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UNIT I
WIRELESS COMMUNICATION FUNDAMENTALS
Introduction – Wireless transmission – Frequencies for radio transmission – Signals – Antennas – Signal Propagation –
Multiplexing – Modulations – Spread spectrum – MAC – SDMA – FDMA – TDMA – CDMA – Cellular Wireless
Networks.
INTRODUCTION
Mobile computing means different things to different people. Ubiquitous, wireless and remote computing Wireless and
mobile computing are not synonymous. Wireless is a transmission or information transport method that enables mobile
computing.
Aspects of mobility:
user mobility: users communicate (wireless) “anytime, anywhere, with anyone”
device portability: devices can be connected anytime, anywhere to the network
Mobility Issues
Bandwidth restrictions and variability
Location-aware network operation
o User may wake up in a new environment
o Dynamic replication of data
Querying wireless data & location-based responses
Busty network activity during connections & handling disconnections
Disconnection
o OS and File System Issues - allow for disconnected operation
o Database System Issues - when disconnected, based on local data
Portability Issues
Battery power restrictions
Risks to data
- Physical damage, loss, theft
- Unauthorized access
- encrypt data stored on mobiles
- Backup critical data to fixed (reliable) hosts
Small user interface
- Small displays due to battery power and aspect ratio constraints
- Cannot open too many windows
- Difficult to click on miniature icons
- Input - Graffiti, (Dictionary-based) Expectation
- Gesture or handwriting recognition with Stylus Pen Voice matching or voice recognition
APPLICATIONS
Vehicles
transmission of news, road condition, weather, music via DAB
personal communication using GSM
position via GPS
local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy
vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance
Emergencies
early transmission of patient data to the hospital, current status, first diagnosis
Replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc.
crisis, war, ...
Travelling salesmen
direct access to customer files stored in a central location
consistent databases for all agents
mobile office
Replacement of fixed networks
remote sensors, e.g., weather, earth activities
flexibility for trade shows
LANs in historic buildings
Entertainment, education,
outdoor Internet access
intelligent travel guide with up-to-date location dependent information
ad-hoc networks for multi user games
Location dependent services
Location aware services
what services, e.g., printer, fax, phone, server etc. exist in the local environment
Follow-on services
automatic call-forwarding, transmission of the actual workspace to the current location
Information services
„push“: e.g., current special offers in the supermarket
„pull“: e.g., where is the Black Forrest Cherry Cake?
Support services
caches, intermediate results, state information etc. „follow“ the mobile device through the fixed network
Privacy
who should gain knowledge about the location
Effects of device portability
Power consumption
limited computing power, low quality displays, small disks due to limited battery capacity
CPU: power consumption ~ CV2f
C: internal capacity, reduced by integration
V: supply voltage, can be reduced to a certain limit
f: clock frequency, can be reduced temporally
Loss of data
higher probability, has to be included in advance into the design (e.g., defects, theft)
Limited user interfaces
compromise between size of fingers and portability
integration of character/voice recognition, abstract symbols
Limited memory
limited value of mass memories with moving parts
Flash-memory or? as alternative
Wireless networks in comparison to fixed networks
Higher loss-rates due to interference
emissions of, e.g., engines, lightning
Restrictive regulations of frequencies
frequencies have to be coordinated, useful frequencies are almost all occupied Low transmission rates
local some Mbit/s, regional currently, e.g., 9.6kbit/s with GSM .Higher delays, higher jitter
connection setup time with GSM in the second range, several hundred milliseconds for other wireless
systems
Lower security, simpler active attacking
radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile
phones
Always shared medium
secure access mechanisms important
Early history of wireless communication
Many people in history used light for communication
heliographs, flags („semaphore“), ...
150 BC smoke signals for communication; (Polybius, Greece)
1794, optical telegraph, Claude Chappe
Here electromagnetic waves are of special importance:
1831 Faraday demonstrates electromagnetic induction
J. Maxwell (1831-79): theory of electromagnetic Fields, wave equations (1864)
H. Hertz (1857-94): demonstrates with an experiment the wave character of electrical transmission
through space(1886, in Karlsruhe, Germany, at the location of today’s University of Karlsruhe)
Wireless systems: overview of the development
cellular phones satellites wireless
LAN
cordless
phones
1992:
GSM
1994:
DCS 1800
2005?:
UMTS/IMT-2000
1987:
CT1+
1982:
Inmarsat-A
1992:
Inmarsat-B
Inmarsat-M
1998:
Iridium
1989:
CT 2
1991:
DECT
199x:
proprietary
1995/96/97:
IEEE 802.11,
HIPERLAN
2005?:
MBS, WATM
1988:
Inmarsat-C
analog
digital
1991:
D-AMPS
1991:
CDMA
1981:
NMT 450
1986:
NMT 900
1980:
CT0
1984:
CT11983:
AMPS
1993:PDC
Areas of research in mobile communication
Wireless Communication
transmission quality (bandwidth, error rate, delay)
modulation, coding, interference
media access, regulations
Mobility
location dependent services
location transparency
quality of service support (delay, jitter, security)
Portability
power consumption
limited computing power, sizes of display, ...
usability
Simple reference model used here
Influence of mobile communication to the LAYER MODEL
Application layer
service location
new applications, multimedia
adaptive applications
Transport layer
congestion and flow control
quality of service
Network layer
addressing, routing, device location
hand-over
Data link layer
authentication
media access
multiplexing
media access control
Physical layer
encryption
modulation
interference
attenuation
frequency
WIRELESS TRANSMISSION - FREQUENCIES FOR RADIO TRANSMISSION
Frequencies for communication
Frequencies for mobile communication
VHF-/UHF-ranges for mobile radio
simple, small antenna for cars
deterministic propagation characteristics, reliable connections
SHF and higher for directed radio links, satellite communication
small antenna, focusing
large bandwidth available
Wireless LANs use frequencies in UHF to SHF spectrum
some systems planned up to EHF
limitations due to absorption by water and oxygen molecules (resonance frequencies)
Weather dependent fading, signal loss caused by heavy rainfall etc.
Frequencies and regulations
ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)
Europe USA Japan
Mobile phones
NMT 453-457MHz, 463-467 MHz; GSM 890-915 MHz,
935-960 MHz; 1710-1785 MHz, 1805-1880 MHz
AMPS, TDMA, CDMA 824-849 MHz, 869-894 MHz; TDMA, CDMA, GSM 1850-1910 MHz, 1930-1990 MHz;
PDC 810-826 MHz, 940-956 MHz; 1429-1465 MHz, 1477-1513 MHz
Cordless telephones
CT1+ 885-887 MHz, 930-932 MHz; CT2 864-868 MHz DECT
1880-1900 MHz
PACS 1850-1910 MHz, 1930-1990 MHz PACS-UB 1910-1930 MHz
PHS 1895-1918 MHz JCT 254-380 MHz
Wireless LANs
IEEE 802.11
2400-2483 MHz HIPERLAN 1 5176-5270 MHz
IEEE 802.11
2400-2483 MHz
IEEE 802.11
2471-2497 MHz
SIGNALS
physical representation of data
function of time and location
signal parameters: parameters representing the value of data
classification
o continuous time/discrete time
o continuous values/discrete values
o analog signal = continuous time and continuous values
o digital signal = discrete time and discrete values
signal parameters of periodic signals:
period T, frequency f=1/T, amplitude A, phase shift
sine wave as special periodic signal for a carrier:
s(t) = At sin(2 ft t + t)
Fourier representation of periodic signals
1
0
1
0
t t
Ideal periodic signal Real composition (based on
harmonics)
Different representations of signals
amplitude (amplitude domain)
frequency spectrum (frequency domain)
phase state diagram (amplitude M and phase in polar coordinates)
Composed signals transferred into frequency domain using Fourier transformation
Digital signals need
infinite frequencies for perfect transmission
Modulation with a carrier frequency for transmission (analog signal!)
ANTENNAS
Isotropic radiator
Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission
Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna
Real antennas always have directive effects (vertically and/or horizontally)
Radiation pattern: measurement of radiation around an antenna
)2cos()2sin(2
1)(
11
nftbnftactgn
n
n
n
Ideal isotropic radiator
Simple dipoles
Real antennas are not isotropic radiators but, e.g., dipoles with lengths /4 on car roofs or /2 as Hertzian dipole,
shape of antenna proportional to wavelength
Example: Radiation pattern of a simple Hertzian dipole
Directed and Sectorized
Often used for microwave connections or base stations for mobile phones (e.g., radio coverage of a valley)
/2
z y
x
z
y x
/4
Antennas: diversity
Grouping of 2 or more antennas
o multi-element antenna arrays
Antenna diversity
o switched diversity, selection diversity
receiver chooses antenna with largest output
diversity combining
combine output power to produce gain
cophasing needed to avoid cancellation
SIGNAL PROPAGATION
Transmission range
communication possible
low error rate
Detection range
detection of the signal possible
no communication possible
Interference range
signal may not be detected
signal adds to the background noise
Signal propagation
Propagation in free space always like light (straight line)
Receiving power proportional to 1/d²
(d = distance between sender and receiver)
Receiving power additionally influenced by
fading (frequency dependent)
shadowing
reflection at large obstacles
scattering at small obstacles
diffraction at edges
+
/4 /4
/2
/2
+
/2
Shadowing Reflection Scattering Diffraction
Multipath propagation
Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction
Time dispersion: signal is dispersed over time
Interference with “neighbor” symbols, Inter Symbol Interference (ISI)
The signal reaches a receiver directly and phase shifted
Distorted signal depending on the phases of the different parts
Effects of mobility
Channel characteristics change over time and location
signal paths change
different delay variations of different signal parts
different phases of signal parts
Quick changes in the power received (short term fading)
Additional changes in
distance to sender
obstacles further away
Slow changes in the average power received (long term fading)
MULTIPLEXING
Multiplexing in 4 dimensions
space (si)
time (t)
frequency (f)
code (c)
Frequency Division Multiplexing - FDM
The oldest used technique used for multiplexing. Possible when the useful bandwidth of the medium exceeds that of the
signals it has to carry. Each signal is modulated on a different carrier frequency. This results in shifting the spectrum of
the signal around the carrier frequency. Sufficient guard-band is given so those neighboring signals do not overlap in the
frequency domain.
At the receiving end each signal is extracted by first passing it through a band-pass filter and then demodulating with the
same carrier frequency that was used to modulate the signal. The signals carried using FDM may be analog signals or may
be analog signals representing digital data. However FDM is mostly a technique from the era of analog communications.
In FDM a device uses some of the channel all of the time. FDM is used in radio and television broadcasting. FDM is also
used in high capacity long distance links in the telephone network.
Frequency division multiplexing (FDM) achieves multiplexing by using different carrier frequencies .Receiver can "tune"
to specific frequency and extract modulation for that one channel .Frequencies must be separated to avoid interference -
“Wastes” potential signal bandwidth for guard channels.Only useful in media that can carry multiple signals with different
frequencies - high-bandwidth required .
Used in:
The standard of the analog telephone network
The standard in radio broadcasting
The standard for video
1. Broadcast
2. Cable
3. Satellite
Frequency Division Multiplexing Diagram
Time Division Multiplexing - TDM
Time division multiplexing is more suitable for digital data. TDM can be used when the data rate available on a
communication link exceeds the data rate required by any one of the sources. In TDM each source that is to use the link
fills up a buffer with data. A TDM multiplexer scans the buffers in some predetermined order and transmits bits from
each source one after the other.
Requires digital signaling & transmission
Requires data rate = sum of inputs + framing
Data rate much higher than equivalent analog bandwidth uses
Separates data streams in time not frequency
The standard of the modern digital telephone system
Code Division Multiplexing - CDM
Each channel has a unique code. All channels use the same spectrum at the same time.
Advantages:
bandwidth efficient
no coordination and synchronization necessary
good protection against interference and tapping
Disadvantages:
lower user data rates
more complex signal regeneration
C
T
F
k2 k1 k3 k4 k5 k6
MODULATIONS
Digital modulation
o digital data is translated into an analog signal (baseband)
o ASK, FSK, PSK - main focus in this chapter
o differences in spectral efficiency, power efficiency, robustness
Analog modulation
o shifts center frequency of baseband signal up to the radio carrier Motivation
o smaller antennas (e.g., /4)
o Frequency Division Multiplexing
o medium characteristics
Basic schemes
o Amplitude Modulation (AM)
o Frequency Modulation (FM)
o Phase Modulation (PM)
Modulation and demodulation
Digital modulation
Modulation of digital signals known as Shift Keying.
Amplitude Shift Keying (ASK):
very simple
low bandwidth requirements
very susceptible to interference
Frequency Shift Keying (FSK):
needs larger bandwidth
Phase Shift Keying (PSK):
more complex
robust against interference
Advanced Frequency Shift Keying
bandwidth needed for FSK depends on the distance between the carrier frequencies
special pre-computation avoids sudden phase shifts
MSK (Minimum Shift Keying)
bit separated into even and odd bits, the duration of each bit is doubled
depending on the bit values (even, odd) the higher or lower frequency, original or inverted is chosen
the frequency of one carrier is twice the frequency of the other
even higher bandwidth efficiency using a Gaussian low-pass filter
GMSK (Gaussian MSK), used in GSM.
Advanced Phase Shift Keying
BPSK (Binary Phase Shift Keying):
bit value 0: sine wave
bit value 1: inverted sine wave
very simple PSK
low spectral efficiency
robust, used e.g. in satellite systems
QPSK (Quadrature Phase Shift Keying):
2 bits coded as one symbol
symbol determines shift of sine wave
needs less bandwidth compared to BPSK
more complex
Often also transmission of relative, not absolute phase shift: DQPSK - Differential QPSK (IS-136, PACS, PHS
BPSK (Binary Phase Shift Keying):
QPSK (Quadrature Phase Shift Keying):
Quadrature Amplitude Modulation
Quadrature Amplitude Modulation (QAM): combines amplitude and phase modulation
it is possible to code n bits using one symbol
2n discrete levels, n=2 identical to QPSK
bit error rate increases with n, but less errors compared to comparable PSK schemes
SPREAD SPECTRUM
Effects of spreading and interference
DSSS (Direct Sequence Spread Spectrum)
XOR of the signal with pseudo-random number (chipping sequence)
many chips per bit (e.g., 128) result in higher bandwidth of the signal
Advantages
reduces frequency selective fading
in cellular networks
o base station scan use the same frequency range several base stations can detect and recover the signal
o soft handover
Q
I
11
01
10
00
Q
I 0 1
Disadvantages
precise power control necessary
FHSS (Frequency Hopping Spread Spectrum)
Discrete changes of carrier frequency
sequence of frequency changes determined via pseudo random number sequence
Two versions
Fast Hopping:
several frequencies per user bit
Slow Hopping:
several user bits per frequency
Advantages
frequency selective fading and interference limited to short period
simple implementation
uses only small portion of spectrum at any time
Disadvantages
not as robust as DSSS
simpler to detect
FHSS (Frequency Hopping Spread Spectrum)
Frequency Hopping Spread Spectrum
Medium Access Control (MAC)
MAC protocol which were developed for nodes at short distance did not show good performance for nodes at longer
distance so another protocol has to be developed Known as 2p MAC Protocol.
802.11 protocols were good for devices which had no power supply issue frequent charging were available to them etc.
1. This protocol based devices were not good for certain operation like monitoring the natural habitat of wildlife.
2. Sampling the water level of dam.
These applications do not require frequent human intervention and are required to run for a longer duration.
To fulfill the requirement other protocol was developed sensor network (802.15.4)
Energy Budgets:-Main points which were discussed in this were how its protocol helps in saving power by
cleverly managing the time when device should sleep when to wake up.
MAC protocol used in 802.15.4.
Routing and tree formation in ZigBee: - Routing protocol was developed by Zigbee firm.
Wireless MAC Issues
Wireless medium makes the MAC design more challenging than the wireline networks.
The three important issues are:
1. Half Duplex operation –> either send or receive but not both at a given time
2. Time varying channel
3. Burst channel errors
1. Half Duplex Operation
In wireless, it’s difficult to receive data when the transmitter is sending the data, because:
When node is transmitting, a large fraction of the signal energy leaks into the receiver path
The transmitted and received power levels can differ by orders of magnitude
The leakage signal typically has much higher power than the received signal ->“Impossible to detect a
received signal, while transmitting data”
Collision detection is not possible, while sending data
As collision cannot be detected by the sender, all proposed protocols attempt to minimize the probability of collision
-> Focus on collision avoidance
2. Time Varying Channel
Three mechanisms for radio signal propagation
Reflection – occurs when a propagating wave impinges upon an object that has very large dimensions than the
wavelength of the radio wave e.g. reflection occurs from the surface of the earth and from buildings and walls
Diffraction – occurs when the radio path between the transmitter and the receiver is obstructed by a surface
with sharp edges
Scattering – occurs when the medium through which the wave travels consists of objects with
The received signal by a node is a superposition of time-shifted and attenuated versions of the ransmitted signals the
received signal varies with time .The time varying signals (time varying channel) phenomenon also known as multipath
propagation. The rate of variation of channel is determined by the coherence time of the hannel Coherence time is defined
as time within which When a node’s received signal strength drops below a certain threshold the node is said to be in fade
.Handshaking is widely used strategy to ensure the link quality is good enough for data communication. A successful
handshake between a sender and a receiver (small message) indicates a good communication link.
3. Burst Channel Errors
As a consequence of time varying channel and varying signals strengths errors are introduced in the transmission (Very
likely) for wire line networks the bit error rate (BER) is the probability of packet error is small .For wire line networks the
errors are due to random For wireless networks the BER is as high.For wireless networks the errors are due to node being in
fade as a result errors occur in a long burst. Packet loss due to burst errors - mitigation techniques
» Smaller packets
» Forward Error Correcting Codes
» Retransmissions (Acks)
Location Dependent Carrier Sensing
Location Dependent Carrier Sensing results in three types of nodes that protocols need to deal with:
Hidden Nodes
Even if the medium is free near the transmitter, it may not be free near the intended receiver
Exposed Nodes
Even if the medium is busy near the transmitter, it may be free near the intended receiver
Capture
Capture occurs when a receiver can cleanly receive a transmission from one of two simultaneous transmissions
Hidden Node/Terminal Problem
A hidden node is one that is within the range of the intended destination but out of range of sender Node B can
communicate with A and C both A and C cannot hear each other When A transmits to B, C cannot detect the
transmission using the carrier sense mechanism C falsely thinks that the channel is idle
Exposed Nodes
An exposed node is one that is within the range of the sender but out of range of destination .when a node’s received signal
strength drops below a certain threshold the node is said to be in fade .Handshaking is widely used strategy to ensure the
link quality is good enough for data communication. A successful handshake between a sender and a receiver (small
message) indicates a good communication link.
In theory C can therefore have a parallel transmission with any node that cannot hear the transmission from B, i.e. out
of range of B. But C will not transmit to any node because it’s an exposed node. Exposed nodes waste bandwidth.
Capture
Capture is said to occur when a receiver can cleanly receive a transmission from one of two simultaneous transmissions both
within its range Assume node A and D transmit simultaneously to B. The signal strength received from D is much higher
than that from A, and D’s transmission can be decoded without errors in presence of transmissions from A.D has captured A.
Capture is unfair because it gives preference to nodes that are closer to the receiver. It may improve protocol performance
MULTIPLE ACCESS
FDMA
It is an ANALOQUE technique in time. Synchronization the transmission bandwidth is partitioned to frequency slots
different users has different RF carrier frequencies, i.e. Each user is assigned a particular frequency slot.
users/signals are at the receiver by separated out FILTERING if all frequency slots are occupied then the system has
reached its.
TDMA
It is a DIGITAL technique requires between users synchronization each user/signal is assigned a particular (within
a time-frame) time slot.
CELLULAR WIRELESS NETWORKS
Implements space division multiplex: base station covers a certain transmission area (cell).Mobile stations communicate
only via the base station
Advantages of cell structures:
higher capacity, higher number of users
less transmission power needed
more robust, decentralized
base station deals with interference, transmission area etc. locally
Problems:
fixed network needed for the base stations
handover (changing from one cell to another) necessary
interference with other cells
Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM) - even less for higher frequencies
Frequency reuse only with a certain distance between the base stations
Standard model using 7 frequencies:
Fixed frequency assignment:
certain frequencies are assigned to a certain cell
problem: different traffic load in different cells
Dynamic frequency assignment:
base station chooses frequencies depending on the frequencies already used in neighbor cells
more capacity in cells with more traffic
assignment can also be based on interference measurements
3 cell cluster 3 cell cluster with 3 sector antennas
f4 f5
f1 f3
f2
f6
f7
f3 f2
f4 f5
f1
Cell : Why Hexagon?
