinated, useful frequencies are almost all occupied Low transmissionrates

local some Mbit/s, regional currently, e.g., 9.6kbit/s with GSM .Higher delays, higher jitterconnection setup time with GSM in the second range, several hundred milliseconds for otherwireless systems

Lower security, simpler active attackingradio interface accessible for everyone, base station can be simulated, thus attracting calls frommobile phones

Always shared mediumsecure 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 inductionJ. Maxwell (1831-79): theory of electromagnetic Fields, wave equations (1864)H. Hertz (1857-94): demonstrateswith an experiment the wave character of electrical transmissionthrough space(1886, in Karlsruhe, Germany, at the location of today’s University of Karlsruhe)

4

Wireless systems: overview of the development

cellular phones

1981:NMT 450

1983:

1986: AMPSNMT 900

1991: 1991:CDMA D - AMPS

1992:GSM

1993:PDC

1994:DCS 1800

analog

satellites

1982:Inmarsat - A

1988:Inmarsat - C

1992:Inmarsat - BInmarsat - M

1998:Iridium

cordlessphones

1980:CT0

1984:

CT1

1987:

CT1+

1989:CT 2

1991:DECT

wirelessLAN

199x:

proprietary

1995/96/97:IEEE 802.11,HIPERLAN

2005?:

digital2005?:

UMTS/IMT - 2000MBS, WATM

Areas of research in mobile communication

Wireless Communicationtransmission quality (bandwidth, error rate, delay)modulation, coding, interferencemedia access, regulations

Mobilitylocation dependent serviceslocation transparencyquality of service support (delay, jitter, security)

Portabilitypower consumptionlimited computing power, sizes of display, ...usability

5

Simple reference model used here

Application

Transport

Application

Transport

Network

Data Link

Physical

Radio

Network

Data Link

Physical

Network

Data Link

Physical

Medium

Network

Data Link

Physical

Influence of mobile communication to the LAYER MODEL

Application layer

service locationnew applications, multimediaadaptive applications

Transport layer

congestion and flow controlquality of service

Network layer

addressing, routing, device locationhand-over

Data link layer

authenticationmedia accessmultiplexingmedia access control

6

Physical layer

encryptionmodulationinterferenceattenuationfrequencyWIRELESS TRANSMISSION - FREQUENCIES FOR RADIO TRANSMISSION

Frequencies for communication

twisted coax cablepair

optical transmission

1 Mm300 Hz

VLF

10 km30 kHz

LF

100 m3 MHz

MF HF

1 m300 MHz

VHF UHF

10 mm30 GHz

SHF EHF

100 m3 THz

infrared

1 m300 THz

visiblelight

UV

• VLF = Very Low Frequency• LF = Low Frequency• MF = Medium Frequency• HF = High Frequency• VHF = Very High Frequency

• Frequency and wave length:

= c/f

UHF = Ultra High FrequencySHF = Super High FrequencyEHF = Extra High FrequencyUV = Ultraviolet Light

• wave length , speed of light c 3x108m/s, frequency f

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 RadioConferences)

7

Mobilephones

Cordlesstelephones

Europe

NMT 453 - 457MHz,463 -467 MHz; GSM 890 -915 MHz,935 -960 MHz; 1710 - 1785 MHz,1805 - 1880 MHz CT1+ 885 - 887 MHz,930 -932 MHz; CT2

USA

AMPS , TDMA , CDMA824 -849 MHz,869 -894 MHz; TDMA , CDMA , GSM1850 - 1910 MHz, 1930 - 1990 MHz; PACS 1850 - 1910 MHz,1930 - 1990 MHz PACS - UB 1910 - 1930 MHz

Japan

PDC810 -826 MHz,940 -956 MHz;1429 - 1465 MHz, 1477 - 1513 MHz

PHS1895 - 1918 MHz JCT

864 -868 MHz DECT

254 -380 MHz

W ireless LANs

1880 - 1900 MHz IEEE 802.112400 - 2483 MHz

IEEE 802.112400 - 2483 MHz

IEEE 802.112471 - 2497 MHz

physical representation of datafunction of time and location

SIGNALS

signal parameters: parameters representing the value of data

classificationo continuous time/discrete timeo continuous values/discrete valueso analog signal = continuous time and continuous valueso digital signal = discrete time and discrete values

signal parameters of periodic signals:period T, frequency f=1/T, amplitude A, phase shift j

sine wave as special periodic signal for a carrier:

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

Fourier representation of periodic signals

g t( )

1 �

c �a

n sin( 2�nft )

�

�b

n cos( 2�nft )

8

2 n 1 n 1

1

0

Ideal periodic signalt

1

0

Real composition (harmonics )

based ont

Different representations of signals

amplitude (amplitude domain)frequency spectrum (frequency domain)phase state diagram (amplitude M and phase j 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 transmissionIsotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antennaReal antennas always have directive effects (vertically and/or horizontally)Radiation pattern: measurement of radiation around an antenna

Ideal isotropic radiator

9

y

Simple dipoles

z

xy

z

x

Real antennas are not isotropic radiators but, e.g., dipoles with lengths l/4 on car roofs or l/2 as Hertzian dipole,shape of antenna proportional to wavelength

/4

Example: Radiation pattern of a simple Hertzian dipole

10

/2

• Real antennas are not isotropic radiators but, e.g., dipoles wit h lengths /4 on carroofs or /2 as Hertzian dipole

/4

shape of antenna proportional to wavelength

/2

• Example: Radiation pattern of a simple Hertzian dipoley y

x z

z

xSimple dipole

side view ( xy - plane) side view ( yz - plane ) top view ( xz - plane)

• Gain: maximum power in the direction of the main lobe compared tthe power of an isotropic radiator (with the same average power)

Directed and Sectorized

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

o

y

side view ( xy-plane)

z

x

y

side view ( yz-plane)

z

z

z

top view ( xz-plane)

xDirected antenna

11

top view, 3 sector

x

top view, 6 sector

x Sectorized antenna

Antennas: diversity

Grouping of 2 or more antennaso multi-element antenna arrays

Antenna diversityo switched diversity, selection diversity

receiver chooses antenna with largest outputdiversity combining

combine output power to produce gaincophasing needed to avoid cancellation

/2 /2

/4

+

/4 /2

+

Transmission range

Detection range

Interference range

12

SIGNAL PROPAGATION

communication possiblelow error rate

detection of the signal possibleno communication possible

signal may not be detectedsignal adds to the background noise

Signal propagation

Sender

Transmission

Detection

Interference

Distance

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)shadowingreflection at large obstaclesscattering at small obstaclesdiffraction at edges

13

Shadowing

Multipath propagation

Reflection Scattering Diffraction

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

Time dispersion: signal is dispersed over time

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

The signal reaches a receiver directly and phase shifted

è Distorted signal depending on the phases of the different parts

Effects of mobility

Channel characteristics change over time and location

signal paths changedifferent delay variations of different signal partsdifferent phases of signal parts

èQuick changes in the power received (short term fading)

Additional changes indistance to senderobstacles further away

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

MULTIPLEXING

Multiplexing in 4 dimensionsspace (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 thatof the signals it has to carry. Each signal is modulated on a different carrier frequency. This results in shifting thespectrum of the signal around the carrier frequency. Sufficient guard-band is given so those neighboring signalsdo 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 demodulatingwith the same carrier frequency that was used to modulate the signal. The signals carried using FDM may beanalog signals or may be analog signals representing digital data. However FDM is mostly a technique from the

14

era of analog communications. In FDM a device uses some of the channel all of the time. FDM is used in radioand 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 .Receivercan "tune" to specific frequency and extract modulation for that one channel .Frequencies must be separated toavoid interference - “Wastes” potential signal bandwidth for guard channels.Only useful in media that can carrymultiple signals with different frequencies - high-bandwidth required .Used in:

The standard of the analog telephone networkThe standard in radio broadcastingThe standard for video

1. Broadcast2. Cable3. 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 ona communication link exceeds the data rate required by any one of the sources. In TDM each source that is touse the link fills up a buffer with data. A TDM multiplexer scans the buffers in some predetermined order andtransmits bits from each source one after the other.