• In reality the cell is an irregular shaped circle, for design convenience and as a first order approximation, it is
assumed to be regular polygons
• The hexagon is used for two reasons:
– A hexagonal layout requires fewer cells, therefore, fewer transmission site
– Less expensive compared to square and triangular cells
• Irregular cell shape leads to inefficient use of the spectrum because of inability to reuse frequency on account of
co channel interference uneconomical deployment of equipment, requiring relocation from one cell site to
another
UNIT I WIRELESS COMMUNICATION FUNDAMENTALS
Part- A
1. Define SAMA.
Spread Aloha Multiple Access is a combination of CDMA and TDMA. The
CDMA better suits for connection oriented services only and not for connection less
bursty data traffic because it requires to program both sender and receiver to access
different users with different codes.
2. Define CDMA.
Code Division Multiple Access systems use codes with certain characteristics to separate
different users. To enable access to the shared medium without interference. The users
use the same frequency and time to transmit data. The main problem is to find good
codes and to separate this signal from noise. The good code can be found the following 2
characteristic 1.Orthogonal, 2.AutoCorrelation.
3. What are the several versions in CSMA?
There are several versions in CSMA, they are as follows
a) Non-persistent CSMA
b) p-persistent CSMA
c) 1-persistent CSMA
4. What is meant by non-persistent CSMA?
In, non-persistent CSMA, stations sense the carrier and start sending immediately
if the medium is idle., if the medium is busy, the station pauses a random amount of time
before sensing the medium again and repeating this pattern.
5. What is meant by p-persistent CSMA?
In p-persistent CSMA system nodes also sense the medium, but only transmit with a
probability of p. With the station deferring to the next slot with the probability 1-p,
i.e. access is slotted in addition.
6. What is SDMA?
Space Division Multiple Access (SDMA) is used for allocating separated spaces to users
in wireless networks. The basis for the SDMA algorithm is formed by cells and
sectorized antennas which constitute the infrastructure implementing space division
multiplexing (SDM)
7. What is FDD?
In FDMA, the base station and the mobile station establish a duplex channel. The two
directions, mobile station to base station and vice versa are separated using different
frequencies. This Scheme is called Frequency Division Duplex (FDD)
8. What are the 2 sub layers in DLC?
Logical Link Control (LLC)
Media Access Control (MAC)
9. List out the advantages of frequency division multiplexing.
no dynamic coordination necessary
works also for analog signals
10. List out the disadvantages of frequency division multiplexing.
waste of bandwidth if the traffic is distributed unevenly
inflexible
guard spaces
11. Define time division multiplexing.
A channel gets the whole spectrum for a certain amount of time
12. List out the advantages of time division multiplexing.
only one carrier in the
medium at any time
throughput high even
for many users
13. List out the disadvantages of time division multiplexing.
precise
synchronization
necessary
14. Define code division multiplexing.
Each channel has a unique code
All channels use the same spectrum at the same time
15. Define Signal
physical representation of data
function of time and location
signal parameters: parameters representing the value of data
16. Define Analog modulation.
shifts center frequency of base band signal up to the radio carrier
17. What is Quadrature Amplitude Modulation? Quadrature Amplitude Modulation (QAM): combines amplitude and phase modulation
it is possible to code n bits using one symbol
2n discrete levels, n=2 identical to QPSK
bit error rate increases with n, but less errors compared to comparable PSK schemes
18. What is digital modulation?
* Digital data is translated into an analog signal (baseband)
* ASK, FSK, PSK - main focus in this chapter
* Differences in spectral efficiency, power efficiency, robustness
UNIT1 - WIRELESS COMMUNICATION FUNDAMENTALS
Part B
1. Explain different TDMA schemes in detail.
Fixed TDMA, Classical TDMA, Slotted TDMA, Carrier sense multiple access, Demand
assigned multiple access, PRMA Packet reservation multiple access, Reservation multiple
access, Reservation TDMA, Multiple access with collision avoidance, Polling, Inhibit sense
multiple access.
2. Explain multiplexing in detail.
Frequency multiplex
Time multiplex
Code multiplex
3. Discuss Modulation techniques in detail.
Digital modulation
Analog modulation
Basic schemes
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
4. Account on CDMA Scheme.
Good code, Orthogonal, Autocorrelation, Spread aloha multiple access.
5. Explain FDMA in detail
Segment the frequency band into
Disjoint sub-bands.
Terminals
Signal
Separation
Advantages
Disadvantages
6. Discuss SDMA in detail
segment space into cells/sectors
Terminals
Signal
Separation
Advantages
Disadvantages
7.Explain major types of networks.
Satellite-based networks
Cellular networks
Cordless systems
Fixed wireless access schemes
8. Explain types of Antennas in detail.
Isotropic antenna (idealized)
Radiates power equally in all directions
Dipole antennas
WhtHalf-wave dipole antenna (or Hertz antenna)
Quarter-wave vertical antenna (or Marconi antenna)
Parabolic Reflective Antenna
9. Explain the various applications of mobile computing.
Various applications and explanation
1
IT1402 -MOBILE COMPUTING
UNIT II
TELECOMMUNICATION NETWORKS
Telecommunication systems – GSM – GPRS – DECT – UMTS – IMT-2000 – Satellite Networks - Basics –
Parameters and Configurations – Capacity Allocation – FAMA and DAMA – Broadcast Systems – DAB - DVB.
Telecommunication systems -GSM – GPRS – DECT – UMTS – IMT-2000
Building Blocks
• AMPS – Advanced Mobile Phone System
• TACS – Total Access Communication System
• NMT – Nordic Mobile Telephone System
AMPS – Advanced Mobile Phone System
• analog technology
• used in North and South America and approximately 35 other countries
• operates in the 800 MHz band using FDMA technology
TACS – Total Access Communication System
• variant of AMPS
• deployed in a number of countries
• primarily in the UK
NMT – Nordic Mobile Telephone System
• analog technology
• deployed in the Benelux countries and Russia
• operates in the 450 and 900 MHz band
• first technology to offer international roaming – only within the Nordic countries
2
System Architecture
Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
Base Station Subsystem (BBS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Network Subsystem
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
• Mobile Station: is a subscriber unit intended for use while on the move at unspecified locations. It could be a
hand-held or a portable terminal.
• Base Station: a fixed radio station used for communication with MS. It is located at the centre of a cell and
consist of Transmitters and Receivers.
• Mobile Switching Centre: it coordinates the routing of calls, do the billing, etc.
Mobile Station (MS)
The Mobile Station is made up of two entities:
1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)
Mobile Equipment
• Produced by many different manufacturers
• Must obtain approval from the standardization body
• Uniquely identified by an IMEI (International Mobile Equipment Identity)
Base Transceiver Station (BTS)
Base Transceiver Station
(BTS)
Base Station Controller
(BSC)
Abis interface Base Station (BS)
Base Transceiver Station
(BTS)
Base Transceiver Station
(BTS)
Base Station Controller
(BSC)
Mobile Stations (MS)
Um interface
A interface
Base Station (BS)
Abis interface
CCITT Signalling
System No. 7 (SS7)
interface
Mobile Switchin
g Centre (MSC)
GMSC
PSTN
VLR
HLR
3
Subscriber Identity Module (SIM)
• Smart card containing the International Mobile Subscriber Identity (IMSI)
• Allows user to send and receive calls and receive other subscribed services
• Encoded network identification details
• Protected by a password or PIN
• Can be moved from phone to phone – contains key information to activate the phone
Base Station Subsystem (BBS)
Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing
operation between components made by different suppliers
1. Base Transceiver Station (BTS)
1. Base Station Controller (BSC)
Base Transceiver Station (BTS)
• Houses the radio transceivers that define a cell
• Handles radio-link protocols with the Mobile Station
• Speech and data transmissions from the MS are recoded
• Requirements for BTS:
o ruggedness
o reliability
o portability
o minimum costs
Base Station Controller (BSC)
• Manages Resources for BTS
• Handles call set up
• Location update
• Handover for each MS
Network Subsystem
Mobile Switching Center (MSC)
• Switch speech and data connections between:
Base Station Controllers
Mobile Switching Centers
GSM-networks
Other external networks
• Heart of the network
• Three main jobs:
1) Connects calls from sender to receiver
2) Collects details of the calls made and received
3) Supervises operation of the rest of the network components
Home Location Registers (HLR)
- contains administrative information of each subscriber
- Current location of the mobile
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Visitor Location Registers (VLR)
- contains selected administrative information from the HLR
- authenticates the user
- tracks which customers have the phone on and ready to receive a call
- periodically updates the database on which phones are turned on and ready to receive calls
Authentication Center (AUC)
- mainly used for security
- data storage location and functional part of the network
- Ki is the primary element
Equipment Identity Register (EIR)
Database that is used to track handsets using the IMEI (International Mobile
Equipment Identity)
- Made up of three sub-classes: The White List, The Black List and the Gray List
- Optional database
Basic Features Provided by GSM
• Call Waiting
- Notification of an incoming call while on the handset
• Call Hold
- Put a caller on hold to take another call
• Call Barring
- All calls, outgoing calls, or incoming calls
• Call Forwarding
- Calls can be sent to various numbers defined by the user
• Multi Party Call Conferencing
- Link multiple calls together
Advanced Features Provided by GSM
• Calling Line ID
- incoming telephone number displayed
• Alternate Line Service
- one for personal calls
- one for business calls
• Closed User Group
- call by dialing last for numbers
• Advice of Charge
- tally of actual costs of phone calls
• Fax & Data
- Virtual Office / Professional Office
• Roaming
- services and features can follow customer from market to market
Advantages of GSM
• Crisper, cleaner quieter calls
• Security against fraud and eavesdropping
• International roaming capability in over 100 countries
• Improved battery life
• Efficient network design for less expensive system expansion
• Efficient use of spectrum
• Advanced features such as short messaging and caller ID
5
• A wide variety of handsets and accessories
• High stability mobile fax and data at up to 9600 baud
• Ease of use with over the air activation, and all account information is held in a smart card which can be
moved from handset to handset
UMTS (Universal Mobile Telephone System
• Reasons for innovations
- new service requirements
- availability of new radio bands
• User demands
- seamless Internet-Intranet access
- wide range of available services
- compact, lightweight and affordable terminals
- simple terminal operation
- open, understandable pricing structures for the whole spectrum of available services
UMTS Basic Parameter
• Frequency Bands (FDD : 2x60 MHz):
– 1920 to 1980 MHz (Uplink)
– 2110 to 2170 MHz (Downlink)
• Frequency Bands (TDD: 20 + 15 MHz):
– 1900 – 1920 MHz and 2010 – 2025 MHz
• RF Carrier Spacing:
– 4.4 - 5 MHz
• RF Channel Raster:
– 200 KHz
• Power Control Rate:
– 1500 Cycles per Second
UMTS W-CDMA Architecture
6
GPRS
General Packet Radio Service
Definition:
GPRS stands for General Packet Radio Service and is a second generation (2G) and third generation (3G)--
or sometimes refered to as in-between both generations, 2.5G--wireless data service that extends GSM data
capabilities for Internet access, multimedia messaging services, and early mobile Internet applications via
the wireless application protocol (WAP), as well as other wireless data services.
Features of GPRS
GPRS was one of the earliest cell phone data access technologies, and more widespread particularly in
Europe and Asia, though it was adopted by carriers in North America, such as Rogers in Canada and T-
Mobile in the US.
2G (second generation) GPRS service had data rates of 56-114 kbit/second--akin to dial-up modem speeds.
GPRS wireless networks were later enhance faster 3G (third generation) throughput speeds. T-Mobile's
EDGE (enhanced Data Rates for Global Evolution), for example, delivers up to 4 times the GPRS rate.
Both GPRS and Edge, however, are quickly being surpassed by even faster 4G (fourth generation) mobile
data networks.
Examples:
GPRS, which refers to a mobile or wireless data service, is not the same as GPS, which refers to geo-
location. GPRS data networks enable users to access Web data and rich content from their cell phones.
Technical overview
The GPRS core network allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external
networks such as the Internet. The GPRS system is an integrated part of the GSM network switching
subsystem.
Services offered
GPRS extends the GSM Packet circuit switched data capabilities and makes the following services possible:
SMS messaging and broadcasting
"Always on" internet access
Multimedia messaging service (MMS)
Push to talk over cellular (PoC)
Instant messaging and presence—wireless village
Internet applications for smart devices through wireless application protocol (WAP)
Point-to-point (P2P) service: inter-networking with the Internet (IP)
Point-to-Multipoint (P2M) service: point-to-multipoint multicast and point-to-multipoint group calls
7
If SMS over GPRS is used, an SMS transmission speed of about 30 SMS messages per minute may be
achieved. This is much faster than using the ordinary SMS over GSM, whose SMS transmission speed is
about 6 to 10 SMS messages per minute.
Protocols supported
GPRS supports the following protocols:
Internet protocol IP. In practice, built-in mobile browsers use IPv4 since IPv6 was not yet popular.
Point-to-point protocol (PPP). In this mode PPP is often not supported by the mobile phone operator
but if the mobile is used as a modem to the connected computer, PPP is used to tunnel IP to the
phone. This allows an IP address to be assigned dynamically (IPCP not DHCP) to the mobile
equipment.
X.25 connections. This is typically used for applications like wireless payment terminals, although it
has been removed from the standard. X.25 can still be supported over PPP, or even over IP, but
doing this requires either a network based router to perform encapsulation or intelligence built in to
the end-device/terminal; e.g., user equipment (UE).
When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will store and
forward the IP packets to the phone even during handover. The TCP handles any packet loss (e.g. due to a
radio noise induced pause).
Hardware
Devices supporting GPRS are divided into three classes:
Class A
Can be connected to GPRS service and GSM service (voice, SMS), using both at the same time.
Such devices are known to be available today.
Class B
Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at
a given time. During GSM service (voice call or SMS), GPRS service is suspended, and then
resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS
mobile devices are Class B.
Class C
Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually
between one or the other service.
A true Class A device may be required to transmit on two different frequencies at the same time, and thus
will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual
transfer mode (DTM) feature. A DTM-capable mobile may use simultaneous voice and packet data, with
the network coordinating to ensure that it is not required to transmit on two different frequencies at the same
time. Such mobiles are considered pseudo-Class A, sometimes referred to as "simple class A". Some
networks support DTM since 2007
8
DECT
Digital Enhanced Cordless Telecommunications
The base unit and handset of a British Telecom DECT cordless telephone
Digital Enhanced Cordless Telecommunications (Digital European Cordless Telecommunications), usually known by
the acronym DECT, is a digital communication standard, which is primarily used for creating cordless phone systems.
It originated in Europe, where it is the universal standard, replacing earlier cordless phone standards, such as
900 MHz CT1 and CT2.
Beyond Europe, it has been adopted by Australia, and most countries in Asia and South America. North American
adoption was delayed by United States radio frequency regulations. This forced development of a variation of DECT,
called DECT 6.0, using a slightly different frequency range; the technology is nearly identical, but the frequency
difference makes the technology incompatible with systems in other areas, even from the same manufacturer. DECT
has almost universally replaced other standards in most countries where it is used, with the exception of North
America.
DECT is used primarily in home and small office systems, but is also available in many PBX systems for medium and
large businesses. DECT can also be used for purposes other than cordless phones. Voice applications, such as baby
monitors, are becoming common. Data applications also exist, but have been eclipsed by Wi-Fi. 3G cellular also
competes with both DECT and Wi-Fi for both voice and data. Nowadays you can find DECT as well in special
applications like Remote Controls for industrial applications.
DECT handsets and bases from different manufacturers typically work together at the most basic level of
functionality: making and receiving calls. The DECT standard includes a standardized interoperability profile for
simple telephone capabilities, called GAP, which most manufacturers implement. The standard also contains several
other interoperability profiles, for data and for radio local-loop services.
Application
The DECT standard fully specifies a means for a portable unit, such as a cordless telephone, to access a fixed
telecoms network via radio. But, unlike the GSM standards, does not specify any internal aspects of the fixed network
itself. Connectivity to the fixed network (which may be of many different kinds) is done through a base station or
"Radio Fixed Part" to terminate the radio link, and a gateway to connect calls to the fixed network. In most cases the
gateway connection is to the public switched telephone network or telephone jack, although connectivity with newer
technologies such as Voice over IP has become available. There are also other devices such as some baby monitors
utilizing DECT, and in these devices there is no gateway functionality. The DECT standard originally envisaged three
major areas of application:
Domestic cordless telephony, using a single base station to connect one or more handsets to the public
telecoms network.
Enterprise premises cordless PABXs and wireless LANs, using many base stations for coverage. Calls
continue as users move between different coverage cells, through a mechanism called handover. Calls can be
both within the system and to the public telecoms network.
Public access, using large numbers of base stations to provide high capacity building or urban area coverage
as part of a public telecoms network.
Of these, the domestic application (cordless home telephones) has been extremely successful. The enterprise PABX
market had some success, and all the major PABX vendors have offered DECT access options. The public access
application did not succeed, since public cellular networks rapidly out-competed DECT by coupling their ubiquitous
coverage with large increases in capacity and continuously falling costs. There has been only one major installation of
DECT for public access: in early 1998 Telecom Italia launched a DECT network known as "Fido" after much
9
regulatory delay, covering major cities in Italy. The service was promoted for only a few months and, having peaked
at 142,000 subscribers, was shut down in 2001.
DECT has also been used for Fixed Wireless Access as a substitute for copper pairs in the "last mile" in countries
such as India and South Africa. By using directional antennas and sacrificing some traffic capacity, cell coverage
could extend to over 10 km. In Europe the power limit laid down for use of the DECT spectrum (250 mW peak) was
expressed in ERP, rather than the more commonly-used EIRP, permitting the use of high-gain directional antennas to
produce much higher EIRP and hence long ranges.
The standard is also used in electronic cash terminals, traffic lights, and remote door openers.
Features
Typical abilities of a domestic DECT Generic Access Profile (GAP) system include:
Multiple handsets to one base station and one phone line socket. This allows several cordless telephones to be
placed around the house, all operating from the same telephone jack. Additional handsets have a battery
charger station which does not plug into the telephone system. Handsets can in many cases be used as
intercoms, communicating between each other, and sometimes as walkie-talkies, intercommunicating without
telephone line connection.
Interference-free wireless operation to around 100 metres (109 yards) outdoors, much less indoors when
separated by walls. Operates clearly in common congested domestic radio traffic situations, for instance,
generally immune to interference from other DECT systems, Wi-Fi networks, video senders, Bluetooth
technology, baby monitors and other wireless devices.
Talk-time of several hours and standby time of several days on one battery charge.
Some systems offer:
A longer range between the telephone and base station (usable further from the base)
Extended battery talk-time, sometimes up to 24 hours
Technical properties
Some DECT properties:
Audio codec: G.726, G.711, G.722 (wideband), G.729.1 (wideband) and MPEG-4 ER LD AAC (wideband
and super-wideband)
Net bit rate: 32 kbit/s
Frequency: 1880 MHz–1900 MHz in Europe, 1900 MHz-1920 MHz in China,1893 MHz–1906 MHz in
Japan, 1910 MHz-1930 MHz in Latin America and 1920 MHz–1930 MHz in the US and Canada, US DECT
and DECT 6 products may NOT be used in the UK or Ireland as they cause and suffer from interference with
the UK & Ireland 3G cellular networks with unlicensed use of such products being prohibited by UK
agencies. As DECT and DECT 6.0 do not operate in the 2.4 GHz ISM band, they are not subject to the
interference arising in this band from its use by 802.11b and 802.11g WiFi, and 2.4 GHz cordless phones.
Carriers: 10 (1.728 MHz spacing) in Europe, 5 (1.728 MHz spacing) in the US
Time slots: 2 x 12 (up and down stream)
Channel allocation: dynamic
Average transmission power: 10 mW (250 mW peak) in Europe, 4 mW (100 mW peak) in the US
The DECT physical layer uses:
Frequency division multiple access (FDMA),
Time division multiple access (TDMA) and
Time division duplex (TDD)
10
This means that the radio spectrum is divided into physical channels in two dimensions: frequency and time.
The maximum allowed power for portable equipment as well as base stations is 250 mW. A portable device radiates
an average of about 10 mW during a call as it is only using one of 24 time slots to transmit.
The DECT media access control layer controls the physical layer and provides connection oriented, connectionless
and broadcast services to the higher layers.
The DECT data link layer uses LAPC (Link Access Protocol Control), a specially designed variant of the ISDN data
link protocol called LAPD. They are based on HDLC.
The DECT network layer always contains the following protocol entities:
Call Control (CC)
Mobility Management (MM)
Optionally it may also contain others:
Call Independent Supplementary Services (CISS)
Connection Oriented Message Service (COMS)
Connectionless Message Service (CLMS)
All these communicate through a Link Control Entity (LCE).
The call control protocol is derived from ISDN DSS1, which is a Q.931 derived protocol. Many DECT-specific
changes have been made. The mobility management protocol includes many elements similar to the GSM protocol,
but also includes elements unique to DECT.
Unlike the GSM protocol, the DECT network specifications do not define cross-linkages between the operation of the
entities (for example, Mobility Management and Call Control). The architecture presumes that such linkages will be
designed into the interworking unit that connects the DECT access network to whatever mobility-enabled fixed
network is involved. By keeping the entities separate, the handset is capable of responding to any combination of
entity traffic, and this creates great flexibility in fixed network design without breaking full interoperability.
DECT GAP is an interoperability profile for DECT. The intent is that two different products from different
manufacturers that both conform not only to the DECT standard, but also to the GAP profile defined within the DECT
standard, are able to interoperate for basic calling. The DECT standard includes full testing suites for GAP, and GAP
products on the market from different manufacturers are in practice interoperable for the basic functions.
Security
The DECT media access control layer also provides encryption services with the DECT Standard Cipher (DSC). The
encryption is fairly weak, using a 35-bit initialization vector and encrypting the voice stream with 64-bit encryption.
The security algorithm has been broken. Another attack involves impersonating a DECT base station, which allows
calls to be listened to, recorded, and re-routed to a different destination.
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International Mobile Telecommunications (IMT)
IMT 2000, also known as International Mobile Telecommunications 2000, is the ITU globally coordinated
definition of 3G covering key issues such as frequency spectrum use and technical standards.
Different types of 3G Networks specified by IMT 2000
ITU Recommendation ITU-R M.1457 specifies five types of 3G radio interfaces:
IMT-2000 CDMA Direct Spread, also known as UTRA FDD including WCDMA in Japan,
ARIB / DoCoMo recommendation. UMTS is developed by 3GPP.
IMT-2000 CDMA Multi-carrier, also known as Cdma2000 (3X) developed by 3GPP2. IMT-
2000 CDMA2000 includes 1X components, like cdma2000 1X EV-DO.
IMT-2000 CDMA TDD, also known as UTRA TDD and TD-SCDMA. TD-SCDMA is
developed in China and supported by TD-SCDMA Forum.
IMT-2000 TDMA Single Carrier, also known as UWC-136 (Edge) supported by UWCC.
IMT-2000 DECT supported by DECT Forum.
Features
Data rates
ITU has not provided a clear definition of the data rate users can expect from 3G equipment or providers.
Thus users sold 3G service may not be able to point to a standard and say that the rates it specifies are not
being met. While stating in commentary that "it is expected that IMT-2000 will provide higher transmission
rates: a minimum data rate of 2 Mbit/s for stationary or walking users, and 384 kbit/s in a moving vehicle,
the ITU does not actually clearly specify minimum or average rates or what modes of the interfaces qualify
as 3G, so various rates are sold as 3G intended to meet customers expectations of broadband data.
Security
3G networks offer greater security than their 2G predecessors. By allowing the UE (User Equipment) to
authenticate the network it is attaching to, the user can be sure the network is the intended one and not an
impersonator. 3G networks use the KASUMI block cipher instead of the older A5/1 stream cipher.
However, a number of serious weaknesses in the KASUMI cipher have been identified.
In addition to the 3G network infrastructure security, end-to-end security is offered when application
frameworks such as IMS are accessed, although this is not strictly a 3G property.
Applications of 3G
The bandwidth and location information available to 3G devices gives rise to applications not previously
available to mobile phone users. Some of the applications are:
Mobile TV
Video on demand
Video Conferencing
Telemedicine
Location-based services
Global Positioning System (GPS)
12
SATELLITE NETWORKS
History of satellite communication
1945 Arthur C. Clarke publishes an essay about „Extra
Terrestrial Relays“
1957 first satellite SPUTNIK
1960 first reflecting communication satellite ECHO
1963 first geostationary satellite SYNCOM
1965 first commercial geostationary satellite Satellit „Early Bird“
(INTELSAT I): 240 duplex telephone channels or 1 TV
channel, 1.5 years lifetime
1976 three MARISAT satellites for maritime communication
1982 first mobile satellite telephone system INMARSAT-A
1988 first satellite system for mobile phones and data
communication INMARSAT-C
1993 first digital satellite telephone system
1998 global satellite systems for small mobile phones
Applications
� Traditionally
� weather satellites
� radio and TV broadcast satellites
� military satellites
� satellites for navigation and localization (e.g., GPS)
� Telecommunication
� global telephone connections
� backbone for global networks
� connections for communication in remote places or underdeveloped areas
� global mobile communication
� satellite systems to extend cellular phone systems (e.g., GSM orAMPS)
Classical satellite systems
Basics
Satellites in circular orbits
� attractive force Fg = m g (R/r)²
� centrifugal force Fc = m r ω²
� m: mass of the satellite
� R: radius of the earth (R = 6370 km)
� r: distance to the center of the earth
� g: acceleration of gravity (g = 9.81 m/s²)
� ω: angular velocity (ω = 2 π f, f: rotation frequency)
13
Stable orbit
Fg = Fc
Basics
o Elliptical or circular orbits
o Complete rotation time depends on distance satellite-earth
o Inclination: angle between orbit and equator
o Elevation: angle between satellite and horizon
o LOS (Line of Sight) to the satellite necessary for connection
1. High elevation needed, less absorption due to e.g. buildings
o Uplink: connection base station - satellite
o Downlink: connection satellite - base station
o Typically separated frequencies for uplink and downlink
1. Transponder used for sending/receiving and shifting of frequencies
2. Transparent transponder: only shift of frequencies
3. Regenerative transponder: additionally signal regeneration
IElevation
Link budget of satellites
Parameters like attenuation or received power determined by four parameters:
Sending power
Gain of sending antenna
Distance between sender and receiver
Gain of receiving antenna Problems
Varying strength of received signal due to multipath propagation
Interruptions due to shadowing of signal (no LOS) possible solutions
Link Margin to eliminate variations in signal strength
Satellite diversity (usage of several visible satellites at the same time) helps to use less sending power
14
L: Loss
f: carrier frequency
r: distance
c: speed of light
ORBITS
Four different types of satellite orbits can be identified depending on the shape and diameter of the orbit:
� GEO: geostationary orbit, ca. 36000 km above earth surface
� LEO (Low Earth Orbit): ca. 500 - 1500 km
� MEO (Medium Earth Orbit) or ICO (Intermediate Circular Orbit):
ca. 6000 - 20000 km
� HEO (Highly Elliptical Orbit) elliptical orbits
Geostationary satellites
Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°)
Complete rotation exactly one day, satellite is synchronous to earth rotation
Fix antenna positions, no adjusting necessary
Satellites typically have a large footprint (up to 34% of earth surface!), therefore difficult to reuse frequencies
Bad elevations in areas with latitude above 60° due to fixed position above the equator
High transmit power needed
High latency due to long distance (ca. 275 ms)
Not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV
transmission
LEO systems
Orbit ca. 500 - 1500 km above earth surface
Visibility of a satellite ca. 10 - 40 minutes
Global radio coverage possible
Latency comparable with terrestrial long distance
Connections, ca. 5 - 10 ms
Smaller footprints, better frequency reuse
But now handover necessary from one satellite to another
Many satellites necessary for global coverage
More complex systems due to moving satellites
Examples:
Iridium (start 1998, 66 satellites)
Global star (start 1999, 48 satellites)
15
MEO systems
Orbit ca. 5000 - 12000 km above earth surface
Comparison with LEO systems:
Slower moving satellites
Less satellites needed
Simpler system design
For many connections no hand-over needed
Higher latency, ca. 70 - 80 ms
Higher sending power needed
Special antennas for small footprints needed
Example:
ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000
Routing
One solution: inter satellite links (ISL)
Reduced number of gateways needed
Forward connections or data packets within the satellite network as long as possible
Only one uplink and one downlink per direction needed for the connection of two mobile phones
Problems:
More complex focusing of antennas between satellites
High system complexity due to moving routers
Higher fuel consumption
Thus shorter lifetime
Iridium and Teledesic planned with ISL
Other systems use gateways and additionally terrestrial networks
Localization of mobile stations
Mechanisms similar to GSM
Gateways maintain registers with user data
HLR (Home Location Register): static user data
VLR (Visitor Location Register): (last known) location of the mobile station
SUMR (Satellite User Mapping Register):
Satellite assigned to a mobile station
Positions of all satellites
Registration of mobile stations
Localization of the mobile station via the satellite’s position
Requesting user data from HLR
Updating VLR and SUMR
Calling a mobile station
Localization using HLR/VLR similar to GSM
Connection setup using the appropriate satellite
Handover in satellite systems
Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks
caused by the movement of the satellites
Intra satellite handover
Handover from one spot beam to another
Mobile station still in the footprint of the satellite, but in another cell
Inter satellite handover
Handover from one satellite to another satellite
Mobile station leaves the footprint of one satellite
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Gateway handover
Handover from one gateway to another
Mobile station still in the footprint of a satellite, but gateway leaves the footprint
Inter system handover
Handover from the satellite network to a terrestrial cellular network
Mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.
Overview of LEO/MEO systems
FDMA - Frequency Division Multiple Access
Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a
channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. It
is particularly commonplace in satellite communication. FDMA, like other Multiple Access systems, coordinates
access between multiple users. Alternatives include TDMA, CDMA, or SDMA. These protocols are utilized
differently, at different levels of the theoretical OSI model.
Disadvantage: Crosstalk may cause interference among frequencies and disrupt the transmission.
Features
In FDMA all users share the satellite simultaneously but each user transmits at single frequency.
FDMA can be used with both analog and digital signal.
FDMA requires high-performing filters in the radio hardware, in contrast to TDMA and CDMA.
FDMA is not vulnerable to the timing problems that TDMA has. Since a predetermined frequency
band is available for the entire period of communication, stream data (a continuous flow of data that
may not be packetized) can easily be used with FDMA.
Due to the frequency filtering, FDMA is not sensitive to near-far problem which is pronounced for
CDMA.
Each user transmits and receives at different frequencies as each user gets a unique frequency slot
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FDMA is distinct from frequency division duplexing (FDD). While FDMA allows multiple users simultaneous access
to a transmission system, FDD refers to how the radio channel is shared between the uplink and downlink (for
instance, the traffic going back and forth between a mobile-phone and a mobile phone base station). Frequency-
division multiplexing (FDM) is also distinct from FDMA. FDM is a physical layer technique that combines and
transmits low-bandwidth channels through a high-bandwidth channel. FDMA, on the other hand, is an access method
in the data link layer.
FDMA also supports demand assignment in addition to fixed assignment. Demand assignment allows all users
apparently continuous access of the radio spectrum by assigning carrier frequencies on a temporary basis using a
statistical assignment process. The first FDMA demand-assignment system for satellite was developed by COMSAT
for use on the Intelsat series IVA and V satellites.
There are two main techniques:
Multi-channel per-carrier (MCPC)
Single-channel per-carrier (SCPC)
Hints
Satellite frequency is already broken into bands, and is broken in to smaller channels in
Frequency Division Multiple Access (FDMA).
Overall bandwidth within a frequency band is increased due to frequency reuse (a frequency is
used by two carriers with orthogonal polarization).
The number of sub-channels is limited by three factors:
o Thermal noise (too weak a signal will be effected by background noise).
o Intermodulation noise (too strong a signal will cause noise).
o Crosstalk (cause by excessive frequency reusing).
FDMA can be performed in two ways:
o Fixed-assignment multiple access (FAMA): The sub-channel assignments are of a
fixed allotment. Ideal for broadcast satellite communication.
o Demand-assignment multiple access (DAMA): The sub-channel allotment changes
based on demand. Ideal for point to point communication.
DAMA - Demand Assigned Multiple Access
Demand Assigned Multiple Access (DAMA) is a technology used to assign a channel to clients that don't
need to use it constantly. DAMA systems assign communication channels based on requests issued from
user terminals to a network control system. When the circuit is no longer in use, the channels are then
returned to the central pool for reassignment to other users.
Channels are typically a pair of carrier frequencies (one for transmit and one for receive), but can be other
fixed bandwidth resources such as timeslots in a TDMA burst plan or even physical party line channels.
Once a channel is allocated to a given pair of nodes, it is not available to other users in the network until
their session is finished.
It allows utilizing of one channel (radio or baseband frequency, timeslot, etc.) by many users sequentially at
different times. This technology is mainly useful with sparsely used networks of transient clients, as opposed
to PAMA (Permanently Assigned Multiple Access). By using DAMA technology the number of separate
nodes that can use a limited pool of circuits can be greatly increased at the expense of no longer being able
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to provide simultaneous access for all possible pairs of nodes. A five-channel DAMA network can only
have five simultaneous conversations but could have any number of nodes. A five-channel PAMA network
permanently supports five simultaneous conversations, with channel ownership remaining with their
permanently assigned nodes even when idle.
DAMA and PAMA are related only to channel/resource allocation and should not be confused with the
Multiple access/multiplexing methods (such as FDMA frequencies, TDMA slots, CDMA codes, or others)
intended to divide a single communication channel into multiple virtual channels. These systems typically
use resource allocation protocols that allow a more rapid (although often less deterministic, consider CDMA
collisions) near-real-time allocation of bandwidth based on demand and data priority. However, in sparsely
allocated multiple-access channels, DAMA can be used to allocate the individual virtual channel resources
provided by the multiple-access channel. This is most common in environments that are sufficiently
sparsely utilized that there is no need to add complexity just to recover "conversation gap" idle periods.
DAMA is widely used in satellite communications, especially in VSAT systems. It is very effective in
environments comprising multiple users each having a low to moderate usage profile.
DAMA is often used in military environments due to the relative simplicity of implementation, ease of
modeling, and the fact that military usage profiles are a very good fit. In military SATCOM, it has the added
advantage that it can function in a bent pipe environment, thus requires no special security or coordination
hardware on the satellite. This allows the master and slave ground stations to be upgraded repeatedly to
change or improve security and compression without requiring an expensive satellite replacement.
DAMA
Channel efficiency only 18% for Aloha, 36% for Slotted Aloha (assuming Poisson distribution for packet
arrival and packet length)
Reservation can increase efficiency to 80%
a sender reserves a future time-slot
sending within this reserved time-slot is possible without collision
reservation also causes higher delays
typical scheme for satellite links
Examples for reservation algorithms:
Explicit Reservation according to Roberts (Reservation-ALOHA)
Implicit Reservation (PRMA)
Reservation-TDMA
Access method DAMA: Explicit Reservation
Explicit Reservation (Reservation Aloha): Two modes:
ALOHA mode for reservation:
Competition for small reservation slots, collisions possible
reserved mode for data transmission in reserved slots (no collisions possible)
Important for all stations to keep the reservation list consistent. Thus all stations have to
synchronize periodically
19
Broadcasting Systems
Digital Audio Broadcasting
Digital Audio Broadcasting (DAB) is a digital radio technology for broadcasting radio stations, used in several
countries, particularly in Europe. As of 2006, approximately 1,002 stations worldwide broadcast in the DAB format.
The DAB standard was initiated as a European research project in the 1980s. The Norwegian Broadcasting
Corporation (NRK) launched the very first DAB channel in the world on June 1 1995 (NRK Klassisk), and the BBC
and SR launched their first DAB digital radio broadcasts in September 1995. DAB receivers have been available in
many countries since the end of the nineties. DAB may offer more radio programmes over a specific spectrum than
analogue FM radio. DAB is more robust with regard to noise and multipath fading for mobile listening, since DAB
reception quality first degrades rapidly when the signal strength falls below a critical threshold, whereas FM reception
quality degrades slowly with the decreasing signal.
An unblinded "informal listening test" by Sverre Holm has shown that for stationary listening the audio quality on
DAB is subjectively lower than FM stereo (but this may be due to observer bias). Most stations using a bit rate of 128
kbit/s or less, with the MP2 audio codec, which requires 160 kbit/s to achieve perceived FM quality. 128 kbit/s gives
better dynamic range or signal-to-noise ratio than FM radio, but a more smeared stereo image, and an upper cutoff
frequency of 14 kHz, corresponding to 15 kHz of FM radio.[5]
However, "CD sound quality" with MP2 is possible
"with 256..192 kbps".
An upgraded version of the system was released in February 2007, which is called DAB+. DAB is not forward
compatible with DAB+, which means that DAB-only receivers will not be able to receive DAB+ broadcasts.[7]
DAB+
is approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec, and DAB+ can provide
high quality audio with as low as 64 kbit/s. Reception quality will also be more robust on DAB+ than on DAB due to
the addition of Reed-Solomon error correction coding.
In spectrum management, the bands that are allocated for public DAB services, are abbreviated with T-DAB, where
the "T" stands for terrestrial.
More than 20 countries provide DAB transmissions, and several countries, such as Australia, Italy, Malta, Switzerland
and Germany, have started transmitting DAB+ stations. See Countries using DAB/DMB. However, DAB radio has
still not replaced the old FM system in popularity.
Benefits of DAB
Current AM and FM terrestrial broadcast technology is well established, compatible, and cheap to manufacture.
Benefits of DAB over analogue systems are explained below.
Improved features for users
DAB radios automatically tune to all the available stations, offering a list for the user to select from.
DAB can carry "radiotext" (in DAB terminology, Dynamic Label Segment, or DLS) from the station giving real-time
information such as song titles, music type and news or traffic updates. Advance programme guides can also be
transmitted. A similar feature also exists on FM in the form of the RDS. (However, not all FM receivers allow radio
stations to be stored by name.)
DAB receivers can display time of day as encoded into transmissions, so is automatically corrected when travelling
between time zones and when changing to or from Daylight Saving. This is not implemented on all receivers, and
some display time only when in "Standby" mode.
20
Some radios offer a pause facility on live broadcasts, caching the broadcast stream on local flash memory, although
this function is limited.
More stations
DAB is not more bandwidth efficient than analogue measured in programmes per MHz of a specific transmitter (the
so called link spectral efficiency). However, it is less susceptible to co-channel interference (cross talk), which makes
it possible to reduce the reuse distance, i.e. use the same radio frequency channel more densely. The system spectral
efficiency (the average number of radio programmes per MHz and transmitter) is a factor three more efficient than
analog FM for local radio stations, as can be seen in the above numerical example. For national and regional radio
networks, the efficiency is improved by more than an order of magnitude due to the use of SFNs. In that case,
adjacent transmitters use the same frequency.
In certain areas — particularly rural areas — the introduction of DAB gives radio listeners a greater choice of radio
stations. For instance, in South Norway, radio listeners experienced an increase in available stations from 6 to 21
when DAB was introduced in November 2006.
Reception quality
The DAB standard integrates features to reduce the negative consequences of multipath fading and signal noise,
which afflict existing analogue systems.
Also, as DAB transmits digital audio, there is no hiss with a weak signal, which can happen on FM. However, radios
in the fringe of a DAB signal, can experience a "bubbling mud" sound interrupting the audio and/or the audio cutting
out altogether.
Due to sensitivity to doppler shift in combination with multipath propagation, DAB reception range (but not audio
quality) is reduced when traveling speeds of more than 120 to 200 km/h, depending on carrier frequency.
Less pirate interference
The specialised nature and cost of DAB broadcasting equipment provide barriers to pirate radio stations broadcasting
on DAB. In cities such as London with large numbers of pirate radio stations broadcasting on FM, this means that
some stations can be reliably received via DAB in areas where they are regularly difficult or impossible to receive on
FM due to pirate radio interference.
Variable bandwidth
Mono talk radio, news and weather channels and other non-music programs need significantly less bandwidth than a
typical music radio station, which allows DAB to carry these programmes at lower bit rates, leaving more bandwidth
to be used for other programs.
However, this had led to the situation where some stations are being broadcast in mono
Transmission costs
It is common belief that DAB is more expensive to transmit than FM. It is true that DAB uses higher frequencies than
FM and therefore there is a need to compensate with more transmitters, higher radiated powers, or a combination, to
achieve the same coverage. A DAB network is also more expensive than an FM network. However, the last couple of
years have seen significant improvement in power efficiency for DAB-transmitters.
This efficiency originates from the ability a DAB network has in broadcasting more channels per network. One
network can broadcast 6-10 channels (with MPEG audio codec) or 10-16 channels (with HE AAC codec). Hence, it is
21
thought that the replacement of FM-radios and FM-transmitters with new DAB-radios and DAB-transmitters will not
cost any more as opposed to newer FM facilities.