Requires digital signaling & transmissionRequires data rate = sum of inputs + framingData rate much higher than equivalent analog bandwidth usesSeparates data streams in time not frequencyThe standard of the modern digital telephone system

15

Code Division Multiplexing - CDM

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

Advantages:

bandwidth efficientno coordination and synchronization necessarygood protection against interference and tapping

Disadvantages:

lower user data ratesmore complex signal regeneration

16

k1 k2

T

k3 k4 k5 k6

C

F

Digital modulation

MODULATIONS

o digital data is translated into an analog signal (baseband)o ASK, FSK, PSK - main focus in this chaptero differences in spectral efficiency, power efficiency, robustness

Analog modulation

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

17

o smaller antennas (e.g., l/4)o Frequency Division Multiplexingo medium characteristics

Basic schemes

o Amplitude Modulation (AM)o Frequency Modulation (FM)o Phase Modulation (PM)

Modulation and demodulation

analog

digitaldata

101101001

Digital modulation

digitalmodulation

analogdemodulation

radio

carrier

basebandsignal

analogbasebandsignal

analogmodulation

radio

carrier

synchronization

decision

digitaldata

101101001

Radio transmitter

Radio receiver

Modulation of digital signals known as Shift Keying.

Amplitude Shift Keying (ASK):

very simplelow bandwidth requirementsvery susceptible to interference

Frequency Shift Keying (FSK):

needs larger bandwidth

Phase Shift Keying (PSK):

18

more complexrobust against interference

1

1

1

Advanced Frequency Shift Keying

0

0

0

1

1

1

t

t

t

ASK

FSK

PSK

bandwidth needed for FSK depends on the distance between the carrier frequenciesspecial pre-computation avoids sudden phase shifts è MSK (Minimum Shift Keying)bit separated into even and odd bits, the duration of each bit is doubleddepending on the bit values (even, odd) the higher or lower frequency, original or inverted is chosenthe frequency of one carrier is twice the frequency of the othereven higher bandwidth efficiency using a Gaussian low-pass filterè GMSK (Gaussian MSK), used in GSM.

Advanced Phase Shift Keying

BPSK (Binary Phase Shift Keying):

bit value 0: sine wavebit value 1: inverted sine wavevery simple PSKlow spectral efficiencyrobust, used e.g. in satellite systems

19

QPSK (Quadrature Phase Shift Keying):

2 bits coded as one symbolsymbol determines shift of sine waveneeds less bandwidth compared to BPSKmore complex

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

BPSK (Binary Phase Shift Keying):

Q

I1 0

QPSK (Quadrature Phase Shift Keying):

Quadrature Amplitude Modulation

10

00

Q 11

I

01

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

20

Effects of spreading and interference

P

i)f

ii )

SPREAD SPECTRUM

P

f

user signalbroadband interferencenarrowband interference

iii )

P

f

sender

iv )

receiver

P

fv)

P

f

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 thesignal

o soft handoverDisadvantages

• precise power control necessary

21

user data

chippingsequence

X

spreadspectrumsignal

modulator

radiocarrier

transmitsignal

receivedsignal

demodulator

radiocarrier

transmitter

lowpassfilteredsignal

chippingsequence

X

correlator

products

integrator

sampledsums

decisiondata

receiver

FHSS (Frequency Hopping Spread Spectrum)

Discrete changes of carrier frequency

sequence of frequency changes determined via pseudo random number sequence

Two versionsFast Hopping:several frequencies per user bitSlow Hopping:several user bits per frequency

Advantagesfrequency selective fading and interference limited to short periodsimple implementationuses only small portion of spectrum at any time

Disadvantagesnot as robust as DSSSsimpler to detect

22

FHSS (Frequency Hopping Spread Spectrum)

tb

user data

f

f3

f2

f1

f

f3

f2

f1

0

td

1

td

tb: bit period

0 1

td: dwell time

1 t

t

t

slowhopping(3 bits/hop)

fasthopping(3 hops/bit)

Frequency Hopping Spread Spectrum

user datamodulator

transmitter

narrowbandsignal

modulator

frequencysynthesizer

spreadtransmitsignal

hoppingsequence

hopping

receivedsignal

demodulator

frequency

narrowbandsignal

demodulatordata

23

sequence synthesizerreceiver

Medium Access Control (MAC)

MAC

MAC protocol which were developed for nodes at short distance did not show good performance fornodes 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 wereavailable to them etc.

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

2. Sampling the water level of dam.These applications do not require frequent human intervention and are required to run for a longerduration.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 savingpower 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 time2. Time varying channel3. 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 ->“Impossibleto 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 ofcollision -> 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 dimensionsthan the wavelength of the radio wave e.g. reflection occurs from the surface of the earth and frombuildings and walls

24

• Diffraction – occurs when the radio path between the transmitter and the receiver is obstructed by asurface with sharp edges

• Scattering – occurs when the medium through which the wave travels consists of objects withThe 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 thetransmission (Very likely) for wire line networks the bit error rate (BER) is the probability of packet error issmall .For wire line networks the errors are due to random For wireless networks the BER is as high.For wirelessnetworks the errors are due to node being in fade as a result errors occur in a long burst. Packet loss due to bursterrors - 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 simultaneoustransmissions

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 cannotdetect 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’sreceived signal strength drops below a certain threshold the node is said to be in fade .Handshaking is widely usedstrategy to ensure the link quality is good enough for data communication. A successful handshake between asender and a receiver (small message) indicates a good communication link.

25

In theory C can therefore have a parallel transmission with any node that cannot hear the transmission fromB, i.e. out of range of B. But C will not transmit to any node because its an exposed node. Exposed nodeswaste bandwidth.

Capture

Capture is said to occur when a receiver can cleanly receive a transmission from one of two simultaneoustransmissions both within its range Assume node A and D transmit simultaneously to B. The signal strengthreceived from D is much higher than that from A, and D’s transmission can be decoded without errors in presenceof transmissions from A.D has captured A. Capture is unfair because it gives preference to nodes that are closer tothe 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 stationscommunicate only via the base station

Advantages of cell structures:

higher capacity, higher number of usersless transmission power neededmore robust, decentralizedbase station deals with interference, transmission area etc. locally

Problems:

fixed network needed for the base stationshandover (changing from one cell to another) necessaryinterference 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:

f4

f3

f5

f1

f2

f3

f6

f7

f2

f4

f5

f1

certain frequencies are assigned to a certain cellproblem: different traffic load in different cells

Dynamic frequency assignment:

base station chooses frequencies depending on the frequencies already used in neighbor cellsmore capacity in cells with more trafficassignment can also be based on interference measurements

f3

f1

f2

f3

f2

f3

f1

f3

f1

f2

f3

f2

f3

f1

f3

f1

f2

f3

f1

g1

f2

f3

g2

g3

h1

h2

h3

f1

g1

f2

f3

g2

g3

h1

h2

h3

f1

g1

f2

f3

g2

g3

3 cell cluster

Cell : Why Hexagon?