Cheaper transmission costs is backed by independent network studies from Teracom (Sweden) and SSR/SRG
(Switzerland). Among other things they show that DAB is up to 6 times less expensive than FM.
Disadvantages of DAB
Reception quality
The reception quality on DAB can be poor even for people that live well within the coverage area. The reason for this
is that the old version of DAB uses weak error correction coding, so that when there are a lot of errors with the
received data not enough of the errors can be corrected and a "bubbling mud" sound occurs. In some cases a complete
loss of signal can happen. This situation will be improved upon in the new DAB standard (DAB+, discussed below)
that uses stronger error correction coding and as additional transmitters are built.
Audio Quality
Broadcasters have been criticized for ‘squeezing in’ more stations per ensemble than recommended, by:
Minimizing the bit-rate, to the lowest level of sound-quality that listeners are willing to tolerate, such as 128
kbit/s for stereo and even 64 kbit/s for mono speech radio.
Having few digital channels broadcasting in stereo.
Signal delay
The nature of a SFN is such that the transmitters in a network must broadcast the same signal at the same time. To
achieve synchronization, the broadcaster must counter any differences in propagation time incurred by the different
methods and distances involved in carrying the signal from the multiplexer to the different transmitters. This is done
by applying a delay to the incoming signal at the transmitter based on a timestamp generated at the multiplexer,
created taking into account the maximum likely propagation time, with a generous added margin for safety. Delays in
the receiver due to digital processing (e.g. deinterleaving) add to the overall delay perceived by the listener.[19]
The
signal is delayed by 2–4 seconds depending on the decoding circuitry used. This has disadvantages:
DAB radios are out of step with live events, so the experience of listening to live commentaries on events
being watched is impaired;
Delayed time signals : Even in a well-defined network with a fixed delay, the listener has to apply an offset
when using the broadcast time signal to set a clock.
Listeners using a combination of analog (AM or FM) and DAB radios (e.g. in different rooms of a house) will
hear a confusing mixture when both receivers are within earshot.
Coverage
As DAB is at a relatively early stage of deployment, DAB coverage is poor in nearly all countries in comparison to
the high population coverage provided by FM.
Compatibility
In 2006 tests began using the much improved HE-AAC codec for DAB+. Virtually none of the receivers made before
2008 support the new codec, however, thus making them partially obsolete once DAB+ broadcasts begin and
completely obsolete once the old MPEG-1 Layer 2 stations are switched off. However new receivers are both DAB
and DAB+ compatible.
22
Power requirements
As DAB requires digital signal processing techniques to convert from the received digitally encoded signal to the
analogue audio content, the complexity of the electronic circuitry required to do this is high. This translates into
needing more power to effect this conversion than compared to an analogue FM to audio conversion, meaning that
portable receiving equipment will tend to have a shorter battery life, or require higher power (and hence more bulk).
This means that they use more energy than analogue Band II VHF receivers.
As an indicator of this increased power consumption, some radio manufacturers quote the length of time their
receivers can play on a single charge. For a commonly used FM/DAB-receiver from manufacturer PURE, this is
stated as: DAB 10 hours, FM 22 hours.
Use of Licensed Codec
The use of MPEG and latterly AAC has prompted criticism of the fact that a (large) public system is financially
supporting a private company. In general, an open system will permit equipment to be bought from various sources in
competition with each other but by selecting a single vendor of codec, with which all equipment must be compatible,
this is not possible.
Digital Video Broadcasting
Digital Video Broadcasting (DVB) is a suite of internationally accepted open standards for digital television. DVB
standards are maintained by the DVB Project, an international industry consortium with more than 270 members, and
they are published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute
(ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union
(EBU). Many aspects of DVB are patented, including elements of the MPEG video coding and audio coding.
Transmission
DVB systems distribute data using a variety of approaches, including:
Satellite: DVB-S, DVB-S2 and DVB-SH
o DVB-SMATV for distribution via SMATV
Cable: DVB-C, DVB-C2
Terrestrial television: DVB-T, DVB-T2
o Digital terrestrial television for handhelds: DVB-H, DVB-SH
Microwave: using DTT (DVB-MT), the MMDS (DVB-MC), and/or MVDS standards (DVB-MS)
These standards define the physical layer and data link layer of the distribution system. Devices interact with the
physical layer via a synchronous parallel interface (SPI), synchronous serial interface (SSI), or asynchronous serial
interface (ASI). All data is transmitted in MPEG transport streams with some additional constraints (DVB-MPEG).
DVB has established a 3D TV group (CM-3DTV) to identify "what kind of 3D-TV solution does the market want and
need, and how can DVB play an active part in the creation of that solution?" The CM-3DTV group held a DVB 3D-
TV Kick-off Workshop in Geneva on January 25, 2010, followed by the first CM-3DTV meeting the next day.[3]
DVB
now defines a new standard for 3D video broadcast: DVB 3D-TV.
Content
Besides digital audio and digital video transmission, DVB also defines data connections (DVB-DATA - EN 301 192)
with return channels (DVB-RC) for several media (DECT, GSM, PSTN/ISDN, satellite etc.) and protocols (DVB-
IPTV: Internet Protocol; DVB-NPI: network protocol independent).
23
Older technologies such as teletext (DVB-TXT) and vertical blanking interval data (DVB-VBI) are also supported by
the standards to ease conversion. However, for many applications more advanced alternatives like DVB-SUB for
subtitling are available.
Encryption and metadata
The conditional access system (DVB-CA) defines a Common Scrambling Algorithm (DVB-CSA) and a physical
Common Interface (DVB-CI) for accessing scrambled content. DVB-CA providers develop their wholly proprietary
conditional access systems with reference to these specifications. Multiple simultaneous CA systems can be assigned
to a scrambled DVB program stream providing operational and commercial flexibility for the service provider.
DVB is also developing a Content Protection and Copy Management system for protecting content after it has been
received (DVB-CPCM), which is intended to allow flexible use of recorded content on a home network or beyond,
while preventing unconstrained sharing on the Internet. DVB-CPCM has been the source of much controversy in the
popular press and It is said that CPCM is the DVB's answer to the failed American Broadcast Flag.
DVB transports include metadata called Service Information (DVB-SI, ETSI EN 300 468, ETSI TR 101 211) that
links the various elementary streams into coherent programs and provides human-readable descriptions for electronic
program guides as well as for automatic searching and filtering.
Recently, DVB has adopted a profile of the metadata defined by the TV-Anytime Forum (DVB-TVA, ETSI TS
102323). This is an XML Schema based technology and the DVB profile is tailored for enhanced Personal Digital
Recorders. DVB lately also started an activity to develop a service for IPTV (DVB-IPI, ETSI TR 102033, ETSI TS
102034, ETSI TS 102814) which also includes metadata definitions for a broadband content guide (DVB-BCG, ETSI
TS 102 539).
Software platform
The DVB Multimedia Home Platform (DVB-MHP) defines a Java-based platform for the development of consumer
video system applications. In addition to providing abstractions for many DVB and MPEG-2 concepts, it provides
interfaces for other features like network card control, application download, and layered graphics.
Return channel
DVB has standardized a number of return channels that work together with DVB(-S/T/C) to create bi-directional
communication. RCS is short for Return Channel Satellite, and specifies return channels in C, Ku and Ka frequency
bands with return bandwidth of up to 2 Mbit/s. DVB-RCT is short for Return Channel Terrestrial, specified by ETSI
EN 301958.
Adoption
DVB-S and DVB-C were ratified in 1994. DVB-T was ratified in early 1997. The first commercial DVB-T broadcasts
were performed by the United Kingdom's Digital TV Group in late 1998. In 2003 Berlin, Germany was the first area
to completely stop broadcasting analog TV signals. Most European countries are fully covered by digital television
and many have switched off PAL/SECAM services.
In Europe, as well as in Australia, South Africa and India, DVB is used throughout. This also holds true for cable and
satellite in most Asian, African and many South American countries. Many of these have not yet selected a format for
digital terrestrial broadcasts (DTTV) and a few (Canada, El Salvador, Honduras, Mexico, South Korea and the United
States) have chosen ATSC instead of DVB-T.
UNIT II TELECOMMUNICATION SYSTEMS
Part A
1) What are the four types of handover available in GSM?
1. Intra cell Handover
2. Inter cell Intra BSC Handover
3. Inter BSC Intra MSC handover
4. Inter MSC Handover
2) What are the categories of Mobile services?
• Bearer services
• Tele services
• Supplementary services
3) What are the services provided by supplementary services?
• User identification
• Call redirection
• Call forwarding
• Closed user groups
• Multiparty Communication
4) What are types of Handover?
Intra-cell handover
Inter-cell, intra- BSC handover
Inter-BSC, intra-MSC handover
Inter MSC handover
5) What is meant by GPRS?
The General Packet Radio Service provides packet mode transfer for applications
that exhibit traffic patterns such as frequent transmission of small volumes.
6) What are subsystems in GSM system?
• Radio subsystem (RSS)
• Network & Switching subsystem (NSS)
• Operation subsystem (OSS)
7) What is the information in SIM?
• Card type, serial no, list of subscribed services
• Personal Identity Number (PIN)
• Pin Unlocking Key (PUK)
• An Authentication Key (KI)
8) Define Normal Burst?
The frame used for normal data transmission within a time slot is called Normal Burst.
9) What are the logical channels in GSM?
• Traffic channel(TCH) • Control channel(CCH)
10) What is the function of Medium Access Control Layer?
The functions of Medium Access Control Layer is responsible for establishes,
maintains, and releases channels for higher layers by activating and deactivating physical
channels.
11) What is Handover?
The satellite is the base station in satellite communication systems and that itself is moving. So,
additional instance of handover are necessary due to the movement of the satellite
1. Intra Satellite handover:
2. Inter Satellite handover.
3. Gateway handover.
4. Inter System handover.
12) What is MSC?
Main Service Channel (MSC) carries all user data.
eg. audio, multimedia data.
13) What is FIC?
The Fast Information Channel (FIC) contains Fast Information Block (FIB) with 256bits each(16
bit checksum). An FIC carries all control information which is required for interpreting the
configuration and content of the MSC.
14) What are the different types of disk?
• A flat disks
• Skewed disks
• Multi disks
15) What are the goals of DVB?
The goal of DVB is to introduce digital TV broadcasting using satellite transmission (DVB-5)
cable technology (DVB-c) and terrestrial transmission (DVB-7).
16) Name some of the formats supported by MOT?
• Multimedia and Hypermedia information coding experts group (MHEG)
• Join photograph’s experts group (JPEG)
• American standard code for information interchange (ASCII)
• Moving pictures expert group (MPEG)
• Hypertext markup language (HTML)
• Hypertext transfer protocol (HTTP)
• Bitmap (BMP)
• Graphics interchange format (GIF)
17) Give structure MOT object.
7bytes
variable size
variable size
Header core
Header Extension Body
Header core: contain the size of the header and body and the content type of the object.
Header Extension: contains additional object handling data such as repetition distance to support
caching, segmentation information and priority of the data.
Body: contains arbitrary data to be transmitted.
18) What are different interleaving and repetition schemes applied by DAB to objects and
segments?
1. Object Repetition.
2. Interleaved Objects.
3. Segment repetition.
4. Header repetition.
19) What are the advantages of DAB?
1. DAB can offer sound in CD like quality.
2. DAB can use single frequency network where all senders transmitting the same radio program
can operate at the same frequency.
3. DAB use VHF and UHF frequency bands.
4. DAB uses DQPSK modulation scheme.
5. DAB user COFDM and FEC.
6. DAB can transmit up to six stereo audio programmes with a data rate of 192kbit/s each.
20) What is object repetition?
DAB can repeat objects several times. If an object A consists of four segments (A1,A2,A3,A4) a
single repetition pattern would be A1A2A3A4A1A2A3A4A1A2A3A4……..
21) What is EIT?
Event Information Table (EIT) contains status information about the current transmission and
some additional information for set-top boxes.
22) What is the service information sent by DVB?
Digital Video Broadcast Containers are basically MPEG-2 frames. DVB sends service
information. This information is,
1. Network information table (NIT).
2. Service Description Table (SDT).
3. Event Information Table (EIT).
4. Time and Date Table (TDT)
23) What are the advantages of DVB?
1. Data rates planned for users are 6-38mbit/s for the downlink and 33-100kbit/s for the uplink.
2. Transmitted along with TV programmes and doesn’t require additional lines or hardware per
customer.
3. Can be used in remote areas and developing countries where there is no high bandwidth wired
network.
24) What is meant by beacon?
A beacon contains a timestamp and other management information used for power management
and roaming.
e.g., identification of the base station subsystem (BSS)
25) What is Active scanning?
Active scanning comprises sending a probe on each channel and waiting for response. Beacon
and Probe response contain the information necessary to join the new BSS.
26) What is Passive Scanning?
Passive Scanning Simply means listening into the medium to find other networks, i.e. receiving
the beacon of another network issued by the synchronization function within an access point.
UNIT2 TELECOMMUNICATION SYSTEMS
Part B
1. Write notes on DECT and TETRA
System architecture, Protocol Architecture
2. Write notes on UMTS and IMT – 2000
UMTS basic architecture, UTRA FDD mode, UTRA TDD mode
3. Explain broadcast systems in detail.
Overview – Cyclical repetition of data – Digital audio broadcasting – Multimedia object transfer
protocol – Digital video broadcasting.
4. Explain satellite systems in detail.
History – Applications – Basics – GEO – LEO – MEO – Routing – Localization – Handover –
Examples.
5. Explain GSM systems in detail.
Mobile services- System Architecture – Radio interface – Protocols –
Localization and calling – Handover – Security - New data services –
6. Explain GPRS systems in detail.
System architecture, Protocol Architecture– Handover – Security.\
7. Explain DAB in detail.
Media access
Frequencies
second phase: one out of 9 frequency blocks in the L-band
Date-rates:
Modulation:
Digital services:
8. Explain DVB in detail.
Container
High-speed Internet
9. Explain the following a) Routing b) Hand over c) Localization
10. Explain the various satellite orbit and the parameters associated.
Parameters of satellites and explanations-Three orbits and explanation
1
UNIT III
WIRLESS LAN
Wireless LAN – IEEE 802.11 - Architecture – services – MAC – Physical layer – IEEE 802.11a -
802.11b standards – HIPERLAN – Blue Tooth.
WIRELESS LAN
Characteristics of wireless LANs
Advantages
o Very flexible within the reception area
o Ad-hoc networks without previous planning possible
o (almost) no wiring difficulties (e.g. historic buildings, firewalls)
o More robust against disasters like, e.g., earthquakes, fire - or users pulling a plug...
Disadvantages
o Typically very low bandwidth compared to wired networks (1-10 Mbit/s)
o Many proprietary solutions, especially for higher bit-rates, standards take their time
(e.g. IEEE 802.11)
o Products have to follow many national restrictions if working wireless, it takes a vary
long time to establish global solutions like, e.g., IMT-2000
Design goals for wireless LANs
o global, seamless operation
o low power for battery use
o no special permissions or licenses needed to use the LAN
o robust transmission technology
o simplified spontaneous cooperation at meetings
o easy to use for everyone, simple management
o protection of investment in wired networks
o security (no one should be able to read my data), privacy (no one should be able to collect user
profiles), safety (low radiation)
o transparency concerning applications and higher layer protocols, but also location awareness if
necessary
Comparison: infrared vs. radio transmission
2
Comparison: infrastructure vs. ad-hoc networks
IEEE 802.11 - ARCHITECTURE – SERVICES - ARCHITECTURE – SERVICES – MAC – PHYSICAL LAYER – IEEE 802.11A - 802.11B STANDARDS
802.11 - Architecture of an infrastructure network
Station (STA)
o terminal with access mechanisms to the wireless medium and radio contact to the
access point
Basic Service Set (BSS)
o group of stations using the same radio frequency
Access Point
o station integrated into the wireless LAN and the distribution system
Portal
o bridge to other (wired) networks
Distribution System
o interconnection network to form one logical network (EES: Extended Service Set)
based
on several BSS
3
802.11 - Architecture of an ad-hoc network
Direct communication within a limited range
o Station (STA):
terminal with access mechanisms to the wireless medium
o Basic Service Set (BSS):
group of stations using the same radio frequency
IEEE standard 802.11
802.11 - Layers and functions
MAC -Access mechanisms, fragmentation, encryption
MAC Management - Synchronization, roaming, MIB, power management
PLCP Physical Layer Convergence Protocol - Clear channel assessment signal (carrier sense)
PMD Physical Medium Dependent - Modulation, coding
PHY Management - Channel selection, MIB
Station Management - Coordination of all management functions
4
802.11 - Layers
802.11 - Physical layer
3 versions: 2 radio (typ. 2.4 GHz), 1 IR
o data rates 1 or 2 Mbit/s
FHSS (Frequency Hopping Spread Spectrum)
o spreading, despreading, signal strength, typ. 1 Mbit/s
o min. 2.5 frequency hops/s (USA), two-level GFSK modulation
DSSS (Direct Sequence Spread Spectrum)
o DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK
for 2 Mbit/s (Differential Quadrature PSK)
o preamble and header of a frame is always transmitted with 1 Mbit/s, rest of
transmission 1 or 2 Mbit/s
o chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)
o max. radiated power 1 W (USA), 100 mW (EU), min. 1mW
Infrared
o 850-950 nm, diffuse light, typ. 10 m range
o carrier detection, energy detection, synchronization
802.11 - MAC layer I - DFWMAC
Traffic services
Asynchronous Data Service (mandatory)
exchange of data packets based on “best-effort”
support of broadcast and multicast
Time-Bounded Service (optional)
implemented using PCF (Point Coordination Function)
Access methods
DFWMAC-DCF CSMA/CA (mandatory)
collision avoidance via randomized „back-off“ mechanism
minimum distance between consecutive packets
ACK packet for acknowledgements (not for broadcasts)
DFWMAC-DCF w/ RTS/CTS (optional)
Distributed Foundation Wireless MAC
avoids hidden terminal problem
DFWMAC- PCF (optional)
access point polls terminals according to a list
5
Priorities
defined through different inter frame spaces
no guaranteed, hard priorities
SIFS (Short Inter Frame Spacing)
highest priority, for ACK, CTS, polling response
PIFS (PCF IFS)
medium priority, for time-bounded service using PCF
DIFS (DCF, Distributed Coordination Function IFS)
lowest priority, for asynchronous data service
802.11 - MAC layer
MAC address format
DS: Distribution System
AP: Access Point
DA: Destination Address
SA: Source Address
BSSID: Basic Service Set Identifier
RA: Receiver Address
TA: Transmitter Address
MAC management
Synchronization
try to find a LAN, try to stay within a LAN
timer etc.
Power management
sleep-mode without missing a message
periodic sleep, frame buffering, traffic measurements
Association/Reassociation
integration into a LAN
roaming, i.e. change networks by changing access points
scanning, i.e. active search for a network
MIB - Management Information Base
managing, read, write
scenario to DS from DS
address 1 address 2 address 3 address 4
ad-hoc network 0 0 DA SA BSSID -
infrastructure network, from AP
0 1 DA BSSID SA -
infrastructure network, to AP
1 0 BSSID SA DA -
infrastructure network, within DS
1 1 RA TA DA SA
6
HIPERLAN
• ETSI standard– European standard, cf. GSM, DECT, ...
– Enhancement of local Networks and interworking with fixed networks
– integration of time-sensitive services from the early beginning
• HIPERLAN family– one standard cannot satisfy all requirements
• range, bandwidth, QoS support
• commercial constraints
– HIPERLAN 1 standardized since 1996
physical layer
channel access
control layer
medium access
control layer
physical layer
data link layer
HIPERLAN layers OSI layers
network layer
7.31.1
higher layers
physical layer
medium access
control layer
logical link
control layer
IEEE 802.x layers
Original HIPERLAN protocol family
HIPERLAN 1 - Characteristics
Data transmission
point-to-point, point-to-multipoint, connectionless
23.5 Mbit/s, 1 W power, 2383 byte max. packet size
Services
asynchronous and time-bounded services with hierarchical priorities
compatible with ISO MAC
Topology
HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4
Application wireless LAN access to ATM fixed networks
wireless local loop
point-to-point wireless ATM connections
Frequency 5.1-5.3GHz 17.2-17.3GHz
Topology decentralized ad-hoc/infrastructure
cellular, centralized
point-to-multipoint
point-to-point
Antenna omni-directional directional
Range 50 m 50-100 m 5000 m 150 m
QoS statistical ATM traffic classes (VBR, CBR, ABR, UBR)
Mobility <10m/s stationary
Interface conventional LAN ATM networks
Data rate 23.5 Mbit/s >20 Mbit/s 155 Mbit/s
Power conservation
yes not necessary
7
infrastructure or ad-hoc networks
transmission range can be larger then coverage of a single node („forwarding“ integrated
in mobile terminals)
Further mechanisms
power saving, encryption, checksums
Services and protocols
CAC service
definition of communication services over a shared medium
specification of access priorities
abstraction of media characteristics
MAC protocol
MAC service, compatible with ISO MAC and ISO MAC bridges
uses HIPERLAN CAC
CAC protocol
provides a CAC service, uses the PHY layer, specifies hierarchical access mechanisms
for one or several channels
Physical protocol
send and receive mechanisms, synchronization, FEC, modulation, signal strength
HIPERLAN 1 - Physical layer
Scope
modulation, demodulation, bit and frame synchronization
forward error correction mechanisms
measurements of signal strength
channel sensing
Channels
3 mandatory and 2 optional channels (with their carrier frequencies)
mandatory
channel 0: 5.1764680 GHz
channel 1: 5.1999974 GHz
channel 2: 5.2235268 GHz
optional (not allowed in all countries)
channel 3: 5.2470562 GHz
channel 4: 5.2705856 GHz
BLUETOOTH
Consortium: Ericsson, Intel, IBM, Nokia, Toshiba - many members
Scenarios
connection of peripheral devices
loudspeaker, joystick, headset
support of ad-hoc networking
small devices, low-cost
bridging of networks
e.g., GSM via mobile phone - Bluetooth - laptop
Simple, cheap, replacement of IrDA, low range, lower data rates
2.4 GHz, FHSS, TDD, CDMA
8
Bluetooth MAC layer
Scatternets
UNIT III WIRELESS NETWORKS
Part A
1) What is the primary goal of IEE 802.11?
The primary goal of the standard was the specification of a simple, robust, WLAN which offers
time bounded and asynchronous services also it should be able to operate with multiple physical
layers.
2) What is meant by SIFS?
SIFS means Short Inter Frame Spacing. The shortest waiting time defined for short control
message such as acknowledgements or polling response.
3) What are Advantages of wireless LAN?
Flexibility, Planning, Design, Robustness, Quality Service, Cost, Proprietary Solution,
Restriction, Safety and Security
4) What are Design Goals of Wireless LAN?
Global Operation
Low Power
License-free Operation
Robust transmission technology
Simplified spontaneous co-operation
Easy to use
Protection of investment
Safety and Security
Transparency for application
5) What are the three Low Power States provided by Bluetooth?
PARK state
HOLD state
SNIFF state
6) What is SCO?
SCO-stands for Synchronous Connection Oriented Link
Standard telephone (voice) connection requires symmetrical, circuit-switched, point-to point
connections. For this type of link, the master reserves two consecutive slots at fixed intervals.
7) What are the three phases in EY-NPMA?
i. Prioritization: Determine the highest priority of a data packet ready to be sent on
competing nodes.
ii. Contention: Eliminate all but one of the contenders, if more than one sender has
the highest current priority.
iii. Transmission: Finally, transmit the packet of the remaining node.
8) What are Advantages and Disadvantages of Infrared?
Advantages:
i. Simple & extremely cheap senders and receivers which integrated in almost all mobile devices
ii. No licenses are needed for infrared technology and shielding is very simple.
iii. Electrical devices do not interfere with infrared transmission.
Disadvantages:
i. Low bandwidth
ii. Quite easily shielded
iii. Cannot Penetrate
9) What are the system integration functions of MAC management?
• Synchronization
• Power management
• Roaming
• Management information base (MIB)
10) What do you meant by roaming?
Moving between access point is called roaming. Even wireless networks may require more than
one access point to cover all rooms. In order to provide uninterrupted service, we require
roaming when the user moves from one access point to another.
11) What is mobile routing?
Even if the location of a terminal is known to the system, it still has to route the traffic through
the network to the access point currently responsible for the wireless terminal.
Each time a user moves to a new access point, the system must reroute traffic. This is known as
mobile routing.
12) What are the functions which support service and connection control?
>Access point control function
>Call control and connection control function
>Network security agent
>Service control function
>Mobility management function
13) What are the examples for service scenarios identified in WATM ?
>Office environments
>Universities, schools, training, centres
>Industry
>Hospitals
>Home
>Networked vehicles
14) What is BRAN?
The broadband radio access networks (BRAN) which have been standardized by
European Telecommunications Standard Institute( ETSI) are a possible choice for an RAL
for WATM. Although BRAN has been standardized independently from WATM, there is
co-operation between the two to concentrate the common efforts on one goal. The main
motivation behind BRAN is the deregulation and privatization of the telecommunication
sector in Europe.
15) What are the different network types of BRAN?
>Hyperlan1
>Hyperlan2
>Hyper access
>Hyperlink
16) What is the main problem for WATM during handover?
The main problem for WATM during the handover is rerouting of all connections and
maintaining connection quality.
17) What are the different segments in ATM end-to-end connection?
An ATM end-to-end connection is separated into different segments.
>A fixed segment is a part of the connection that is not affected by the handover
>Handover segment is affected by the handover and is located completely within a handover
domain.
18) What is anchor point?. The Anchor point is the boundary between a handover segment and a fixed
segment.
19) What are different types of handover?
>Hard handover
>Terminal initiated
>Network initiated
>Network initiated, terminal assisted
>Network controlled
>Backward handover
>Forward handover
20) What is mobile terminal and wireless terminal?.
Mobile terminal is a standard ATM terminal with the additional capability of reconnecting after
access point change. the terminal can be moved between different access point within a certain
domain. Wireless terminal is accessed via a wireless link, but the terminal itself is fixed,
i.e., the terminal keeps its access point to the network.
UNIT3 WIRELESS NETWORKS
Part B
1. Explain IEEE802.11 standard for WLANS in detail.
System architecture – Protocol architecture – Physical layer – Frequency hopping spread
spectrum, Direct spectrum spread spectrum, Infrared – Medium access control layer- Basic
DFWMAC-DCF using CSMA/CA, DFWMAC-DCF with RTS/CTS extension, DFWMAC-PCF
with polling, MC frames – MAC management –Synchronization, Power management, Roaming
– 802.11b.
2 Write notes on WATM services and Functions.
Wireless mobile terminal side functions and mobility supporting network side functions.
3. Write notes on WATM handover.
Handover reference model, handover requirements, types of handover, hand over scenarios,
backward handover, and forward handover.
4. Write notes on location management, addressing and access point control protocol.
Requirements for location management, procedures and entities
5. Give a detail note on HYPERLAN.
Reference model and configurations- Physical layer –Data link control layer – broadcast phase,
downlink phase, uplink phase, random access phasebroascast channel, frame channel, access
feedback channel, long transport channel, short transport channel, random channel –
Convergence layer – Ethernet, IEEE 1394 (Firewire), ATM.
6. Account on BLUETOOTH in detail.
User scenarios- Connection of peripheral devices, support of ad-hoc networking, bridging of
networks – Architecture – networking, protocol stackradio layer – Baseband layer- physical
links- synchronous connection-oriented link, Asynchronous connectionless link – link manager
protocol –L2CAP –Security –SDP – Profiles –IEEE802.15 .
1
UNIT IV
MOBILE NETWORK LAYER
Mobile IP – Dynamic Host Configuration Protocol - Routing – DSDV – DSR – Alternative Metrics
Mobile IP
A standard for mobile computing and networking
Computers doesn’t stay put.
Change location without restart its application or terminating any ongoing communication
IP Networking
Protocol layer
Network Layer
Transport Layer
What does IP do
moving packets from source to destination
No ’end-to-end’ guarantees
IP addresses
Network-prefix
Host portion
IP Routing
Packet Header
Network-prefix
Every node on the same link has the same network-prefix
Mobile IP Solves the following problems
f a node moves from one link to another without chnging its IP address, it will be unable to receive
packets at the new link; and
If a node moves from one link to another without chnging its IP address, it will be unable to receive
packets at the new link; and
Mobile IP Overview
Solution for Internet
Scalable, robust, secure, maintain communication
Use their permanent IP address
Routing protocol
Route packets to nodes that could potentially change location very rapidly
Layer 4-7, outside Mobile IP, but will be of major interest
2
Mobile IP: Terminology
• Mobile Node (MN)
– node that moves across networks without changing its IP address
• Correspondent Node (CN)
– ost with which MN is “corresponding” (TCP)
• Home Agent (HA)
– host in the home network of the MN, typically a router
– registers the location of the MN, tunnels IP packets to the COA
• Foreign Agent (FA)
– host in the current foreign network of the MN, typically a router
– forwards tunneled packets to the MN, typically the default router for MN
• Care-of Address (COA)
– address of the current tunnel end-point for the MN (at FA or MN)
– actual location of the MN from an IP point of view
Tunneling
An encapsulating IP packet including a path and an original IP packet
IP-in-IP encapsulation
IP-in-IP encapsulation
• IP-in-IP-encapsulation (mandatory in RFC 2003)
– tunnel between HA and COA
Care-of address COA
IP address of HA
TTL
IP identification
IP-in-IP IP checksum
flags fragment offset
lengthTOSver. IHL
IP address of MN
IP address of CN
TTL
IP identification
lay. 4 prot. IP checksum
flags fragment offset
lengthTOSver. IHL
TCP/UDP/ ... payload
3
Mobile IP and IPv6
Mobile IP was developed for IPv4, but IPv6 simplifies the protocols
Security is integrated and not an add-on, authentication of registration is included
COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address
auto configuration
No need for a separate FA, all routers perform router advertisement which can be used instead of the
special agent advertisement;
Addresses are always co-located
MN can signal a sender directly the COA, sending via HA not needed in this case (automatic
path optimization)
soft“hand-over, i.e. without packet loss, between two subnets is supported
MN sends the new COA to its old router
the old router encapsulates all incoming packets for the MN and forwards them to the new COA
Authentication is always granted
DHCP: Dynamic Host Configuration Protocol
Main idea: E.g WPI has pool of IP addresses it can “lease” to hosts for
short term use, claim back when done
Application
simplification of installation and maintenance of networked computers
Supplies systems with all necessary information, such as IP address, DNS server address, domain name,
subnet mask, default router etc.
enables automatic integration of systems into an Intranet or the Internet,
can be used to acquire a COA for Mobile IP
Client/Server-Model
the client sends via a MAC broadcast a request to the DHCP serve r (might be via a DHCP relay) client
relay server client
Dynamic Host Configuration Protocol (DHCP) is a network protocol for automatically assigning TCP/IP
information to client machines. Each DHCP client connects to the centrally-located DHCP server which
returns that client's network configuration, including the IP address, gateway, and DNS servers
DHCP is useful for automatic configuration of client network interfaces. When configuring the client
system, the administrator can choose DHCP and instead of entering an IP address, netmask, gateway, or
DNS servers. The client retrieves this information from the DHCP server. DHCP is also useful if an
administrator wants to change the IP addresses of a large number of systems. Instead of reconfiguring all
the systems, he can just edit one DHCP configuration file on the server for the new set of IP addresses. If
the DNS servers for an organization changes, the changes are made on the DHCP server, not on the DHCP
clients. Once the network is restarted on the clients (or the clients are rebooted), the changes take effect.
Furthermore, if a laptop or any type of mobile computer is configured for DHCP, it can be moved from
office to office without being reconfigured as long as each office has a DHCP server that allows it to
connect to the network.
4
Configuration File
The first step in configuring a DHCP server is to create the configuration file that stores the network
information for the clients. Global options can be declared for all clients, while other options can be
declared for individual client systems.
The configuration file can contain extra tabs or blank lines for easier formatting. Keywords are case-
insensitive and lines beginning with a hash mark (#) are considered comments.
Two DNS update schemes are currently implemented — the ad-hoc DNS update mode and the interim
DHCP-DNS interaction draft update mode. If and when these two are accepted as part of the Internet
Engineering Task Force (IETF) standards process, there will be a third mode — the standard DNS update
method. The DHCP server must be configured to use one of the two current schemes. Version 3.0b2pl11
and previous versions used the ad-hoc mode; however, it has been deprecated.
There are two types of statements in the configuration file:
Parameters — State how to perform a task, whether to perform a task, or what network
configuration options to send to the client.
Declarations — Describe the topology of the network, describe the clients, provide addresses for
the clients, or apply a group of parameters to a group of declarations.
Some parameters must start with the option keyword and are referred to as options. Options configure
DHCP options; whereas, parameters configure values that are not optional or control how the DHCP
server behaves.
In Example the routers, subnet-mask, domain-name, domain-name-servers, and time-offset options are used
for any host statements declared below it.
Additionally, a subnet can be declared, a subnet declaration must be included for every subnet in the
network. If it is not, the DHCP server fails to start.
In this example, there are global options for every DHCP client in the subnet and a range declared.
Clients are assigned an IP address within the range.
subnet 192.168.1.0 netmask 255.255.255.0 {
option routers 192.168.1.254;
option subnet-mask 255.255.255.0;
option domain-name "example.com";
option domain-name-servers 192.168.1.1;
option time-offset -18000; # Eastern Standard Time
range 192.168.1.10 192.168.1.100;
}
5
ROUTING
Motivation for Mobile IP
Routing
based on IP destination address, network prefix (e.g. 129.13.42)
determines physical subnet
change of physical subnet implies change of IP address to have a topological correct address
(standard IP) or needs special entries in the routing tables
Specific routes to end-systems?
change of all routing table entries to forward packets to the right destination
does not scale with the number of mobile hosts and frequent changes in the location, security
problems
Changing the IP-address?
adjust the host IP address depending on the current location
almost impossible to find a mobile system, DNS updates take to long time
Requirements to Mobile IP
Transparency
mobile end-systems keep their IP address
continuation of communication after interruption of link possible
point of connection to the fixed network can be changed
Compatibility
support of the same layer 2 protocols as IP
no changes to current end-systems and routers required
mobile end-systems can communicate with fixed systems
Security
authentication of all registration messages
Efficiency and scalability
only little additional messages to the mobile system required (connection typically via a low andwidth
radio link)
world-wide support of a large number of mobile systems in the whole
Internet
6
IPv6 availability
• Generally available with (new) versions of most operating systems.
• BSD, Linux 2.2 Solaris 8
• An option with Windows 2000/NT
• Most routers can support IPV6
• Supported in J2SDK/JRE 1.4
IPv6 Design Issues
• Overcome IPv4 scaling problem
• Lack of address space.
• Flexible transition mechanism.
• New routing capabilities.
• Quality of service.
• Security.
• Ability to add features in the future.
Mobile ad hoc networks
Standard Mobile IP needs an infrastructure
Home Agent/Foreign Agent in the fixed network DNS, routing etc. are not designed for mobility
Sometimes there is no infrastructure!
remote areas, ad-hoc meetings, disaster areas Cost can also be an argument against an infrastructure! no default router available every node should be able to forward
Traditional routing algorithms
Traditional algorithms are pro-active – i.e. operate independent of user-message demands. Suitable for
wired networks.
Distance Vector periodic exchange of messages with all physical neighbors that contain information about who
can be reached at what distance
selection of the shortest path if several paths available Link State
periodic notification of all routers about the current state of all physical links
routers get a complete picture of the network Example
ARPA packet radio network (1973), DV-Routing, up to 138 nodes every 7.5s exchange of routing tables including link quality updating of tables also by reception of packets routing problems solved with limited flooding
7
Problems of traditional routing algorithms
Dynamics of the topology
Frequent changes of connections, connection quality, participants Limited performance of mobile systems
periodic updates of routing tables need energy without contributing to the transmission of user data;
sleep modes difficult to realize
Limited bandwidth of the system is reduced even more due to the exchange of routing information
Links can be asymmetric, i.e., they can have a direction dependent transmission quality
Uncontrolled redundancy in links
Interference – ‘unplanned links’ (advantage?) DSDV (Destination Sequenced Distance Vector)
Early work
on demand version: AODV (Ad-hoc On-demand Distance Vector
Expansion of distance vector routing (but still pro-active) Sequence numbers for all routing updates
assures in-order execution of all updates avoids loops and inconsistencies
Decrease of update frequency (‘damping’)
store time between first and best announcement of a path inhibit update if it seems to be unstable (based on the stored time values)
Dynamic source routing Split routing into discovering a path and maintaining a path Discovering a path
Only if a path for sending packets to a certain destination is needed and no path is currently available (reactive algorithm) Maintaining a path
Only while the path is in use: make sure that it can be used continuously Path discovery
Broadcast a packet (Route Request) with destination address and unique ID
if a station receives a broadcast packet
if the station is the receiver (i.e., has the correct destination address) then return the packet to the sender
8
a ID) then Discard the packet
otherwise, append own address and broadcast packet
sender receives packet with the current path (address list) Maintaining paths
After sending a packet wait for a layer 2 acknowledgement (if applicable) listen into the medium to detect if other stations forward the packet (if possible) request an explicit acknowledgement
if a station encounters problems it can inform the sender of a packet or look-up a new path locally
ALTERNATIVE METRICS.
Mobile IP with reverse tunneling
Router accepts often only “topological correct“addresses (firewall!)
a packet from the MN encapsulated by the FA is now topological correct
furthermore multicast and TTL problems solved (TTL in the home network correct, but MN is to
far away from the receiver)
Reverse tunneling does not solve
problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms
(tunnel hijacking)
optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender
(double triangular routing)
The standard is backwards compatible
the extensions can be implemented easily and cooperate with current implementations without
these extensions
Agent Advertisements can carry requests for reverse tunneling
World Wide Web and mobility
Protocol (HTTP, Hypertext Transfer Protocol) and language
(HTML, Hypertext Markup Language) of the Web have not been designed for mobile applications and
mobile devices, thus creating many problems!
Typical transfer sizes
HTTP request: 100-350 byte
responses avg. <10 kbyte, header 160 byte, GIF 4.1kByte, JPEG
12.8 kbyte, HTML 5.6 kbyte
but also many large files that cannot be ignored
The Web is no file system
Web pages are not simple files to download
static and dynamic content, interaction with servers via forms, content transformation, push
technologies etc.
many hyperlinks, automatic loading and reloading, redirecting
a single click might have big consequences
UNIT 4 - NETWORK LAYER
1) What is generic routing encapsulation?
Generic routing encapsulation (GRE) is an encapsulation scheme which supports other network
protocols in addition to IP. It allows the encapsulation of packets of one protocol suite into the
payload portion of a packet of another protocol suite.
2) Define COA.
The COA (care of address) defines the current location of the MN from an IP point of view. All
IP packets sent to the MN are delivered to the COA, not directly to the IP address of the MN.
Packet delivery toward the MN is done using the tunnel.
3) What is meant by Transparency?
Mobility should remain invisible for many higher layer Protocols and applications. The only
affects of mobility should be a higher delay and lower bandwidth which are natural in the case of
mobile networks.
4) What is Generic Routing encapsulation?
Generic Routing encapsulation (GRE) allows the encapsulation of packets of one protocol suite
into the payload portion of a packet of another protocol suit.
5) What is Binding Request?
Any node that wants to know the current location of an MN can send a binding request to the
HA. The HA can check if the MN has allowed dissemination of its current location.
6) What are the possibilities for the location of care-of-address (COA)?
The two possibilities for the location of care-of-address are:
i. Foreign agent COA
ii.Co-related COA
7) What are the requirements for the development of mobile IP standard?
The requirements are:
a.Compatibility
b.Transparency
c.Scalability and efficiency
d.Security
8) What is Dynamic source Routing?
Dynamic Source Routing eliminates all periodic routing updates. If a node needs to discover a
route, it broadcast a route request with a unique identifier and the destination address as
parameters. Any node that receivers a route request gives a list of addresses representing a
possible path on its way toward the destination.
9) Why is need of routing?
Routing is to find the path between source and destination and to forward the packets
appropriately.
10) Define Mobile node:
Mobile node:
A mobile node is an end-system or router that can change its point of attachment to the Internet
using mobile IP. The MN keeps its IP address and can continuously with any other system in the
Internet as long as link layer connectivity is given.
11) What is Encapsulation and Decapsulation?
Encapsulation is the mechanism of taking a packet consisting of packet header and data and
putting it into the data part of a new packet. The reverse operation, taking a packet out of the data
part of another packet, is called decapsulation.
12) Define Dynamic source routing.