3 cell cluster with 3 sector antennas

• 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 onaccount of co channel interference uneconomical deployment of equipment, requiring relocation fromone cell site to another

YCS012 -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

System Architecture

Mobile Stations(MS)

Mobile Station (MS)

Base TransceiverStation (BTS)

BaseTransceiver

(BTS)

Um interface

BaseTransceiver

(BTS)

Base

Transceiver(BTS)

Base

Station(BSC)

Abis interface

Base Station(BS)

Base

Station(BSC)

Abis interface

Base Station(BS)

A interface

VLR

Mobile

gCentre)

CCITTSignalling

System No. 7(SS7)

interface

HLR

GMSC

PSTN

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 ahand-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 andconsist 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)

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 allowingoperation 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 ruggednesso reliabilityo portabilityo 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 ControllersMobile Switching CentersGSM-networksOther external networks

• Heart of the network• Three main jobs:

1) Connects calls from sender to receiver2) Collects details of the calls made and received3) Supervises operation of the rest of the network components

Home Location Registers (HLR)

- contains administrative information of each subscriber- Current location of the mobile

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 MobileEquipment 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• 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

7

History of satellite communication

SATELLITE NETWORKS

1945 Arthur C. Clarke publishes an essay about „ExtraTerrestrial Relays“1957 first satellite SPUTNIK1960 first reflecting communication satellite ECHO1963 first geostationary satellite SYNCOM1965 first commercial geostationary satellite Satellit „Early Bird“(INTELSAT I): 240 duplex telephone channels or 1 TVchannel, 1.5 years lifetime1976 three MARISAT satellites for maritime communication1982 first mobile satellite telephone system INMARSAT-A1988 first satellite system for mobile phones and datacommunication INMARSAT-C1993 first digital satellite telephone system1998 global satellite systems for small mobile phones

Applications

Traditionallyweather satellitesradio and TV broadcast satellitesmilitary satellitessatellites for navigation and localization (e.g., GPS)

Telecommunicationglobal telephone connectionsbackbone for global networksconnections for communication in remote places or underdeveloped areasglobal mobile communication

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

Classical satellite systems

Basics

Satellites in circular orbitsattractive force Fg = m g (R/r)²centrifugal force Fc = m r ω²m: mass of the satelliteR: radius of the earth (R = 6370 km)r: distance to the center of the earthg: acceleration of gravity (g = 9.81 m/s²)ω: angular velocity (ω = 2 π f, f: rotation frequency)

Stable orbitFg = Fc

Basics

o Elliptical or circular orbitso Complete rotation time depends on distance satellite-eartho Inclination: angle between orbit and equatoro Elevation: angle between satellite and horizono LOS (Line of Sight) to the satellite necessary for connection

1. High elevation needed, less absorption due to e.g. buildingso Uplink: connection base station - satelliteo Downlink: connection satellite - base stationo Typically separated frequencies for uplink and downlink

1. Transponder used for sending/receiving and shifting of frequencies2. Transparent transponder: only shift of frequencies3. Regenerative transponder: additionally signal regeneration

IElevation

Link budget of satellites

Parameters like attenuation or received power determined by four parameters:Sending powerGain of sending antennaDistance between sender and receiverGain of receiving antenna ProblemsVarying strength of received signal due to multipath propagationInterruptions due to shadowing of signal (no LOS) possible solutionsLink Margin to eliminate variations in signal strengthSatellite diversity (usage of several visible satellites at the same time) helps to use less sending power

L: Lossf: carrier frequencyr: distancec: 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 surfaceLEO (Low Earth Orbit): ca. 500 - 1500 kmMEO (Medium Earth Orbit) or ICO (Intermediate Circular Orbit):

ca. 6000 - 20000 kmHEO (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 rotationFix antenna positions, no adjusting necessarySatellites typically have a large footprint (up to 34% of earth surface!), therefore difficult to reuse frequenciesBad elevations in areas with latitude above 60° due to fixed position above the equatorHigh transmit power neededHigh 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 TVtransmission

LEO systems

Orbit ca. 500 - 1500 km above earth surfaceVisibility of a satellite ca. 10 - 40 minutes

Global radio coverage possibleLatency comparable with terrestrial long distanceConnections, ca. 5 - 10 msSmaller footprints, better frequency reuseBut now handover necessary from one satellite to anotherMany satellites necessary for global coverageMore complex systems due to moving satellites

Examples:Iridium (start 1998, 66 satellites)Global star (start 1999, 48 satellites)

MEO systems

Orbit ca. 5000 - 12000 km above earth surfaceComparison with LEO systems:Slower moving satellitesLess satellites neededSimpler system designFor many connections no hand-over needed

Higher latency, ca. 70 - 80 msHigher sending power neededSpecial antennas for small footprints neededExample:ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000

Routing

One solution: inter satellite links (ISL)Reduced number of gateways neededForward connections or data packets within the satellite network as long as possibleOnly one uplink and one downlink per direction needed for the connection of two mobile phonesProblems:More complex focusing of antennas between satellitesHigh system complexity due to moving routersHigher fuel consumptionThus shorter lifetimeIridium and Teledesic planned with ISLOther systems use gateways and additionally terrestrial networks

Localization of mobile stations

Mechanisms similar to GSMGateways maintain registers with user dataHLR (Home Location Register): static user dataVLR (Visitor Location Register): (last known) location of the mobile station

SUMR (Satellite User Mapping Register):Satellite assigned to a mobile stationPositions of all satellites

Registration of mobile stationsLocalization of the mobile station via the satellite’s positionRequesting user data from HLRUpdating VLR and SUMR

Calling a mobile stationLocalization using HLR/VLR similar to GSMConnection setup using the appropriate satellite

Handover in satellite systems

Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networkscaused by the movement of the satellitesIntra satellite handover

Handover from one spot beam to anotherMobile station still in the footprint of the satellite, but in another cell

Inter satellite handoverHandover from one satellite to another satelliteMobile station leaves the footprint of one satellite

Gateway handoverHandover from one gateway to another

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

Inter system handoverHandover from the satellite network to a terrestrial cellular networkMobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.

Overview of LEO/MEO systems

YCS012 -MOBILE COMPUTING

UNIT III

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 areao Ad-hoc networks without previous planning possibleo (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 useo no special permissions or licenses needed to use the LANo robust transmission technologyo simplified spontaneous cooperation at meetingso easy to use for everyone, simple managemento protection of investment in wired networkso 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

• Infrared– uses IR diodes, diffuse light,

multiple reflections (walls,furniture etc.)

• Advantages– simple, cheap, available in

many mobile devices– no licenses needed– simple shielding possible

• Disadvantages– interference by sunlight,

heat sources etc.– many things shield or

absorb IR light– low bandwidth

• Example– IrDA (Infrared Data

Association) interfaceavailable everywhere

Comparison: infrastructure vs. ad-hoc networks

• Radio– typically using the license

free ISM band at 2.4 GHz• Advantages

– experience from wirelessWAN and mobile phonescan be used

– coverage of larger areaspossible (radio canpenetrate walls, furnitureetc.)

• Disadvantages– very limited license free

frequency bands– shielding more difficult,

interference with otherelectrical devices

• Example– WaveLAN , HIPERLAN,

Bluetooth

infrastructurenetwork

AP

ad-hoc network

AP

wired network

AP: Access Point

AP

IEEE 802.11 - ARCHITECTURE – SERVICES - ARCHITECTURE – SERVICES – MAC – PHYSICAL LAYER – IEEE802.11A - 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 Pointo station integrated into the wireless LAN and the distribution system

Portalo bridge to other (wired) networks

Distribution Systemo interconnection network to form one logical network (EES: Extended Service Set) based

on several BSS

STA1

802.11 LAN

BSS1

AccessPoint

802. x LAN

Portal

ESS

STA2

Distribution System

AccessPoint

BSS2

802.11 LAN STA3

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

802.11 LAN

STA1

BSS1

STA2

BSS2

STA4

STA3

STA5

802.11 LAN

7.6.1

IEEE standard 802.11

Application

Transport

Application

Transport

Network

Data Link

Physical

802.11 - Layers and functions

MAC

Radio

Network

Data Link

Physical

Network

Data Link

Physical

Medium

Network

Data Link

Physical

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

802.11 - Layers

DLC

PHY

802.11 - Physical layer

LLC

MAC

PLCP

PMD

MAC Management

PHY Management

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/so 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

Infrared

Mbit/so 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

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

Priorities

DFWMAC-DCF CSMA/CA (mandatory)collision avoidance via randomized „back-off“ mechanismminimum distance between consecutive packetsACK packet for acknowledgements (not for broadcasts)

DFWMAC-DCF w/ RTS/CTS (optional)Distributed Foundation Wireless MACavoids hidden terminal problem

DFWMAC- PCF (optional)access point polls terminals according to a list

defined through different inter frame spacesno guaranteed, hard prioritiesSIFS (Short Inter Frame Spacing)

highest priority, for ACK, CTS, polling responsePIFS (PCF IFS)

medium priority, for time-bounded service using PCFDIFS (DCF, Distributed Coordination Function IFS)

lowest priority, for asynchronous data service802.11 - MAC layer

DIFS

medium busy

direct access if

DIFS

PIFS

SIFScontention next frame

t

MAC address format

medium is free DIFS

scenario to DS fromDS

address 1 address 2 address 3 address 4

8

ad-hoc networkinfrastructurenetwork, from APinfrastructurenetwork, to AP

0 0

1

0 1

0

DA DA

BSSID

SA BSSID

SA

BSSIDSA

DA

--

-

Vasantha Kumar .VRA Lecturer CSE

infrastructurenetwork, within DS

1 1 TA DA SA

DS: Distribution SystemAP: Access PointDA: Destination AddressSA: Source AddressBSSID: Basic Service Set IdentifierRA: Receiver AddressTA: Transmitter Address

MAC management

Synchronizationtry to find a LAN, try to stay within a LANtimer etc.