In an adhoc networks where nodes exchanges packets from time to time. Dynamic Source
routing divides the task of routing into two separate problems:
i) Routing Recovery: A node only tries to discover a route to destination if it has to send
something to this destination and there is currently no known route
ii) Route Maintenance: If a node is continuously sending packets via route, it has to make sure
that the route is held urgent. As soon as a node detects problem with the current route it has to
find an alternative node.
13) Define Compatibility.
support of the same layer 2 protocols as IP
no changes to current end-systems and routers required
mobile end-systems can communicate with fixed systems
14) What is Home Agent (HA)?
Home Agent (HA)
system in the home network of the MN, typically a router
registers the location of the MN, tunnels IP datagrams to the COA
15) Define Foreign Agent (FA).
system in the current foreign network of the MN, typically a router
forwards the tunneled datagrams to the MN, typically also the default router for the MN
16) Define Agent Advertisement.
HA and FA periodically send advertisement messages into their physical subnets
MN listens to these messages and detects, if it is in the home or a foreign network
MN reads a COA from the FA advertisement messages
17) Define Registration.
MN signals COA to the HA via the FA, HA acknowledges via FA to MN
these actions have to be secured by authentication
18) Define Key distribution
Home agent distributes session keys
foreign agent has a security association with the home agent
mobile host registers a new binding at the home agent
home agent answers with a new session key for foreign agent and mobile node
19) Applications of Dynamic Host Configuration Protocol.
simplification of installation and maintenance of networked computers
supplies systems with all necessary information, such as IP address, DNS server address,
domain name, subnet mask, default router etc.
enables automatic integration of systems into an Intranet or the Internet, can be used to
acquire a COA for Mobile IP
20) Define DSDV (Destination Sequenced Distance Vector).
Expansion of distance vector routing
Sequence numbers for all routing updates
assures in-order execution of all updates
avoids loops and inconsistencies
21) List the examples for interference based routing.
Least Interference Routing (LIR)
calculate the cost of a path based on the number of stations that can receive a transmission
Max-Min Residual Capacity Routing (MMRCR)
calculate the cost of a path based on a probability function of successful transmissions and
interference
Least Resistance Routing (LRR)
calculate the cost of a path based on interference, jamming and other transmissions
LIR is very simple to implement
UNIT4 NETWORK LAYER
Part B
1. Explain mobile IP in detail.
Goals, assumptions and requirements – Entities and terminology – IP packet delivery – Agent
discovery – Agent advertisement, Agent solicitation –Registration – Tunneling and
encapsulation- IP-in-IP encapsulation, minimal encapsulation, generic routing encapsulation –
optimizations – Reverse tunneling – IPv6.
2. Give a detailed account of mobile ad-hoc networks.
Instant infrastructure, Disaster relief Remote areas Effectiveness – Routing – Asymmetric links,
redundant links, interference, dynamic topology – Destination sequence distance vector –
sequence numbers, damping - Dynamic source routing – route discovery, route maintenance -
Alternative metrics – least interference routing.
3. Explain about DHCP: Dynamic Host Configuration Protocol.
Application
Client/Server-Model
DHCP - protocol mechanisms
DHCP characteristics
4. Discuss about Adhoc-networks.
Standard Mobile IP needs an infrastructure
Routing
Routing examples for an ad-hoc network
5. Explain about Traditional routing algorithms in detail.
Distance Vector- Link State
6. Explain about DSDV (Destination Sequenced Distance Vector) in detail.
Expansion of distance vector routing
Sequence numbers for all routing updates
Decrease of update frequency
7 .State Dynamic source routing in detail.
Discover a path
Maintaining a path Optimizations
8. Discuss about inference routing in detail.
Least Interference Routing (LIR)
Max-Min Residual Capacity Routing (MMRCR)
Least Resistance Routing (LRR)
1
UNIT V
TRANSPORT AND APPLICATION LAYERS
Traditional TCP – Classical TCP improvements – WAP, WAP 2.0.
TRADITIONAL TCP
TCP is an alternative transport layer protocol over IP.
• TCP provides:
• Connection-oriented
• Reliable
• Full-duplex
• Byte-Stream
Connection-Oriented
• Connection oriented means that a virtual connection is established before any user data is transferred.
• If the connection cannot be established - the user program is notified.
• If the connection is ever interrupted - the user program(s) is notified.
Reliable
• Reliable means that every transmission of data is acknowledged by the receiver.
• If the sender does not receive acknowledgement within a specified amount of time, the sender retransmits
the data
Byte Stream
• Stream means that the connection is treated as a stream of bytes.
• The user application does not need to package data in individual datagrams (as with UDP).
Buffering
• TCP is responsible for buffering data and determining when it is time to send a datagram.
• It is possible for an application to tell TCP to send the data it has buffered without waiting for a buffer to fill
up.
Full Duplex
• TCP provides transfer in both directions.
• To the application program these appear as 2 unrelated data streams, although TCP can piggyback control
and data communication by providing control information (such as an ACK) along with user data.
TCP Ports
• Interprocess communication via TCP is achieved with the use of ports (just like UDP).
• UDP ports have no relation to TCP ports (different name spaces).
TCP Segments
• The chunk of data that TCP asks IP to deliver is called a TCP segment.
• Each segment contains:
• data bytes from the byte stream
• control information that identifies the data bytes
2
TCP Lingo
• When a client requests a connection it sends a “SYN” segment (a special TCP segment) to the server port.
• SYN stands for synchronize. The SYN message includes the client’s ISN.
• ISN is Initial Sequence Number.
• Every TCP segment includes a Sequence Number that refers to the first byte of data included in the
segment.
• Every TCP segment includes an Acknowledgement Number that indicates the byte number of the next data
that is expected to be received.
• All bytes up through this number have already been received.
• There are a bunch of control flags:
• URG: urgent data included.
• ACK: this segment is (among other things) an acknowledgement.
• RST: error – connection must be reset.
• SYN: synchronize Sequence Numbers (setup)
• FIN: polite connection termination
• MSS: Maximum segment size (A TCP option)
• Window: Every ACK includes a Window field that tells the sender how many bytes it can send before the
receiver will have to toss it away (due to fixed buffer size).
CLASSICAL TCP IMPROVEMENTS
TCP Connection Creation
• Programming details later - for now we are concerned with the actual communication.
• A server accepts a connection.
• Must be looking for new connections!
• A client requests a connection.
• Must know where the server is!
Client Starts
• A client starts by sending a SYN segment with the following information:
• Client’s ISN (generated pseudo-randomly)
• Maximum Receive Window for client.
• Optionally (but usually) MSS (largest datagram accepted).
• No payload! (Only TCP headers)
Server Response
• When a waiting server sees a new connection request, the server sends back a SYN segment with:
• Server’s ISN (generated pseudo-randomly)
• Request Number is Client ISN+1
• Maximum Receive Window for server.
• Optionally (but usually) MSS
• No payload! (Only TCP headers)
• When the Server’s SYN is received, the client sends back an ACK with:
• Acknowledgment Number is Server’s ISN+1
3
TCP 3-way handshake
Client: “I want to talk, and I’m starting with byte number X”.
Server: “OK, I’m here and I’ll talk. My first byte will be called number Y, and I know your first byte will be
number X+1”.
Client: “Got it - you start at byte number Y+1”.
Bill: “Monica, I’m afraid I’ll syn and byte your ack”
TCP Data and ACK
• Once the connection is established, data can be sent.
• Each data segment includes a sequence number identifying the first byte in the segment.
• Each segment (data or empty) includes a request number indicating what data has been received
Buffering
• Keep in mind that TCP is part of the Operating System. The O.S. takes care of all these details
asynchronously.
• The TCP layer doesn’t know when the application will ask for any received data.
• TCP buffers incoming data so it’s ready when we ask for it.
TCP Buffers
• Both the client and server allocate buffers to hold incoming and outgoing data
• The TCP layer does this.
• Both the client and server announce with every ACK how much buffer space remains (the Window field in
a TCP segment).
Send Buffers
• The application gives the TCP layer some data to send.
• The data is put in a send buffer, where it stays until the data is ACK’d.
• The TCP layer won’t accept data from the application unless (or until) there is buffer space.
ACKs
• A receiver doesn’t have to ACK every segment (it can ACK many segments with a single ACK segment).
• Each ACK can also contain outgoing data (piggybacking).
• If a sender doesn’t get an ACK after some time limit, it resends the data.
TCP Segment Order
• Most TCP implementations will accept out-of-order segments (if there is room in the buffer).
• Once the missing segments arrive, a single ACK can be sent for the whole thing.
• Remember: IP delivers TCP segments, and IP is not reliable - IP datagrams can be lost or arrive out of
order.
Termination
• The TCP layer can send a RST segment that terminates a connection if something is wrong.
• Usually the application tells TCP to terminate the connection politely with a FIN segment.
4
TCP Sockets Programming
• Creating a passive mode (server) socket.
• Establishing an application-level connection.
• Sending/receiving data.
• Terminating a connection.
Establishing a passive mode TCP socket
Passive mode:
• Address already determined.
• Tell the kernel to accept incoming connection requests directed at the socket address.
• 3-way handshake
• Tell the kernel to queue incoming connections for us.
Accepting an incoming connection
• Once we start listening on a socket, the O.S. will queue incoming connections
• Handles the 3-way handshake
• Queues up multiple connections.
• When our application is ready to handle a new connection, we need to ask the O.S. for the next connection.
Terminating a TCP connection
• Either end of the connection can call the close() system call.
• If the other end has closed the connection, and there is no buffered data, reading from a TCP socket returns
0 to indicate EOF
Client Code
• TCP clients can connect to a server, which:
• takes care of establishing an endpoint address for the client socket.
• don’t need to call bind first, the O.S. will take care of assigning the local endpoint address
(TCP port number, IP address).
• Attempts to establish a connection to the specified server.
• 3-way handshake
Reading from a TCP socket
• By default read() will block until data is available.
• Reading from a TCP socket may return less than max bytes (whatever is available).
• You must be prepared to read data 1 byte at a time!
WIRELESS APPLICATION PROTOCOL (WAP)
Empowers mobile users with wireless devices to easily access and interact with information and services.
A “standard” created by wireless and Internet companies to enable Internet access from a cellular phone
WAP: Main Features
Browser
– “Micro browser”, similar to existing web browsers
Markup language
– Similar to HTML, adapted to mobile devices
5
Script language
– Similar to Javascript, adapted to mobile devices
Gateway
– Transition from wireless to wired world
Server
– “Wap/Origin server”, similar to existing web servers
Protocol layers
– Transport layer, security layer, session layer etc.
Telephony application interface
– Access to telephony functions
Internet Model
WAP Architecture
HTML
HTTP
TLS/SSL
TCP/IP
6
WAP Application Server
WAP: Network Elements
WAP Specifies
Wireless Application Environment
– WML Microbrowser
– WMLScript Virtual Machine
– WMLScript Standard Library
– Wireless Telephony Application Interface (WTAI)
– WAP content types
Wireless Protocol Stack
– Wireless Session Protocol (WSP)
– Wireless Transport Layer Security (WTLS)
– Wireless Transaction Protocol (WTP)
– Wireless Datagram Protocol (WDP)
– Wireless network interface definitions
7
WAP Stack
WAE (Wireless Application Environment):
– Architecture: application model, browser, gateway, server
– WML: XML-Syntax, based on card stacks, variables, ...
– WTA: telephone services, such as call control, phone book etc.
WSP (Wireless Session Protocol):
– Provides HTTP 1.1 functionality
– Supports session management, security, etc.
WTP (Wireless Transaction Protocol):
– Provides reliable message transfer mechanisms
– Based on ideas from TCP/RPC
WTLS (Wireless Transport Layer Security):
– Provides data integrity, privacy, authentication functions
– Based on ideas from TLS/SSL
WDP (Wireless Datagram Protocol):
– Provides transport layer functions
– Based on ideas from UDP
WHY WAP?
Wireless networks and phones
– have specific needs and requirements
– not addressed by existing Internet technologies
WAP
– Enables any data transport
• TCP/IP, UDP/IP, GUTS (IS-135/6), SMS, or USSD.
– Optimizes the content and air-link protocols
– Utilizes plain Web HTTP 1.1 servers
• leverages existing development methodologies
8
• utilizes standard Internet markup language technology (XML)
• all WML content is accessed via HTTP 1.1 requests
– WML UI components map well onto existing mobile phone user interfaces
• no re-education of the end-users
• leveraging market penetration of mobile devices
– Several modular entities together form a fully compliant Internet entity
WAP: “Killer” Applications
Location-based services
– Real-time traffic reporting, Event/restaurant recommendation
Enterprise solutions
– Email access, Database access, “global” intranet access
– Information updates “pushed” to WAP devices
Financial services
– Banking, Bill-paying, Stock trading, Funds transfers
Travel services
– Schedules and rescheduling, Reservations
Gaming and Entertainment
– Online, real-time, multi-player games
– Downloadable horoscopes, cartoons, quotes, advice
M-Commerce
– Shopping on the go
– Instant comparison shopping
– Location-based special offers and sales
Wireless Application Environment (WAE)
Goals
– device and network independent application environment
– for low-bandwidth, wireless devices
– considerations of slow links, limited memory, low computing power, small display, simple user
interface (compared to desktops)
– integrated Internet/WWW programming model
– high interoperability
WAE Components
Architecture
– Application model, Microbrowser, Gateway, Server
User Agents
– WML/WTA/Others
– content formats: vCard, vCalendar, Wireless Bitmap, WML, ...
WML
– XML-Syntax, based on card stacks, variables, ...
WMLScript
– procedural, loops, conditions, ... (similar to JavaScript)
WTA
– telephone services, such as call control, text messages, phone book, ... (accessible from
WML/WMLScript)
Proxy (Method/Push)
9
WAE: Logical Model
WML: Wireless Markup Language
Tag-based browsing language:
– Screen management (text, images)
– Data input (text, selection lists, etc.)
– Hyperlinks & navigation support
Takes into account limited display, navigation capabilities of devices
XML-based language
– describes only intent of interaction in an abstract manner
– presentation depends upon device capabilities
Cards and Decks
– document consists of many cards
– User interactions are split into cards
– Explicit navigation between cards
– cards are grouped to decks
– deck is similar to HTML page, unit of content transmission
Events, variables and state mgmt
The basic unit is a card. Cards are grouped together into Decks Document ~ Deck (unit of transfer)
All decks must contain
– Document prologue
XML & document type declaration
– <WML> element
Must contain one or more cards
WML Example
WML>
<CARD>
<DO TYPE=“ACCEPT”>
<GO URL=“#eCard”/>
</DO
Welcome!
</CARD>
<CARD NAME=“eCard”>
<DO TYPE=“ACCEPT”>
<GO URL=“/submit?N=$(N)&S=$(S)”/>
</DO>
Enter name: <INPUT KEY=“N”/>
Choose speed:
10
<SELECT KEY=“S”>
<OPTION VALUE=“0”>Fast</OPTION>
<OPTION VALUE=“1”>Slow</OPTION>
<SELECT>
</CARD>
</WML>
WMLScript
Complement to WML
– Derived from JavaScript™
Provides general scripting capabilities
– Procedural logic, loops, conditionals, etc.
– Optimized for small-memory, small-cpu devices
Features
– local user interaction, validity check of user input
– access to device facilities (phone call, address book etc.)
– extensions to the device software
• configure device, download new functionality after deployment
Bytecode-based virtual machine
– Stack-oriented design, ROM-able
– Designed for simple, low-impact implementation
WMLScript compiler resides in the network
WMLScript Libraries
Lang - VM constants, general-purpose math functionality, etc.
String - string processing functions
URL - URL processing
Browser - WML browser interface
Dialog - simple user interface
Float - floating point functions
Wireless Telephony Application (WTA)
Collection of telephony specific extensions
– designed primarily for network operators
Example
– calling a number (WML)
wtai://wp/mc;07216086415
– calling a number (WMLScript)
WTAPublic.makeCall("07216086415");
Implementation
– Extension of basic WAE application model
– Extensions added to standard WML/WMLScript browser
– Exposes additional API (WTAI)
WTA Features
Extension of basic WAE application model
– network model for interaction
11
• client requests to server
• event signaling: server can push content to the client
– event handling
• table indicating how to react on certain events from the network
• client may now be able to handle unknown events
– telephony functions
• some application on the client may access telephony functions
WTAI includes:
– Call control
– Network text messaging
– Phone book interface
– Event processing
Security model: segregation
– Separate WTA browser
– Separate WTA port
WAP Push Services
Web push
– Scheduled pull by client (browser)
• example: Active Channels
– no real-time alerting/response
• example: stock quotes
Wireless push
– accomplished by using the network itself
• example: SMS
– limited to simple text, cannot be used as starting point for service
• example: if SMS contains news, user cannot request specific news item
WAP push
– Network supported push of WML content
• example: Alerts or service indications
– Pre-caching of data (channels/resources)
Push Access Protocol
Based on request/response model
Push initiator is the client
Push proxy is the server
Initiator uses HTTP POST to send push message to proxy
Initiator sends control information as an XML document, and content for mobile (as WML)
Proxy sends XML entity in response indicating submission status
Initiator can
– cancel previous push
– query status of push
– query status/capabilities of device
Push Proxy Gateway
WAP stack (communication with mobile device)
TCP/IP stack (communication with Internet push initiator)
Proxy layer does
– control information parsing
– content transformation
– session management
12
– client capabilities
– store and forward
– prioritization
– address resolution
– management function
WTP Services and Protocols
WTP (Transaction)
– provides reliable data transfer based on request/reply paradigm
• no explicit connection setup or tear down
• optimized setup (data carried in first packet of protocol exchange)
• seeks to reduce 3-way handshake on initial request
– supports
• header compression
• segmentation /re-assembly
• retransmission of lost packets
• selective-retransmission
• port number addressing (UDP ports numbers)
• flow control
– message oriented (not stream)
– supports an Abort function for outstanding requests
– supports concatenation of PDUs
– supports User acknowledgement or Stack acknowledgement option
• acks may be forced from the WTP user (upper layer)
• default is stack ack
WAP 2.0.
WSP - Wireless Session Protocol
Goals
– HTTP 1.1 functionality
• Request/reply, content type negotiation, ...
– support of client/server transactions, push technology
– key management, authentication, Internet security services
WSP Services
– provides shared state between client and server, optimizes content transfer
– session management (establish, release, suspend, resume)
– efficient capability negotiation
– content encoding
– push
WSP/B (Browsing)
– HTTP/1.1 functionality - but binary encoded
– exchange of session headers
– push and pull data transfer
– asynchronous requests
WSP Overview
Header Encoding
– compact binary encoding of headers, content type identifiers and other well-known textual or
structured values
– reduces the data actually sent over the network
Capabilities (are defined for):
13
– message size, client and server
– protocol options: Confirmed Push Facility, Push Facility, Session Suspend Facility,
Acknowledgement headers
– maximum outstanding requests
– extended methods
– header code pages
Suspend and Resume
– server knows when client can accept a push
– multi-bearer devices
– dynamic addressing
– allows the release of underlying bearer resources
Session Context and Push
– push can take advantage of session headers
– server knows when client can accept a push
Connection-mode
– long-lived communication, benefits of the session state, reliability
Connectionless-mode
– stateless applications, no session creation overhead, no reliability overhead
WAP: Ongoing Work
WDP
– Tunnel to support WAP where no (end-to-end) IP bearer available
WTLS
– support for end-to-end security (extending WTLS endpoint beyond WAP Gateway)
– interoperable between WAP and Internet (public key infrastructure)
– integrating Smart Cards for security functions
WTP
– efficient transport over wireless links (wireless TCP)
– bearer selection/switching
– quality of service definitions
WSP
– quality of service parameters
– multicast data, multimedia support
WAE
– User agent profiles: personalize for device characteristics, preferences etc
– Push architecture, asynchronous applications
– Billing
UNIT 5 - TRANSPORT AND APPLICATION LAYERS
Part A
1) What are the two functions of the transport layer in the internet?
The two functions of the transport layer in the internet are check summing over user data and
multiplexing/ demultiplexing of data from applications.
2) What is called the exponential growth of the congestion window?
The senders always calculate congestion window for a window start size of the congestion
window is one segment. Sender sends one packet and waits for acknowledgement. If
acknowledgement arises it raises the level of congestion window by one. If sender sends two
packets if acknowledgement arises it raises the level of congestion window by two. This scheme
raises the level of congestion window every time the acknowledges come back, which takes
round trip time (RTT).This is called the exponential growth of the congestion window
3) Advantages of I-TCP:
•I-TCP does not require any changes in the TCP protocol as used by the hosts in the fixed
network or other hosts in a wireless network that do not use this optimization.
•Without partitioning retransmission of lost packets would take place between mobile host and
correspondent host across the whole network.
•Optimization of new mechanisms is quite simple to be done in I-TCP as they only cover a single
hop.
•The short delay between the mobile host and foreign agent can be determined and is
independent of other traffic streams. Therefore an optimized TCP can use precise time-outs to
guarantee retransmission as fast as possible.
•Partitioning into two connections also allows the use of a different transport layer protocol
between the foreign agent and the mobile host or the use of compressed headers etc. The foreign
agent can act as a gateway to translate between different protocols.
4) Disadvantages of I-TCP:
• The loss of the end to end semantics of TCP cause problems if the foreign agent portioning the
TCP connection crashes.
• An increased handover latency is more problematic in practical use
• The foreign agent must be a trusted entity because the TCP connections end at this point.
5) Define Slow Start?
TCP’s reaction to a missing acknowledgement is quite drastic, but necessary to get rid of
congestion. The behaviour TCP shows after the detection of congestion is called Slow start.
6) How does data transmission takes place?
Data transmission takes place using network adapters, fibre optics, copper wires, special
hardware for routers etc.
7) What is mean by SCPS-TP?
The set of protocols developed for space communication is known as space communications
protocol standards (SCPS), the extended TCP is called SCPS-transport protocols.(SCPS-TP).
8) What are Advantage and Disadvantage of MobileTCP?
Advantage:
i. M-TCP maintains the TCP end-to-end semantice. The SH does not send any ACK itself but
forwards the ACKs from the MH.
ii.If the MH is disconnected, M_TCP avoids useless retransmissions, slow starts or breaking
connections by simply shrinking the sender’s window to 0;
iii. Since M-TCP does not buffer data in the SH as I-TCP does, it is not necessary to forward
buffers to a new SH. Lost packets will be automatically retransmitted to the new SH.
Disadvantage:
i. As the SH does not act as proxy as in I-TCP, packet loss on the wireless link due to bit errors is
propagated to the sender. M-TCP assumes low bit error rates, which is not always a valid
assumption.
ii. A modified TCP on the wireless link not only requires modification to the MH protocol
software but also new network elements like the bandwidth manager.
9) What is fast retransmit?
In TCP, a receiver sends acknowledgements only if it receive any packets from the sender. Thus
receiving acknowledgements from a receiver shows additionally that the receiver continuously
receives something from the sender. Therefore, the gap in the packet stream is not due to severe
congestion, but a simple packet loss due to a transmission error. The sender can now retransmit
the missing packets before the timer expires. This behaviour is called fast retransmit.
10) What is fast recovery?
The receipt of acknowledgement shows that there is no congestion justifying a slow start. The
sender can continue with the current congestion window. The sender performs a fast recovery
from the packet loss. This mechanism can improve the efficiency of TCP dramatically.
11) What is HTTP?
The Hypertext transfer protocol is a stateless, lightweight, application level protocol for data
transfer between servers and clients. An HTTP transaction consists of an HTTP request issued by
a client and an HTTP response from the server. Stateless means that all HTTP transactions
independent of each other.
12) What is image scaling?
If a page contains a true color, high-resolution picture, this picture can be scaled down to fewer
colors, lower resolution, or finally to only the title of the picture. The user can decide to
download the picture separately. Further one can offer clipping, zooming, or detail studies to
users if they are interested in a part of the picture.
13) What is WAP?
Wireless application protocol (WAP) is a common effort of many companies and organizations
to set up a framework for wireless and mobile web access using many different transport
systems. Eg. GSM, GPRS, UMTS.
14) What is WMLBrowser?
WMLBrowser is a library that provides several functions typical for a browser, such as prev to
go back one card or refresh to update the context of the user interface.
15) Define Damping
Transient changes in topology that are short duration should not destabilize the routing
mechanism. Advertisements containing changes in topology currently stored are therefore not
disseminated further. A node waits with dissemination if these changes are most likely not yet
stable.Waitingg time depends on the time between the first and the best announcement.
1
UNIT5 TRANSPORT AND APPLICATION LAYERS
Part B
1. Write notes on traditional TCP.
Congestion controls, slow start, fast retransmit/ fast recovery, implications on mobility.
2. Write notes on wireless TCP.
Indirect TCP, snooping TCP, Mobile TCP, Fast retransmit/fast recovery,
transmission/time-out freezing, selective retransmission, transaction oriented TCP.
3. Write notes on WDP and WTLS.
Figure and explanation about WDP and WTLS.
4. Write notes on wireless transaction protocol.
Figure and explanation about WTP class 0, class 1 and class 2.
5. Write notes on wireless sessions protocol.
WSP/B over WTP and WSP/ B as connectionless session service
6. Explain Traditional TCP
Architecture-Types- Frame formats-Explanation
7. Explain in detail about WAP.
Architecture-Types-Forum-Advantages-Disadvantages
8. Discuss about WMLBrowser.
Browser library-functions-Security.
MOBILE COMPUTING
UNIT 1 WIRELESS COMMUNICATION FUNDAMENTALS
TWO MARK QUESTIONS IN UNIT-1
1. Define CDMA.
2. Define Signal.
3. What is digital modulation?
4. Define code division multiplexing.
5. List out the advantages of frequency division multiplexing.
6. What are the several versions in CSMA?
7. What is Quadrature Amplitude Modulation?
8. What are the 2 sub layers in DLC?
9. Define time division multiplexing.
10. List out the different types of frequencies used for data transmission.
11. Define Antenna.
12. List out the different types of antennas.
13. Define Modulation.
14. What is hidden and exposed terminal problem?
15. Define polling.
16. What is spread spectrum?
17. List out the different types of spread spectrum techniques.
18. Distinguish between ALOHA and slotted ALOHA.
19. Define fading.
20. Distinguish between DSSS and FHSS.
21. What are the 3 fundamental propagation behaviors depending on their frequency?
22. What is multipath propagation?
23. What is guard space?
24. What are the 3 different basic schemes analog modulations?
25. What is the use of Phase Lock Loop (PLL)?
26. What is hopping sequence?
27. What is dwell time?
28. What are the advantages of cellular systems?
29. What is browsing channel allocation and fixed channel allocation?
30. What are the disadvantages of cellular systems?
31. What is digital sense multiple access?
32. What is Network and Switching subsystem?
33. What is authentication centre?
34. What is called burst and normal burst?
35. What are the basic groups of logical channels?
36. Define traffic multiframe and control multiframe?
BIG QUESTIONS IN UNIT-1
1. Explain different TDMA schemes in detail.
2. Explain multiplexing in detail.
3. Discuss Modulation techniques in detail.
4. Account on CDMA Scheme.
5. Explain FDMA in detail.
6. Discuss SDMA in detail.
7. Explain major types of networks.
8. Explain types of Antennas in detail.
9. Explain the various applications of mobile computing.
10. Explain about the signal propagation.
11. Discuss about the cellular system.
12. List the difference between S/T/F/CDMA.
13. What is spread spectrum with its types.
14. Why do MAC scheme in wired network fail in wireless networks and how dose the
multiple access with collision avoidance (MACA) scheme work.
15. Define modulation and explain the method for analog modulation techniques in
details.
16. Discuss briefly the advanced phase shift keying.
UNIT II TELECOMMUNICATION SYSTEMS
TWO MARK QUESTIONS IN UNIT-II
1. What is Handover?
2. What are the categories of Mobile services?
3. What is TETRA?
4. What is meant by GPRS?
5. What are subsystems in GSM system?
6. What is meant by GEO?
7. Define the inclination angle and perigee.
8. Define the elevation angle and footprint.
9. What is MSC?
10. What are the different types of disk?
11. What are the goals of DVB?
12. Name some of the formats supported by MOT?
13. What are the advantages of DAB?
14. What is object repetition?
15. What is EIT?
16. What are the service information sent by DVB?
17. What is Active scanning?
18. What is Passive Scanning?
19. What is FIC?
20. What are the registers maintained by the gateway of satellite?
21. Specify the security services offered by GSM.
22. What is the frequency range of uplink and downlink in GSM network?
23. What are the two basic groups of logical channels in GSM?
24. What are the control channel groups in GSM?
25. List out the numbers needed to locate an MS and to address the MS.
26. What are the four possible handover scenarios in GSM?
27. What are the security services offered by GSM?
28. What is meant by GGSN?
29. What is meant by SGSN?
30. What is meant by BSSGP?
31. Define the protocol architecture of DECT.
32. Specify the standards offered by TETRA.
33. How many ITU standardized groups of 3G radio access technologies are there in
IMT-2000?
34. What are the steps perform during the search for a cell after power on?
35. What are the two basic classes of handover?
36. What are the two basic transport mechanisms used by DAB?
37. What are the two transport modes defined for MSC?
38. Define the terms: i. Earth Station. ii. Uplink.
39. Define Elevation Angle.
40. What are the factors limited the number of sub channels provided within the
satellite channel?
BIG QUESTIONS IN UNIT-II
1. Write notes on DECT and TETRA.
2. Write notes on UMTS and IMT – 2000.
3. Explain broadcast systems in detail.
4. Explain satellite systems in detail.
5. Explain GSM systems in detail.
6. Explain GPRS systems in detail.
7. Explain DAB in detail.
8. Explain DVB in detail.
9. Explain the following a) Routing b) Hand over c) Localization.
10. Explain the various satellite orbit and the parameters associated.
11. Compare GEO, MEO and LEO
UNIT III WIRELESS NETWORKS
TWO MARK QUESTIONS IN UNIT-3
1. What is the primary goal of IEE 802.11?
2. What is meant by SIFS?
3. What are Advantages of wireless LAN?
4. What are Design Goals of Wireless LAN?
5. What are the three Low Power States provided by Bluetooth?
6. What is SCO?
7. What are Advantages and Disadvantages of Infrared?
8. What are the system integration functions of MAC management?
9. What do you meant by roaming?.
10. What is mobile routing?
11. What are the functions which support service and connection control?
12. What are the examples for service scenarios identified in WATM ?
13. What is BRAN?
14. What are the different network types of BRAN?
15. What is the main problem for WATM during handover?
16. What are the different segments in ATM end-to-end connection?
17. What is anchor point? .
18. What are different types of handover?
19. What is mobile terminal and wireless terminal?.
20. Mention some of the disadvantages of WLANS?
21. Mention the design goals of WLANS?
22. What is the difference between infrastructure and ad-hoc networks?
23. Mention the features of infrared transmission?
24. What are the disadvantages of infrared transmission?
25. Mention the features of radio transmission?
26. What are the disadvantages of radio transmission?
27. Define frequency hopping spread spectrum?
28. Define random back off time?
29. What is Traffic Indication Map?
30. What is Delivery Traffic Indication Map?
31. What is Ad-hoc TIM?
32. Mention the features of HIPERLAN1?
33. What are the three phases of medium access in EY-NPMA?
34. Mention the elements of Bluetooth core protocols?
35. What is the purpose of sniff state?
36. What is the use of hold state?
37. What is the purpose of park state?
BIG QUESTIONS IN UNIT-3
1. Explain the architecture and features of IEEE 802.11 in details
2. Write notes on WATM services and Functions.
3. Write notes on WATM handover.
4. Write notes on location management, addressing and access point control
protocol.
5. Give a detail note on HYPERLAN
6. Account on BLUETOOTH in detail.
7. Discuss in detail about the different services of IEEE802.11.
8. Explain in detail about Adhoc networks.
9. List out the Advantages and Disadvantages of Infrastructure network and adhoc
network.
10. Explain the MAC layer in IEEE802.11
11. Explain how power management is done in IEEE 802.11 infrastructure based and
ad hoc networks.
12. Discuss how to increase the quality of service in an ad hoc network.
UNIT IV NETWORK LAYER
TWO MARK QUESTIONS IN UNIT-IV
1. What is generic routing encapsulation?
2. Define COA.
3. What is meant by Transparency?
4. What is Binding Request?
5. What are the possibilities for the location of care-of-address (COA)?
6. What are the requirements for the development of mobile IP standard?
7. Why is need of routing?
8. What is Dynamic source Routing?
9. Define Mobile node.
10. What is Encapsulation and Decapsulation?
11. Define Compatibility.
12. What is Home Agent (HA)?
13. Define Foreign Agent (FA).
14. Define Agent Advertisement.
15. Define Registration.
16. Define Key distribution.
17. Applications of Dynamic Host Configuration Protocol.
18. Define DSDV (Destination Sequenced Distance Vector).
19. List the examples for interference based routing.
20. Define tunneling.
21. What are the requirements of mobile IP?
22. Mention the different entities in a mobile IP.
23. What do you mean by mobility binding?
24. Define a tunnel.
25. Define an outer header
26. Define an inner header.
27. What is the use of network address translation?
28. Define triangular routing.
29. What is meant by a binding cache?
30. Define binding request.
31. What is known as Binding update?
32. Explain binding acknowledgement.
33. Define binding warning.
34. Explain cellular IP.
35. What are the advantages of cellular IP?
36. What is known as mobility anchor point?
37. Explain destination sequence distance vector routing.
38. What are the two things added to the distance vector algorithm?
39. How the dynamic source routing does divide the task of routing into two separate
problems?
BIG QUESTIONS IN UNIT-IV
1. Explain mobile IP in detail.
2. Give a detailed account of mobile ad-hoc networks.
3. Explain about DHCP: Dynamic Host Configuration Protocol.
4. Discuss about Adhoc-networks.
5. Explain about Traditional routing algorithms in detail.
6. Explain about DSDV (Destination Sequenced Distance Vector) in detail.
7. State Dynamic source routing in detail.
8. Discuss about inference routing in detail.
9. Explain the following :a)Agent Advertisement b)Encapsulation
10. Explain the following:a)Registration b)Tunneling.
11. a. What are the requirements of a mobile IP? (8) b. Describe Dynamic host
configuration protocol. (8)
12. a. Discuss the routing algorithm in ad-hoc network (8) b. What are the entities in
mobile IP? (8)
13. a. Discuss how optimization in achieved in mobile IP (8).b. Explain tunneling and
encapsulation in mobile IP. (8)
14. Explain how dynamic source routing protocols handles routing with an example
UNIT V TRANSPORT AND APPLICATION LAYERS
TWO MARK QUESTIONS IN UNIT-V
1. What are the two functions of the transport layer in the internet?
2. What is called the exponential growth of the congestion window?
3. List out the advantages of I-TCP.
4. List out disadvantages of I-TCP.
5. Define Slow Start.
6. How does data transmission takes place?
7. What is mean by Slow Start?
8. What is mean by SCPS-TP?
9. What are Advantages and Disadvantages of MobileTCP?
10. What is Fast retransmit?
11. What is fast recovery?
12. What is HTTP?
13. What is WAP?
14. What is WML Browser?
15. List out advantages of Transmission Freezing.
16. Define WAE.
17. What is WML?
18. Write short notes on WAP forum.
19. Distinguish between Traditional TCP and wireless TCP?
20. What is WTP? What are its classes?
21. List out the network elements of WAP.
22. What is the purpose of congestion window in classical TCP?
23. What is slow start?
24. What is the use of congestion threshold?
25. What led to the development of Indirect TCP?
26. What is the goal of M-TCP?
27. What do you mean by persistent mode?
28. What are the characteristics of 2.5G/3.5G wireless networks?
29. What are the configuration parameters to adapt TCP to wireless environments?
30. State the requirements of WAP.
31. Name the layers of WAP.
32. Name some ICMP messages.
33. What is WTP? What are its classes?
34. What is WSP?
35. Name some features of WSP adapted to web browsing.
36. What is WML?
37. What are the features of WML?
38. What are the advantages of WML Script over WML?
39. Name the libraries specified by WML Script.
40. What are the classes of libraries?
41. Name the operations performed by PAP.
42. What are the components of WAP2.0?
BIG QUESTIONS IN UNIT-V
1. Explain in detail about traditional TCP.
2. Explain about Classical TCP improvement techniques in detail.
3. Write notes on WDP and WTLS.
4. Write notes on wireless sessions protocol
5. Explain in detail about WAP.
6. Discuss about WAE and WTP.
7. Explain the following: Snooping TCP and Indirect TCP.
8. Explain the following: Selective repeat and Fast retransmit and recovery.
9. Explain the following: Freezing and transaction oriented TCP.
10. Explain about WML and WML script with the help of an example.
11. Explain classical TCP improvements and snooping TCP.
12. Explain the concept of wireless markup language.
13. Explain wireless application protocols with the it’s version WAP 2.0in detail.
Describe the operation of the window flow control mechanism
UNIT-1 WIRELESS COMMUNICATION FUNDAMENTALS
Part-1 (2 Marks)
1. What are the 3 fundamental propagation behaviors depending on their frequency?
2. What is multipath propagation?
3. What is guard space?
4. What is the 3 different basic shemes analog modulation?
5. What is the use of Phase Lock Loop (PLL)?
6. What is hopping sequence?
7. What is dwell time?
8. What are the advantages of cellular systems?
9. What is browsing channel allocation and fixed channel allocation?
10. What are the disadvantages of cellular systems?
11. What is digital sense multiple access?
12. What is Network and Switching subsystem?
13. What is authentication centre?
14. What is called burst and normal burst?
15. What are the basic groups of logical channels?
16. Define traffic multi frame and control multi frame?
17. What is OVSF?
18. Specify the steps perform during the search for a cell after power on?
19. Explain about transparent mode?
20. What are the basic classes of handovers?
Part -B
1. Explain about Mobile services (16)
2. Explain System architecture (16)
3. Explain briefly about TETRA (16)
4. Write brief about UMTS and IMT-2000(16)
5. Explain about UTRAN (16)
UNIT-2- TELECOMMUNICATION NETWORKS
Part -1(2 Marks)
1. Specify the security services offered by GSM.
2. What is the frequency range of uplink and downlink in GSM network?
3. What are the two basic groups of logical channels in GSM?
4. What are the control channel groups in GSM?
5. List out the numbers needed to locate an MS and to address the MS.
6. What are the four possible handover scenarios in GSM?
7. What are the security services offered by GSM?
8. What is meant by GGSN?
9. What is meant by SGSN?
10. What is meant by BSSGP?
11. Define the protocol architecture of DECT.
12. Specify the standards offered by TETRA.
13. How many ITU standardized groups of 3G radio access technologies are there in IMT-2000?
14. What are the steps perform during the search for a cell after power on?
15. What are the two basic classes of handover?
16. What are the two basic transport mechanisms used by DAB?
17. What are the two transport modes defined for MSC?
18. Define Elevation Angle.
19. What are the factors limited the number of sub channels provided within the satellite channel?
Part-B
1. Explain GSM architecture (16)
2. Explain Satellite networks in detail (16)
3. Write short notes on DAB (16)
4. Write short notes on DVB (16)
5. Explain about DECT (16)
UNIT-III WIRLESS LAN IT 1402 – MOBILE COMPUTING
Part-A (2 marks)
1. What are the advantages of WLANS?
2. Mention some of the disadvantages of WLANS?
3. Mention the design goals of WLANS?
4. What is the difference between infrastructure and ad-hoc networks?
6. Mention the features of infrared transmission?
7. What are the disadvantages of infrared transmission?
8. Mention the features of radio transmission?
10. Define frequency hopping spread spectrum?
11. Define random back off time?
12. What is Traffic Indication Map?
13. What is Delivery Traffic Indication Map?
14. What is Ad-hoc TIM?
15. What is meant by roaming?
16. Mention the features of HIPERLAN1?
17. What are the three phases of medium access in EY-NPMA?
18. Mention the elements of Bluetooth core protocols?
19. What is the purpose of sniff state?
20. What is the use of hold state?
21. What is the purpose of park state?
Part-B
1. Explain the architecture of IEEE 802.11(16)
2. Explain the MAC layer in IEEE802.11 (16)
3. Explain HIPERLAN 1 in detail HIPERLAN 1(16)
4. Explain about WATM (16)
5. Writ e short notes on Bluetooth. (16)
UNIT: 4- MOBILE NETWORK LAYER
Part –A (2 marks)
1. What are the requirements of mobile IP?
2. Mention the different entities in a mobile IP.
3. What do you mean by mobility binding?
4. Define a tunnel.
5. What is encapsulation?
6. What is decapsulation?
7. Define an outer header.
8. Define an inner header.
9. What is meant by generic routing encapsulation?
10. What is the use of network address translation?
11. Define triangular routing.
12. What is meant by a binding cache?
13. Define binding request.
14. What is known as Binding update?
15. Explain binding acknowledgement.
16. Define binding warning.
17. Explain cellular IP.
18. What are the advantages of cellular IP?
19. What is known as mobility anchor point?
20. Explain destination sequence distance vector routing
21. What are the two things added to the distance vector algorithm?
22. How the dynamic source routing does divide the task of routing into two separate problems?
Part -B
1. What are the requirements of a mobile IP? (16)
2. What are the entities in mobile IP? (16)
3. Explain tunneling and encapsulation in mobile IP. (16)
4. Describe Dynamic host configuration protocol. (16)
5. Explain routing in IPv6. (16)
UNIT-V TRANSPORT AND APPLICATION LAYERS
Part-A (2 marks)
1. What is slow start?
2. What is the use of congestion threshold?
3. What led to the development of Indirect TCP?
4. What is the goal of M-TCP?
5. What do you mean by persistent mode?
6. What are the characteristics of 2.5G/3.5G wireless networks?
7. What are the configuration parameters to adapt TCP to wireless environments?
8. State the requirements of WAP.
9. Name the layers of WAP.
10. Name some ICMP messages.
11. What is WTP? What are its classes?
12. What is WSP?
13. Name some features of WSP adapted to web browsing.
14. What is WML?
15. What are the features of WML?
16. What are the advantages of WML Script over WML?
17. Name the libraries specified by WMLScript.
18. What are the classes of libraries?
19. Name the operations performed by PAP.
20. What are the components of WAP2.0?
Part-B
1. Explain traditional TCP. (16)
2. Explain classical TCP improvements (16)
3. Write short notes on WAP (16)
IT1402 Mobile Computing 1
UNIT-1
WIRELESS COMMUNICATION FUNDAMENTALS
PART – A (2MARKS) 1. What are the 3 fundamental propagation behaviors depending on their
frequency?