Power managementsleep-mode without missing a messageperiodic sleep, frame buffering, traffic measurements

Association/Reassociationintegration into a LANroaming, i.e. change networks by changing access points scanning, i.e. active search for a network

MIB - Management Information Basemanaging, read, write

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

higher layers

medium accesscontrol layer

channel accesscontrol layer

physical layer

HIPERLAN layers

network layer

data link layer

physical layer

OSI layers

logical linkcontrol layer

medium accesscontrol layer

physical layer

IEEE 802.x layers

7.31.1

Original HIPERLAN protocol family

HIPERLAN 1 HIPERLAN 2HIPERLAN 3 HIPERLAN 4Application wireless LAN access to ATM wireless localpoint-to-point

Frequency

fixed networks

5.1-5.3GHz

loop wireless ATMconnections17.2-17.3GHz

Topology decentralized ad cellular, point-to- point-to-point

Antennahoc/infrastructure centralized

omni-directionalmultipoint

directionalRange 50 m 50-100 m 5000 m 150 m QoS statistical ATM traffic classes (VBR, CBR, ABR, UBR)MobilityInterface

<10m/sconventional LAN

stationaryATM networks

Data ratePower conservation

23.5 Mbit/s yes

>20 Mbit/s 155 Mbit/snot necessary

HIPERLAN 1 - Characteristics

Data transmissionpoint-to-point, point-to-multipoint, connectionless23.5 Mbit/s, 1 W power, 2383 byte max. packet size

Servicesasynchronous and time-bounded services with hierarchical prioritiescompatible with ISO MAC

Topologyinfrastructure or ad-hoc networkstransmission range can be larger then coverage of a single node („forwarding“ integrated in mobileterminals)

Further mechanismspower saving, encryption, checksums

Services and protocols

CAC servicedefinition of communication services over a shared mediumspecification of access prioritiesabstraction of media characteristics

MAC protocolMAC service, compatible with ISO MAC and ISO MAC bridgesuses HIPERLAN CAC

CAC protocolprovides a CAC service, uses the PHY layer, specifies hierarchical access mechanisms for one orseveral channels

Physical protocolsend and receive mechanisms, synchronization, FEC, modulation, signal strength

HIPERLAN 1 - Physical layer

Scopemodulation, demodulation, bit and frame synchronizationforward error correction mechanismsmeasurements of signal strengthchannel sensing

Channels3 mandatory and 2 optional channels (with their carrier frequencies)mandatory

channel 0: 5.1764680 GHzchannel 1: 5.1999974 GHzchannel 2: 5.2235268 GHz

optional (not allowed in all countries)channel 3: 5.2470562 GHzchannel 4: 5.2705856 GHz

BLUETOOTH

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

Scenariosconnection of peripheral devices

loudspeaker, joystick, headsetsupport of ad-hoc networking

small devices, low-costbridging of networks

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

Simple, cheap, replacement of IrDA, low range, lower data rates2.4 GHz, FHSS, TDD, CDMA

Bluetooth MAC layer

• Synchronous Connection -Oriented link (SCO)– symmetrical, circuit switched, point -to -point

• Asynchronous Connectionless Link (ACL)– packet switched, point

• Access code-to -multipoint, master polls

– synchronization, derived from master, unique per channel• Packet header

– 1/3 -FEC, MAC address (1 master, 7 slaves), link type,alternating bit ARQ/SEQ, checksum

72 54 0-2745 bits

access code packet header

3 4 1 1

payload

1 8 bits

MOBILE NETWORK LAYER

YCS012 -MOBILE COMPUTING

UNIT IV

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 layerNetwork LayerTransport Layer

What does IP domoving packets from source to destinationNo ’end-to-end’ guarantees

IP addressesNetwork-prefixHost portion

IP RoutingPacket HeaderNetwork-prefixEvery 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 receivepackets at the new link; andIf a node moves from one link to another without chnging its IP address, it will be unable to receivepackets at the new link; and

Mobile IP Overview

Solution for Internet

Scalable, robust, secure, maintain communicationUse their permanent IP address

Routing protocolRoute packets to nodes that could potentially change location very rapidly

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

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 COAver. IHL TOS length

IP identificationTTL IP-in-IP

flags fragment offsetIP checksum

ver. IHL

IP address of HACare-of address COATOS

length

IP identificationTTL lay. 4 prot.

flags fragment offsetIP checksum

Mobile IP and IPv6

IP address of CNIP address of MN

TCP/UDP/ ... payload

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 addressauto configuration

• No need for a separate FA, all routers perform router advertisement which can be used instead ofthe special agent advertisement;

• Addresses are always co-located

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

Motivation for Mobile IP

Routing

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, securityproblems

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 lowbandwidth radio link)

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

• Internet

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

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

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 HOST CONFIGURATION PROTOCOL

Dynamic Host Configuration Protocol (DHCP) is a network protocol for automatically assigning TCP/IPinformation to client machines. Each DHCP client connects to the centrally-located DHCP server whichreturns 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 clientsystem, 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 anadministrator wants to change the IP addresses of a large number of systems. Instead of reconfiguring allthe systems, he can just edit one DHCP configuration file on the server for the new set of IP addresses. Ifthe DNS servers for an organization changes, the changes are made on the DHCP server, not on the DHCPclients. 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 fromoffice to office without being reconfigured as long as each office has a DHCP server that allows it toconnect to the network.

Configuration File

The first step in configuring a DHCP server is to create the configuration file that stores the networkinformation for the clients. Global options can be declared for all clients, while other options can bedeclared 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 interimDHCP-DNS interaction draft update mode. If and when these two are accepted as part of the InternetEngineering Task Force (IETF) standards process, there will be a third mode — the standard DNS updatemethod. The DHCP server must be configured to use one of the two current schemes. Version 3.0b2pl11and 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 forthe 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 configureDHCP options; whereas, parameters configure values that are not optional or control how the DHCPserver behaves.

8

In Example the routers, subnet-mask, domain-name, domain-name-servers, and time-offset options are usedfor any host statements declared below it.Additionally, a subnet can be declared, a subnet declaration must be included for every subnet in thenetwork. 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;

}

DSR

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 (reactivealgorithm)

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

(path was collected in the packet) if the packet has already been received earlier (identified via 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 andmobile 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, pushtechnologies etc.

• many hyperlinks, automatic loading and reloading, redirecting

• a single click might have big consequences!

YCS012 -MOBILE COMPUTING

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 fillup.

Full Duplex

• TCP provides transfer in both directions.

• To the application program these appear as 2 unrelated data streams, although TCP can piggyback controland 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

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

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 benumber 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 detailsasynchronously.

• 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 ina 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.

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

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

I

Internet Model

WAP Architecture

HTMLHTTP

TLS/SSLTCP/IP

Client

WML

WML-Script

WTAI

Etc.

WSP/WTP

WAPGateway

WML Encoder

WMLScriptCompiler

Protocol Adapters

HTTP

WebServer

CGIScript

setc.

Content

WMLDecks

withWML-

WAP Application Server

Client

Script

WML WML Encoder ApplicationWML -Script

WTAI

Etc.

WSP/WTP WMLScriptCompiler

Protocol Adapters

Logic

Content

WAP Application Server

WAP: Network Elements

fixed network wireless network

WM

L D

ecks

wit

h W

ML

-Scr

ipt

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

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• 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)

WAE: Logical Model

Origin Servers Gateway Client

webserver

other content

server

WML: Wireless Markup Language

Tag-based browsing language:

responsewithcontent

pushcontent

request

Method proxy

Push proxy

encoders&

decoders

encodedresponsewithcontent

encodedpushcontent

encodedrequest

WTAuser agent

WMLuser agent

otherWAE

user agents

– Screen management (text, images)– Data input (text, selection lists, etc.)– Hyperlinks & navigation support

Takes into account limited display, navigation capabilities of devicesXML-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 mgmtThe basic unit is a card. Cards are grouped together into Decks Document ~ Deck (unit of transfer)All decks must contain

– Document prologueXML & document type declaration

– <WML> elementMust 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: <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 functionsURL - URL processingBrowser - WML browser interfaceDialog - simple user interfaceFloat - 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

• 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 quotesWireless 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 modelPush initiator is the clientPush proxy is the serverInitiator uses HTTP POST to send push message to proxyInitiator sends control information as an XML document, and content for mobile (as WML)Proxy sends XML entity in response indicating submission statusInitiator 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– 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):– 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-I WIRELESS COMMUNICATION FUNDAMENTALS

1. What is mobile computing?

Mobile computing is a technology that allows transmission of data, via a computer, without having to be connected to a fixed physical link.

2. What are two different kinds of mobility?

User Mobility: It refers to a user who has access to the same or similar telecommunication services at different places.

Device Portability: many mechanisms in the network and inside the device have to make sure that communication is still possible while the device is moving.

3. Find out the characteristics while device can thus exhibit during communication.

Fixed and Wired Mobile and Wired Fixed and Wireless Mobile and Wireless

4. What are applications of Mobile Computing?

Vehicles Emergencies Business Replacement of wired networks Infotainment Location dependent services

Follow-on services Location aware services Privacy

MOBILE COMPUTING

Information services Support services

Mobile and wireless devices Sensor Embedded controllers Pager Mobile phones Personal digital assistant Pocket computer Notebook/laptop

5. What are the obstacles in mobile communications?

Interference Regulations and spectrum Low Bandwidth High delays, large delay variation Lower security, simpler to attack Shared Medium Adhoc-networks.

6. What is TETRA?

TETRA (Terrestrial Trunked Radio) systems use different radio carrier frequencies, but they assign a specific carrier frequency for a short period of time according to demand. TETRA’s are highly reliable and extremely cheap.

7. Which elements of the network perform the data transfer? Physical medium

8. Compare the different types of transmission errors that can occur in wireless and wired networks.

Types of Error: Data loss Noise Low power

9. Define Signal. A signal is defined as any physical quantity carrying information that varies

with time. The value of signal may be real or complex. The types of signal are continuous signal and discrete time signal.

10. Define antenna. An antenna or aerial is one or more electrical conductors of a specific length

that radiate radio waves generated by a transmitter or that collect radio waves at the receiver.

MOBILE COMPUTING

11. State the relation between wavelength and frequency.

Wavelength is the length or distance of one cycle of an ac wave. It is also the distance that an ac wave travels in the time required for one cycle of that signal. Wavelength is expressed as the ratio of the speed of light to the frequency of the signal

12. What are the main problems of signal propagation?

Power additionally influenced by fading (frequency dependent) shadowing Reflection at large obstacles Refraction depending on the density of a medium scattering at small obstacles Diffraction at edges

13. How a receiver adopts for Multi-path propagation effects during wireless

reception?

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.

14. What is multipath propagation?

Multipath propagation is the direct from a sender to a receiver the propagation effects mentioned in the previous section lead to one of the most severe radio channel impairments.

15. What are the types of Frequency Modulation?

Based on the modulation index FM can be divided into types. They are Narrow band FM and Wide band FM. If the modulation index is greater than one then it is wide band FM and if the modulation index is less than one then it is Narrow band FM.

16. What is the basic difference between an AM signal and a narrowband FM signal?

In the case of sinusoidal modulation, the basic difference between an AM signal and a narrowband FM signal is that the algebraic sign of the lower side frequency in the narrow band FM is reversed.

17. How will you generate message from frequency-modulated signals?

First the frequency-modulated signals are converted into corresponding amplitude-modulated signal using frequency dependent circuits.Then the original signal is recovered from this AM signal.

MOBILE COMPUTING

18. What is called multipath Interference?

The interference caused by the interfacing of the signal form the indirect path with the signal of direct path is called multipath interference.

19. Define reflection loss

Reflection loss is defined as the number of nippers or decibels by which the current in the load under image matched conditions would exceed the current actually flowing in the load

20. Define multiplexing.

Multiplexing is defined as the process of transmitting several message signals simultaneously over a single channel.

21. List out the various Multiplexing Schemes?

Space division multiplexing Frequency division multiplexing Time division multiplexing Code division multiplexing

22. Give the use of SDMA./ 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).

23. 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. Auto Correlation.

24. What the features are of Code Division multiple Accesses?

It does not require external synchronization networks. CDMA offers gradual degradation in performance when the no. of

users is increased But it is easy to add new user to the system. If offers an external interference rejection capability.

MOBILE COMPUTING

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

The guard space between a pair of users in CDMA systems is the orthogonality between their spreading codes. The lower the correlation between any pair of spreading codes is, the better is the user separation.

26. What is hopping sequence?

Transmitter and receiver stay on one of the channels like and TDM. The pattern of channel usage is called the hopping sequence,

27. What is the need for modulation? Needs for modulation:

Ease of transmission Multiplexing Reduced noise Narrow bandwidth Frequency assignment Reduce the equipments limitations.

28. Give the classification of modulation.

There are two types of modulation. They are Analog modulation Digital modulation

29. Give the classification of Digital modulation.

Amplitude shift keying Phase shift keying Frequency shift keying

30. Define demodulation.

Demodulation or detection is the process by which modulating voltage is recovered from the modulated signal. It is the reverse process of modulation.

31. Define stability. It is the ability of the receiver to deliver a constant amount of output for a

given a given period of time.

32. What are the 3 different basic schemes analog modulations?

1. Amplitude modulation 2. Frequency modulation 3. Phase modulation

MOBILE COMPUTING

33. Define frequency modulation.

Frequency modulation is defined as the process by which the frequency of the carrier wave is varied in accordance with the instantaneous amplitude of the modulating or message signal.

34. Define phase modulation.

Phase modulation is defined as the process of changing the phase of the carrier signal in accordance with the instantaneous amplitude of the message signal.

35. What is the advantage of a spread spectrum technique?

The main advantage of spread spectrum technique is its ability to reject interference whether it be the unintentional interference of another user simultaneously attempting to transmit through the channel (or) the intentional interference of a hostile transmitter to jam the transmission.

36. What is called frequency hop spread spectrum?

In frequency hop spread spectrum, the frequency of the carrier hops randomly from one frequency to another frequency.

37. What is the function of Medium Access Control Layer?

The functions of Medium Access Control Layer are responsible for establishes, maintains, and releases channels for higher layers by activating and deactivating physical channels.

38. 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

39. 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.

40. 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 probability1-p, i.e. access is slotted in addition.

41. What is FDD?

MOBILE COMPUTING

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)

42. What is dwell time?

The time spend on a channel with a certain frequency is called the dwell time

43. What is fast frequency hopping?

If the hop rate is an integer multiple of symbol rate (multiple hops per symbol) then it is called fast frequency hopping.

44. What is slow frequency hopping?

If the symbol rate of MFSK is an integer multiple of hop rate (multiple symbols per hop) then it is called slow frequency hopping.

45. What is a burst error?

A burst error is when two or more consecutive bits within a given data string are in error. These errors can affect one or more characters within a message.

46. What are the 2 sub layers in DLC?

o Logical Link Control(LLC) o Media Access Control(MAC)

47. Define traffic multiframe and control multiframe?

1. The periodic pattern of 26 slots occurs in all TDMA frames with a TCH.

2. The combination of these frames is called traffic multiframe 3. TDMA frames containing data for the other logical channels are

combined to a control multiframe.

48. Explain about transparent mode?

The transparent mode transfer simply forwards MAC data without any further processing. The system then has to rely on the FEC which is always used in the radio layer.

49. List out the advantage of cellular wireless networks.

Higher capacity, higher number of users Less transmission power needed More robust, decentralized Base station deals with interference, transmission area etc.

MOBILE COMPUTING

UNIT II TELECOMMUNICATION NETWORKS

1. What are the disadvantages of cellular systems?

The advantages of cellular systems are,

Infrastructure needed Hand over needed Frequency planning

2. What are the basic groups of logical channels?

GSM specifies 2 basic groups of logical channels,

Traffic channels Control channels

3. What are the categories of Mobile services? Bearer services Tele services Supplementary services

4. What are subsystems in GSM system? Radio subsystem (RSS) Network & Switching subsystem (NSS) Operation subsystem (OSS)

5. What are the control channel groups in GSM?

The control channel groups in GSM are:

Broadcast control channel (BCCH) Common control channel (CCCH) Dedicated control channel (DCCH)

6. 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

7. Give the information’s in SIM?

card type, serial no, list of subscribed services Personal Identity Number(PIN) Pin Unlocking Key(PUK) An Authentication Key(KI)

8. What is the frequency range of uplink and downlink in GSM network? The frequency range of uplink in GSM network is 890-960 MHz The frequency range of downlink in GSM network is 935-960 MHz

MOBILE COMPUTING

9. What are the security services offered by GSM? The security services offered by GSM are:

Access control and authentication. Confidentiality. Anonymity.

10. What are the control channel groups in GSM?

The control channel groups in GSM are: Broadcast control channel (BCCH). Common control channel (CCCH). Dedicated control channel (DCCH).

11. What is authentication centre (AuC)?

As the radio interface and mobile stations are particularly vulnerable a separate AuC has been defined to protect user identity and data transmission. The AuC contains the algorithms for authentication as well as the keys for encryption and generates the values needed for user authentication in the HLR. The AuC may, in fact, be situated in a special protected part of the HLR.

12. What is Network and Switching subsystem?

The heart of the GSM is formed by the Network and Switching System (NSS). NSS consists of the following switches and databases:

• Mobile Services switching Center (MSC) • Home Location register (HLR) • Visitor Location Register (VLR)

13. What are the services provided by supplementary services?

• User identification • Call redirection • Call forwarding • Closed user groups • Multiparty Communication

14. What are types of Handover?

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

15. What are the reasons for delays in GSM for packet data traffic?

Collisions only are possible in GSM with a connection establishment. A slotted ALOHA mechanism is used to get access to the control channel by which the base station is told about the connection establishment attempt. After connectionestablishment, a designated channel is installed for the transmission.

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16. If 8 speech channels are supported on a single radio channel, and if no guard band is assumed, what is the number of simultaneous users that can be accommodated in GSM?

1000 users.

17. What is meant by beacon? A beacon contains a timestamp and other management information used for

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

18. List out the numbers needed to locate an MS and to address the MS.

The numbers needed to locate an MS and to address the MS are:

Mobile station international ISDN number (MSISDN)

International mobile subscriber identity (IMSI)

Temporary mobile subscriber identity (TMSI) Mobile station roaming number (MSRN)

19. 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.

20. What is meant by GGSN?

GGSN is Gateway GPRS Support Node. It is the inter-working unit between the GPRS network and external packet data networks. The GGSN is connected to external networks via the Gi interface and transfers packets to the SGSN via an IP-based GPRS backbone network.

21. What is meant by SGSN?

SGSN is Serving GPRS Support Node. It supports the MS via the Gb

interface. The GSN is connected to a BSC via frame relay.

22. What is meant by BSSGP?

BSSGP is Base Station Subsystem GPRS Protocol. It is used to convey routing and QoS- related information between the BSS and SGSN.BSSGP does not perform error correction and works on top of a frame relay network.

23. Define the protocol architecture of DECT.

The protocol architecture of DECT consists of three layers. They are:

1. Physical Layer.

2. Medium Access Layer.

3. Data Link Control Layer.

4. Network Layer.

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24. What are the steps perform during the search for a cell after power on?

The steps perform during the search for a cell after power on is:

Primary Synchronization.

Secondary Synchronization.

Identification of the scrambling code.

25. What are the applications in satellites?

Weather forecasting satellites Radio & TV broadcast satellites Military satellites Satellites for navigation Mobile communication

26. Define the terms: (i). Earth Station,(ii). Uplink,(iii). Downlink. Earth Station:-The antenna systems on or near the earth are referred to as Earth Station. Uplink:-A transmission from an earth station to the satellite is referred to as Uplink. Downlink:-A transmission from the satellite to the earth station is referred to as Downlink.

27. What are the factors limited the number of sub channels provided within the satellite channel?

There are three factors limited the number of sub channels provided within the

satellite channel. They are:

Thermal Noise.

Inter modulation Noise.

Cross talk.

28. What is meant by GEO?

GEO means Geostationary or Geosynchronous earth orbit.GEO satellites have a distance of almost 36000 km to the earth. Examples are almost all TV and radio broadcast satellites, many weather satellites and satellites operating as backbone for the telephone network.

29. What is communication satellite?

Communications satellite is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits.

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30. What are the registers maintained by the gateway of satellite?

1. Home Location Register (HLR)

2. Visitor Location Register (VLR)

3. Satellite User Mapping Register (SUMR)

31. What are the advantages of LEO?

Data rate is 2400 bit/s Packet delay is relatively low Smaller footprints of LEO allows frequency reuse Provide high elevations

32. Define the inclination angle and perigee. The inclination angle is defined as the angle between the equatorial plane

and the lane described by the satellite orbit. An inclination angle of 0 degrees means that the satellite is exactly above the equator. If the satellite does not have a circular orbit, the closest point to the earth is called the perigee.

33. Define the elevation angle and footprint. The elevation angle is defined as the angle between the centre of satellite

beam and the plane tangential to the earth's surface. The foot-print can be defined as the area on earth where the signals of the satellite can be received.

34. What are the advantages of GEO?

Three GEO satellites are enough for a complete coverage of almost any spot on earth, senders and receivers can use fixed antennas positions, and no adjusting is needed. Therefore GEO’s are ideal for T.V and radio broadcasting

35. What is Handover?

The satellite is the base station in satellite communication systems and that it is moving. So, additional instance of handover are necessary due to the movement ofthe satellite

1. Intra Satellite handover: 2. Inter Satellite handover. 3. Gateway handover. 4. Inter System handover.

36. Advantages of MEO.

Using Orbits around 10,000Km, the system only requires a dozen satellites which is more than the GEO system, but much less than a LEO system. Furthermore these satellites move slower relative to the earth’s rotation allowing a simpler system design. Depending on the inclination a MEO can cover larger populations, thus requiring less handovers.

37. What is browsing channel allocation and fixed channel allocation?

Cells with more traffic are dynamically allotted more frequencies. This scheme is known as browsing channel allocation, while the first fixed scheme is called fixed channel allocation.

MOBILE COMPUTING

38. Write short notes on DAB.

MSC

FIC

DAB Frame Structure Components of DAB sender

Multimedia Object Transfer Protocol

39. What are the two basic transport mechanisms used by DAB?

The two basic transport mechanisms used by DAB are: 1. Main Service Channel (MSC). 2. Fast Information Channel (FIC).

40. 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.

41. 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.

42. 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……..

43. State the different types of transport modes and the channel used to carry packets in Digital Audio Broadcasting.

Two transport modes are possible in main service channel, namely, stream mode and packet mode.

Each frame has three parts, namely synchronization channel, fast information channel and main service channel.

44. What is FIC?

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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.

45. What is MSC?

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

46. What are the two transport modes defined for MSC?

The two transport modes defined for MSC are: o Stream Mode o Packet Mode.

47. 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)

48. What is EIT?

Event Information Table (EIT) contains status information about the current transmission and some additional information for set-top boxes. 49. 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)

50. What are the advantages of DVB?

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

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

Can be used in remote areas and developing countries where there is no high band width wired network.

51. What is EY-NMPA?

Elimination yield -Non Pre-emptive Multiple Access (EY-NMPA) is a

scheme which uses several phases to sense the medium. Access the medium

and for contention resolution. Priority schemes can also be included. This is actually

used in HIPERLAN1 specification.

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UNIT III WIRLESS LAN

1. What are the Advantages of wireless LAN?

Flexibility,

Planning,

Design,

Robustness,

Quality Service,

Cost,

Proprietary Solution,

Restriction, Safety and Security

2. What are the 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

3. Mention some of the disadvantages of WLANS?• Quality of service • Proprietary solutions. • Restrictions • Safety and Security

4. Mention the features of radio transmission?

• Cover large areas. • Can penetrate walls, furniture’s. • Does not need a LOS. • Higher transmission rates.

5. What are the disadvantages of radio transmission? • Shielding is not so simple. • Can interfere with other senders. • Limited ranges of license-free bands.

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6. Mention the features of infrared transmission? • Simple • Extremely cheap • Licenses are not needed • Electrical devices do not interfere

7. What are Advantages and Disadvantages of Infrared?

Advantages:

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

No licenses are needed for infrared technology and shielding is very simple. Electrical devices do not interfere with infrared transmission.

Disadvantages: i. Low bandwidth

ii. Quite easily shielded iii. Cannot Penetrate

8. What is the difference between infrastructure and ad-hoc networks?

Infrastructure-based wireless networks: Communication takes place only between the wireless nodes and the access

point, but not directly between the wireless nodes.

Ad-hoc wireless networks: Communication takes place directly with other nodes, so no access point

Controlling medium access is necessary.

9. Define frequency hopping spread spectrum? FHSS allows for the coexistence of multiple networks in the same area by

separating different networks using different hopping sequences.

10. Define random back off time? If the medium is busy, nodes have to wait for the duration of DIFS, entering a

contention phase afterwards. Each node now chooses a random back off time within a contention window and delays medium access for this random amount of time.

11. What is the primary goal of IEEE 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.

12. Is IEEE 802.11 and Wi-Fi same/ State the purpose of Wi-Fi.

Ans: No It is wireless internet. Your laptop has an internal wireless card so you can

connect to wireless routers. If you goto a hotel that advertises free wireless internet, you should be able to connect to it. You don't have to have an Ethernet cable to connect to the web at home either.

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13. Why the PHY layer of IEEE 802.11 is subdivided? What about HiperLAN2 and Bluetooth?

o PLCP Physical Layer Convergence Protocol o Clear channel assessment signal (carrier sense) o PMD Physical Medium Dependent o Modulation, coding o PHY Management channel selection, o MIB Station Management coordination of all management functions

14. What are the various versions of a physical layer defined in IEEE 802.11 standards?

IEEE 802.11-83.5 MHz IEEE 802.11a -300 MHz IEEE 802.11b. 83.5 MHz IEEE 802.11g - 83.5 MHz

15. What are the system integration functions of MAC management?

Synchronization Power management Roaming Management information base (MIB)

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

The main problem for WATM during the hand over 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

Hand over segment is affected by the hand over and is located completely

within a hand over domain.

18. 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.

19. What is SCO? SCO-stands for Synchronous Connection Oriented Link Standard telephone

(voice) connection require symmetrical, circuit-switched, point-to-point connections. For this type of link, the master reserves two consecutive slots at fixed intervals.

20. 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.

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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.

21. What do you meant by roaming?

Moving between access points 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.

22. 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.

23. 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

24. What are the examples for service scenarios identified in WATM?

Office environments Universities, schools, training, centers Industry Hospitals Home Networked vehicles

25. 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.

26. What are the different network types of BRAN?

Hyperlan1 Hyperlan2 Hyper access Hyperlink

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27. 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.

28. 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.

29. What is anchor point?

The Anchor point is the boundary between a handover segment and a fixed segment.

30. What are different types of handover?

Hard handover Terminal initiated Network initiated Network initiated, terminal assisted Network controlled Backward handover Forward handover

31. 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 points 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.

32. What are the three Low Power States provided by Bluetooth?

PARK state HOLD state SNIFF state

33. Mention the elements of Bluetooth core protocols?

• Radio • Baseband • Link manager protocol • Logical link control and adaptation protocol • Service discovery protocol

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34. What is the purpose of sniff state?

The sniff state has the highest power consumption. The device listens to the piconet at a reduced rate.

35. What is the use of hold state? The device does not release its AMA but stops ACL transmission. A slave

may still exchange SCO packets.

36. What is the purpose of park state? In this state the device has the lowest duty cycle and the lowest power

consumption. The device releases its AMA and receives a parked member address. The device is still a member of the piconet, but gives room for another device to become active.

37. How does registration on layer 3 of a mobile node work?

In the real system, a mobile node can connect to the network by using multiple interfaces with different access technologies such as Wi-Fi, CDMA. At the same time it can perform multiple connections for multiple services such as video, voice, or just chatting.

38. What are the advantages and problems of forwarding mechanisms in Bluetooth networks regarding security and power saving?

Advantage: Bluetooth network enables setting up of the network without much preparation. It sets itself automatically.

Problems: Security and power are major constraints. Security may be compromised and power may be spent on traffic not meant for a particular device.

39. Why Bluetooth specification comprises so many protocols and components?

The Bluetooth protocol stack, in common with all such standards, is specified as several separate layers

MOBILE COMPUTING

UNIT IV MOBILE NETWORK LAYER

1. What are the requirements of mobile IP?

• Compatibility

• Transparency

• Scalability and efficiency

• Security

2. Mention the different entities in a mobile IP.

• Mobile Node

• Correspondent Node

• Home Network

• Foreign Network

• Foreign Agent

• Home Agent

• Care-Of address

Foreign agent COA Co-located COA

3. Define 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.

4. Explain Cellular IP.

CellularIP provides local handovers without renewed registration by installing a single cellularIP gateway for each domain, which acts to the outside world as a foreign agent.

5. What do you mean by mobility binding?

The Mobile Node sends its registration request to the Home Agent. The HA now sets up a mobility binding containing the mobile node’s home IP address and the current COA.

6. 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. DHCP is a good candidate for supporting the acquisition of Care Of Addresses.

7. Define a tunnel.

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

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

the tunnel unchanged.

8. What is encapsulation?

Encapsulation is the mechanism of taking a packet consisting of packet header and data putting it into the data part of a new packet.

9. What is decapsulation?

The reverse operation, taking a packet out of the data part of another packet, is called decapsulation.

10. Define an outer header.

The HA takes the original packet with the MN as destination, puts it into the data part of a new packet and sets the new IP header in such a way that the packet is routed to the COA. The new header is called the outer header.

11. Define an inner header.

There is an inner header which can be identical to the original header as this case for IP-in-IP encapsulation, or the inner header can be computed during encapsulation.

12. What is meant by generic routing encapsulation?

Generic routing encapsulation allows the encapsulation of packets of one protocol suite into the payload portion of a packet of another protocol suite.

13. Why is need of routing?

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

14. What is the use of network address translation?

The network address translation is used by many companies to hide internal resources and to use only some globally available addresses.

15. Define triangular routing.

The inefficient behavior of a non-optimized mobile IP is called triangular routing. The triangle is made up of three segments, CN to HA, HA to COA\MN, and MN back to CN.

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16. What is meant by a binding cache?

One way to optimize the route is to inform the CN of the current location by caching it in a binding cache which is a part of the local routing table for the CN.

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

18. What is known as Binding update?

This message sent by the HA to CNs reveals the current location of the MN.

The message contains the fixed IP address of the MN and the COA. The binding

update can request an acknowledgement.

19. Explain binding acknowledgement.

If requested, a node returns this acknowledgement receiving a binding update message.

20. Define binding warning.

If a node decapsulates a packet for a MN, but it is not the current FA for this MN, this node sends a binding warning. The warning contains MN’s home address and a target node address.

21. What are the advantages of cellular IP?

Manageability:

Cellular IP is mostly self-configuring, and integration of the CIPGW

into a firewall would facilitate administration of mobility-related

functionality.

Efficiency

Transparency Security

22. What is known as mobility anchor point?

HMIPv6 provides micro-mobility support by installing a mobility anchor point, which is responsible for a certain domain and acts as a local HA within this domain for visiting MNs.

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23. Explain destination sequence distance vector routing.

Destination sequence distance vector routing is an enhancement to distance vector routing for ad-hoc networks and is used as routing information protocol in wired networks.

24. What are the two things added to the distance vector algorithm?

• Sequence Numbers • Damping

25. How the dynamic source routing does divide the task of routing into two separate problems?

1. Route discovery 2. Route Maintenance

26. How can DHCP be used for mobility and support of mobile IP?

Normally, a mobile node uses a care-of-address. In some cases, the mobile node may have to act as its own foreign agent by using co-located care of address. The means by which a mobile node acquires a co-located address is beyond the scope of mobile IP. One means is to dynamically acquire temporary IP address an the move using services such as DHCP.

27. List out the some of the popular Routing protocols.

DSDV(Destination Sequence Distance Vector) DSR(Dynamic Source Routing) AODV(Ad-Hoc On Demand Vector Routing)

28. 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.

29. Specify the field of minimal encapsulation method in mobile network layer.

o Minimal encapsulation doing,

o Avoids repetition of identical fields e.g. TTL, IHL, version, TOS

o Only applicable for unfragmented packets, no space left for fragment

identification

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30. What do you meant by roaming?

Moving between access points is called roaming. Even wireless networks may require more than one access point to coverall rooms. In order to provide uninterrupted service, we require roaming when the user moves from one access point to another.

31. 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.

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UNIT V TRANSPORT AND APPLICATION LAYERS

1. What is slow start?

TCP’s reaction to a missing acknowledgement is necessary to get rid of congestion quickly. The behavior TCP shows after the detection of congestion is called slow start.

2. What is the use of congestion threshold?

The exponential growth of the congestion window in the slow start mechanism is dangerous as it doubles the congestion window at each step. So a congestion threshold is set at which the exponential growth stops.

3. What led to the development of Indirect TCP?

• TCP performs poorly together with wireless links • TCP within the fixed network cannot be changed.

This led to the development of I-TCP which segments a TCP connection into a fixed part and a wireless part.

4. What is the goal of M-TCP?

The goal of M-TCP is to prevent the sender window from shrinking if bit errors or disconnection but not congestion cause current problems. It wants • To provide overall throughput

• To lower the delay • To maintain end-to-end semantics of TCP • To provide a more efficient handover.

5. What do you mean by persistent mode?

Persistent mode is the state of the sender will not change no matter how long the receiver is disconnected. This means that the sender will not try to retransmit the data.

6. What are the characteristics of 2.5G/3.5G wireless networks?

• Data rates • Latency • Jitter • Packet loss

7. What are the configuration parameters to adapt TCP to wireless environments?

• Large Windows • Limited Transmit • Large MTU

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• Selective Acknowledgement • Explicit Congestion Notification • Timestamp • No header compression

8. State the requirements of WAP.

• Interoperable • Scalable • Efficient • Reliable • Secure

9. Name the layers of WAP.

• Transport layer • Security layer • Transaction layer • Session layer • Application layer

10. Name some ICMP messages.

• Destination unreachable • Parameter problem • Message too big • Reassembly failure • Echo request/reply

11. What is WTP? What are its classes?

WTP stands for Wireless Transaction Protocol. It has been designed to run on very thin clients such as mobile phones. It has three classes.

• Class 0: provides unreliable message transfer without any result message. • Class 1: provides reliable message transfer without exactly one reliable result message. • Class 2: provides reliable message transfer with exactly one reliable result message.

12. What is WSP?

The Wireless Session Protocol has been designed to operate on top of the

datagram service WDP or the transaction service WTP. It provides a shared state between a client and a server to optimize content transfer.

13. Name some features of WSP adapted to web browsing.

• HTTP/1.1 functionality • Exchange of session headers • Push and pull data transfer • Asynchronous request

14. What is WML?

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The Wireless Markup Language is based on the standard HTML known from the www and on HDML. WML is specified as an XML document type.

15. What are the features of WML? • Text and Images • User interaction • Navigation • Context Management

16. What are the advantages of WML Script over WML?

WML Script offers several capabilities not supported by WML: • Validity check of user input • Access to device facilities • Local user interaction • Extension to the device software

17. Name the libraries specified by WML Script.

• Lang • Float • String • URL • WML Browser • Dialogs

18. What are the classes of libraries?

• Common network services • Network specific services • Public services

19. Name the operations performed by PAP.

Push access Protocol performs the following operations: • Push submission • Result notification • Push cancellation • Status query • Client capabilities query

20. What are the components of WAP2.0?

The protocol framework of WAP2.0 consists of four components: • Bearer networks • Transport services • Transfer services • Session services

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21. What is the use of congestion threshold?

The exponential growth of the congestion window in the slow start mechanism is dangerous as it doubles the congestion window at each step. So a congestion threshold is set at which the exponential growth stops.

22. What is image scaling? If a page contains a true color, high-resolution picture, this picture can be

called 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.

23. Define WAP

WAP is Wireless Application Protocol. It is the basic Objective of the WAP forum are to bring diverse Internet content and others data service to digital cellular phones and other wireless, mobile terminals. More ever a protocol suite should enable global wireless communication across different wireless network technologies. All WAP forum solution must be: interoperable, scalable, efficient, and reliable.

24. What is WML Browser?

WML Browser is a library that provides several functions typical for a browser, such as per to go back one card or refresh to update the context of the user interface.

25. What are the features of WML?

WML includes several basic features. i) Text and Images ii)User Interaction iii)Navigation iv)Context Management

26. 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.

27. 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 roundtrip time (RTT).This is called the exponential growth of the congestion window.

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28. 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.

29. 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.

30. How does data transmission takes place?

Data transmission takes place using network adapters, fiber optics, copper wires, special hardware for routers etc.

31. Mention two WAP service provides. Find two cell phones supporting WAP and identify which WAP version they support.

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

32. How and why does I-TCP isolate problems on the wireless link? What are the main drawbacks of this solution?

The loss of the end to end semantics of TCP causes problems if the foreign agent portioning the TCP connection crashes. 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.

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33. Can the problems using TCP for mobile communication be solved by replacing TCP with snooping TCP? Justify your answer.

Ans: yes buffering of packets sent to the mobile host lost packets on the wireless link

(both retransmitted immediately by the mobile host ordirections!) will be foreign agent, respectively (so called .local. retransmission)

the foreign agent therefore .snoops. the packet flow and recognizes acknowledgements in both directions, it also filters ACKs

changes of TCP only within the foreign agent

34. What are the key elements of the WAP specification? Networks and Network Bearers TCP/IP as Transport Protocol Processors

35. What are the goals of WTLS layer? It provides the upper-level layer of WAP with a secure transport service

interface that preserves the transport service interface below it. In addition, WTLS provides an interface for managing (e.g., creating and terminating) secure connections. It provides functionality similar to TLS 1.0 and incorporates additional features such as datagram support, optimized handshake and dynamic key refreshing.

36. 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).

37. What are Advantage and Disadvantage of Mobile TCP?

Advantage: i. M-TCP maintains the TCP end-to-end semantic. 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.

MOBILE COMPUTING

38. What is fast retransmit?

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 packet before the timer expires. This behavior is called fast retransmit.

39. 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.

40. 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.

41. 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. Waiting time depends on the time between the first and the best announcement.

42. Define WDP.

WDP is Wireless Datagram Protocol operates on top of many different bearer services capable of carry in data. At the T-SAP WDP offers a consistent datagram transport service independent of the underlying bearer.WDP offers source and destination port numbers used for multiplexing and demultiplexing of data respectively.

43. What are the three ways of WTA extends the WAE application model?

i) Content push: A WTA organ server can push the content. ii) Handling of network events: A device can have a table indicating how to react to certain events from the mobile network. iii) Access to telephony function: Application running on the client can access telephony functions from WML or WML script is very simple.