2. What is multipath propagation?
3. What is guard space?
4. What is the 3 different basic schemes analog modulation?
5. What is the use of Phase Lock Loop (PLL)?
6. What is hopping sequence?
7. What is dwell time?
8. What are the advantages of cellular systems?
9. What is browsing channel allocation and fixed channel allocation?
10. What are the disadvantages of cellular systems?
11. What is digital sense multiple access?
12. What is Network and Switching subsystem?
13. What is authentication centre?
14. What is called burst and normal burst?
15. What are the basic groups of logical channels?
16. Define traffic multi frame and control multi frame?
17. What is OVSF?
18. Specify the steps perform during the search for a cell after power on?
19. Explain about transparent mode?
20. What are the basic classes of handovers?
21. When are tuning frequency and frequency considered?
22. How can you utilize mobile antennas efficiently?
23. Compare various modulation techniques.
24. Define the relation between the data rate and bandwidth. What has harmonics to do with bandwidth?
PART – B
1. Discuss briefly the multiplexing techniques. (16)
2. Explain about the signal propagation. (16)
3. Discuss about the cellular system. (16)
4. List the difference between SDMA /TDMA /FDMA/CDMA. (16)
5. What is spread spectrum with its types. (16)
6. Explain about the TDMA. (16)
7. Why CDMA is needed and explain it with an example? (16)
8.
Why do MAC scheme in wired network fail in wireless networks and how does the multiple
access with collision avoidance (MACA) scheme work? (16)
9. Define modulation and explain the method for analog modulation techniques in details. (16)
10. Discuss briefly the code division multiplexing techniques. (16)
11. Discuss briefly the advanced phase shift keying. (16)
12.
a. Explain about cellular wireless network. (08)
b. Explain about wireless transmission. (08)
IT1402 Mobile Computing 2
13. Consider three users and Barker code of six bits each for the users transmitting the signals,
introduce noise and near / far problem while transmitting and reconstruct the data in the
receiving side providing the proper counter measures for the complications.
(16)
14. a.
Table the frequency bands used for wireless applications with their ranges, propagation
models and applications. (08)
b.
Represent diagrammatically the protocol machines for multiple access with collision
avoidance. (08)
UNIT- 2
TELECOMMUNICATION NETWORKS
PART – A (2 MARKS)
1. Specify the security services offered by GSM.
2. What is the frequency range of uplink and downlink in GSM network?
3. What are the two basic groups of logical channels in GSM? 4. What are the control channel groups in GSM?
5. List out the numbers needed to locate an MS and to address the MS.
6. What are the four possible handover scenarios in GSM?
7. What is meant by GGSN?
8. What is meant by SGSN?
9. What is meant by BSSGP?
10. Define the protocol architecture of DECT.
11. Specify the standards offered by TETRA.
12. How many ITU standardized groups of 3G radio access technologies are there in
IMT-2000?
13. What are the steps perform during the search for a cell after power on?
14. What are the two basic classes of handover?
15. What are the two basic transport mechanisms used by DAB?
16. What are the two transport modes defined for MSC?
17. Define the terms:
i. Earth Station.
ii. Uplink. 18. Define Elevation Angle.
19. What are the factors limited the number of sub channels provided within the
satellite channel?
20. Differentiate Broadcast from Multicast.
21. Detail the features of MSAT.
22. How can an efficient routing be made in satellite systems? 23. What do you understand by co channel interference and adjacent?
24. Describe the services provided by GSM network.
PART – B
1. Explain GSM architecture. (16)
2. Explain Satellite networks in detail. (16)
3. Write short notes on DAB. (16)
4. Write short notes on DVB. (16)
5. Explain DECT. (16)
6. Explain in details the functioning of GPRS. (16)
7. Compare GEO, MEO and LEO (16)
IT1402 Mobile Computing 3
8. Sketch the data network in your campus. How many hosts are there and how large is
the user population? What is the speed of the access link to the Internet? How so you
gain access to the Internet? How much does home access to the Internet costs?
(16)
9.
a.
Consider a mobile user who is migrating from a place to another place provide him a
seamless service by satellite system, also sketch the architecture. (08)
b. Discuss the importance of DECT Protocol Layers. (08)
UNIT-3
WIRELESS LAN
PART – A (2 MARKS)
1. What are the advantages of WLANS? 2. Mention some of the disadvantages of WLANS. 3. Mention the design goals of WLANS. 4. What is the difference between infrastructure and ad-hoc networks? 6. Mention the features of infrared transmission. 7. What are the disadvantages of infrared transmission? 8. Mention the features of radio transmission. 9. What are the disadvantages of radio transmission? 10. Define frequency hopping spread spectrum. 11. Define random back off time. 12. What is Traffic Indication Map? 13. What is Delivery Traffic Indication Map? 14. What is Ad-hoc TIM? 15. What is meant by roaming? 16. Mention the features of HIPERLAN1. 17. What are the three phases of medium access in EY-NPMA? 18. Mention the elements of Bluetooth core protocols. 19. What is the purpose of sniff state? 20. What is the use of hold state? 21. What is the purpose of park state? 22. In what functionality Switches differ from Routers. PART – B
1. Explain the architecture and features of IEEE 802.11 in details. (16)
2. Explain the MAC layer in IEEE802.11. (16)
IT1402 Mobile Computing 4
3. Explain HIPERLAN in detail. (16)
4. Write short notes on Bluetooth. (16)
5. Explain the service offered by IEEE802.11 standard. (16)
6. Explain how power management is done in IEEE 802.11 infrastructure
based and ad hoc networks. (16)
7. Discuss how to increase the quality of service in an ad hoc network. (16)
8. a. Detail the time- bounded service on top of the standard DCF
mechanism where ad hoc networks cannot use the function. (08)
b. Discuss the PHY frame format of an IEEE 802.11 using the spread
spectrum technique which separates by code. (08) 9. a. The channel access control sublayer of HIPERLAN offers a connectionless
data transfer service to the higher MAC layer. Justify
the above statement with related references. (08)
b.Discuss the functionalities and support provided by L2CAP. (08)
UNIT - 4
MOBILE NETWORK LAYER
PART – A (2 MARKS)
1. What are the requirements of mobile IP?
2. Mention the different entities in a mobile IP.
3. What do you mean by mobility binding?
4. Define a tunnel.
5. What is encapsulation?
6. What is decapsulation?
7. Define an outer header
8. Define an inner header.
9. What is meant by generic routing encapsulation?
10. What is the use of network address translation?
11. Define triangular routing.
12. What is meant by a binding cache?
13. Define binding request.
14. What is known as Binding update?
15. Explain binding acknowledgement.
16. Define binding warning.
17. Explain cellular IP.
IT1402 Mobile Computing 5
18. What are the advantages of cellular IP? 19. What is known as mobility anchor point? 20. Explain destination sequence distance vector routing. 21. What are the two things added to the distance vector algorithm? 22. How the dynamic source routing does divide the task of routing into two
separate problems?
PART – B
1. a. What are the requirements of a mobile IP? (08)
b. Describe Dynamic host configuration protocol. (08)
2. a. Discuss the routing algorithm in ad-hoc network. (08)
b. What are the entities in mobile IP? (08)
3. a. Discuss how optimization in achieved in mobile IP. (08)
b. Explain tunneling and encapsulation in mobile IP. (08)
4. Explain how dynamic source routing protocols handles routing with an
example. (16)
5. Discuss and detail the differences in topology reorganization in DSDV
and DSR routing protocols. (16)
6. a. What are the general problems of mobile IP regarding security and
support of quality of service? (08)
b. Name the inefficiencies of mobile IP regarding data forwarding from a
correspondent node to a mobile node. What are optimizations and what
additional problems do they cause? (08)
UNIT- 5
TRANSPORT AND APPLICATION LAYERS
PART – A (2 MARKS) 1. What is slow start? 2. What is the use of congestion threshold? 3. What led to the development of Indirect TCP? 4. What is the goal of M-TCP? 5. What do you mean by persistent mode? 6. What are the characteristics of 2.5G/3.5G wireless networks? 7. What are the configuration parameters to adapt TCP to wireless
environments? 8. State the requirements of WAP.
9. Name the layers of WAP. 10. Name some ICMP messages. 11. What is WTP? What are its classes?
IT1402 Mobile Computing 6 12. What is WSP? 13. Name some features of WSP adapted to web browsing. 14. What is WML? 15. What are the features of WML? 16. What are the advantages of WML Script over WML? 17. Name the libraries specified by WML Script. 18. What are the classes of libraries? 19. Name the operations performed by PAP. 20. What are the components of WAP2.0? 21. How and why does I-TCP isolate problems on the wireless link?
PART – B
1. Explain in detail about traditional TCP in details. (16)
2. Explain classical TCP improvements and snooping TCP. (16)
3. Explain the function of the components of the WAP architecture. (16)
4. Explain the concept of wireless markup language. (16)
5. Explain wireless application protocols with the it’s version WAP 2.0 in
detail. (16)
6. Describe the operation of the window flow control mechanism. (16)
7. What are the major difference between WAP 2.0 and WAP 1.x? What
influenced the WAP 2.0 development? (16)
Model Exam1
Subject Name : Mobile Computing Max. Marks: 100 Duration : 3 Hrs
Answer all the questions
PART –A (10 x 2 = 20 Marks)
1. Why electromagnetic waves with very low frequency not used for data transmission?
2. What are main benefits of spread spectrum system?
3. What are the reasons for delays in GSM for packet data traffic?
4. Differentiate hard and soft handoff.
5. Why is the physical layer in IEEE 802.11 subdivided?
6. What is HIPERLAN?
7. What are the differences between AODV and standard distance vector algorithm?
8. What advantages does the use of IPV6 offer for mobility?
9. How does I-TCP isolate problems on wireless link?
10. List out the advantages of WAP.
PART-B (5 x 16 = 80 Marks)
11. (a) Explain in detail about multiplexing. (16)
(OR)
(b) Sketch the block diagram of transmitter and receiver of DSSS & FHSS. (16)
12. (a) Explain the functional and protocol architecture of GSM. (16)
(OR)
(b) Discuss the functional and protocol architecture of GPRs. (16)
13. (a) (i) Explain IEEE 802.11 protocol architecture and bridging with
other networks. (10)
(ii) How do IEEE 802.11 solve hidden terminal problems? Explain
With necessary diagrams. (6)
(OR)
(b) Discuss in detail about Bluetooth. (16)
14. (a) Explain any one reactive routing protocol in ad-hoc networks with an (16)
example.
(OR)
(b) Discuss ZRP and ODMR in detail. (16)
(OR)
15. (a) Compare and contrast I-TCP, Snooping TCP and M-TCP. (16)
(OR)
(b) Discuss briefly about WAP architecture.
Model Exam2
Subject Name : Mobile Computing Max. Marks: 100 Duration : 3 Hrs
Answer all the questions
PART –A (10 x 2 = 20 Marks)
1. Differentiate analog modulation and digital modulation.
2. How are guard spaces realized between users in CDMA?
3. What are the reasons for delays in GSM for packet data traffic?
4. How security is implemented in GSM?
5. Why is the physical layer in IEEE 802.11 subdivided?
6. What is DCF?
7. What are the differences between AODV and standard distance vector algorithm?
8. What advantages does the use of IPV6 offer for mobility?
9. Define fast retransmit.
10. What are the classes in WTP?
PART-B (5 x 16 = 80 Marks)
11. (a) Compare and contrast S/T/F/CDMA in detail. (16)
(OR)
(b) Explain in detail about spread spectrum techniques. (16)
12. (a) Explain the functional and protocol architecture of GSM. (16)
(OR)
(b) Discuss channel allocation and call routing in detail. (16)
13. (a) (i) Explain IEEE 802.11 MAC functions in detail. (10)
(ii) How do IEEE 802.11 solve hidden terminal problems? Explain
With necessary diagrams. (6)
(OR)
(b) Discuss in detail about HIPERLAN. (16)
14. (a) Explain the following with respect to IP.
(i) Agent Advertisement.
(ii) Tunneling.
(iii) Encapsulation.
(OR)
(b) Discuss about DSDV and DSR. (16)
(OR)
15. (a) Explain the TCP improvement techniques in detail. (16)
(OR)
(b) Discuss briefly about WTLS, WSP and WAE in WAP. (16)
Model Exam3
Subject Name : Mobile Computing Max. Marks: 100 Duration : 3 Hrs
Answer all the questions
PART –A (10 x 2 = 20 Marks)
1. What are the several versions in CSMA?
2. What is FDD?
3. What are types of Handover?
4. What is meant by beacon?
5. What are the advantages and disadvantages of infrared?
6. .What is the differences between AODV and standard distance vector algorithm?
7. What advantages does the use of IPV6 offer for mobility?
8. What are the requirements for the development of mobile IP?
9. Define slow start.
10. Define wml.
PART-B (5 x 16 = 80 Marks)
11. (a) Discuss signal propagation techniques in detail. (16)
(OR)
(b) Explain in detail about spread spectrum techniques. (16)
12. (a) Explain channel allocation and call routing in GSM. (16)
(OR)
(b) Discuss functional and protocol architecture of GPRs. (16)
13. (a) Explain in detail about Bluetooth. (16)
. (OR)
(b) Discuss in detail about HIPERLAN. (16)
14. (a) Explain the following with respect to IP.
(i) Agent Registration.
(ii) IP optimization.
(iii) Tunneling.
(OR)
(b) Discuss about DHCP in detail. (16)
15. (a) Explain I-TCP,M-TCP,S-TCP and Freezing TCP in detail. (16)
(OR)
(b) Discuss briefly about WAP architecture. (16)
Question paper code: D2286
B.E/B.Tech Degree Examination APRIL /MAY 2010
Eighth Semester
Computer Science and Engineering
IT1402-MOBILE COMPUTING
(Regulation 2004)
Answer all questions
Part -A(10*2=20)Marks
1 What is spreading factor?
2.What is polling?
3.Distinguish between soft handover& hard Hand over.
4.Define foot print with respect to satellite systems.
5.State the 3 phases of the medium access of different competing nodes.
6.what are the power saving mechanisms in bluetooth?
7.What are the drawbacks of wired networks?
8.Define Dynamic Source Routing.
9.What is the difference between TCP & UDP.
10. Mention any 2 salient features of WAP.
Part-B (5*16=80)Marks
11 (a) i Discuss in detail about the types of antennas with their radiation patterns.(12)
ii Explain Diversity techniques.(4)
[or]
11 (b) Explain space Frequency,code & Time division Multiplexing in detail.(16)
12 (a) Describe Digital Audio Broadcasting.(16)
[or]
(b) Explain routing ,localization and handover in satellite systems.(16)
13 (a) Describe architecture of BLUE TOOTH.(16)
[or]
(b)Explain Channel control sub layer in HIPERLAN.(16)
14 (a) Explain optimization in Mobile IP in detail.(16)
[or]
(b)Explain IPV6 Protocol in detail.(16)
15 (a) Discuss the role of WWW in support for mobility.(16)
[or]
(b) Explain the following:
(i) Indirect TCP. (6)
(ii)Snooping TCP.(6)
(iii)Explain about performance enhancing proxies.(4)
B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2009.
Seventh Semester
Information Technology
IT1402- MOBILE COMPUTING
(Regulation 2004)
Time: Three hours Maximum:100 marks
Answer ALL questions.
PART A- (10 X 2= 20 Marks)
1. Why do Hidden and Exposed terminal problems arise?
2. Differentiate Broadcast from Multicast.
3. Detail the features of MSAT.
4. How can an efficient routing be made in satellite systes?
5. When are tuning frequency and frequency considered?
6. How can you utilize mobile antennas efficiently?
7. Compare various modulation techniques.
8. When it's required to go for GMSK, GFSK and DQPSK?
9. In what functionalities Switches differ from Routers?
10. How and why does I-TCP isolate problems on the wireless link?
PART B - (5 X 16 = 80 Marks)
11. (a) Consider three users and Barker code of six bits each for the users transmitting
the signals, introduce noise and near/far problem while transmitting and reconstruct
the data in the receiving side providing the proper countermeasures for the
complications. (Note: Use CDMA technologies) (Marks 16)
(Or)
(b) (i) Table the frequency bands useed for wireless applications with their ranges,
propagation models and applications. (Marks 6)
(ii) Represent diagrammatically the protocol machines for multiple access with
collision avoidance. (Marks 10)
12. (a) (i) Sketch the data network in your campus. How many hosts are there and
how large is the user population? What is the speed of the access link to the Internet?
How so you gain access to the Internet? How much does home access to the Internet
costs? (Marks 10)
(ii) Why are so many different identifiers/addresses (e.g. MSISDN, TMSI, IMSI)
needed in GSM? Give reasons and distinguish between user- related and system
related identifiers. (Marks 6)
(Or)
(b) (i) Consider a mobile user who is migrating from a place to another place, provide
him a seamless service by satellite system, also sketch the architecture. (Marks 8)
(ii) Discuss the importance of DECT Protocol Layers. (Marks 8)
13. (a) (i) Detail the time- bounded service on top of the standard DCF mechanism
where ad hoc networks cannot use the function. (Marks 8)
(ii) Discuss the PHY frame format of an IEEE 802.11 using the spread spectrum
technique which separates by code. (Marks 8)
(Or)
(b) (i) The channel access control sublayer of HIPERLAN offers a connectionless
data transfer service to the higher MAC layer. Justify the above statement with related
references. (Marks 10)
(ii) Discuss the functionalities and support provided by L2CAP. (Marks 6)
14. (a) Discuss and detail the differences in topology reorganization in DSDV and
DSR routing protocols. (Marks 16)
(Or)
(b) (i) What are the general problems of mobile IP regarding security and support of
quality of service? (Marks 8)
(ii) Name the inefficiencies of mobile IP regarding data forwarding from a
correspondent node to a mobile node. What are optimizations and what additional
problems do they cause? (Marks 8)
15. (a) What are the major difference between WAP 2.0 and WAP 1.x? What
influenced the WAP 2.0 development? (Marks 16)
(Or)
(b) Detail about UTMS Radio Interfaces in Frequency Division Duplex and Time
Division Duplex modes. (Marks 16)
MAY /JUNE 2009
MOBILE COMPUTING.
Part –A
1. Define near /far effect?
2. Give any two application of satellite systems?
3. What are ad-hoc networks?
4. Define handover in WATM?
5. What is meant by Registration lifetime of a packet ?
6. What is meant by tunneling?
7. How does the standard TCP behave when a packet is lost during transmission?
8. Define time – out freezing?
9. Mention the role of transaction layer in WAP?
10. Mention any two messages of WCMP?
Part –B
11. a)Explain in detail:
i)DECT system. [Mark 8]
ii)TETRA system. [Mark 8]
Or
b) i) Discuss LEO,MEO, and GEO satellite systems. [Mark 8]
ii) Discuss Digital Video Broadcasting. [Mark 8]
12. a )Explain in detail:
i)HIPERLAN [Mark 8]
ii) BLUETOOTH [Mark 8]
Or
b) What is meant by WATM? Describe WATM reference model, location management ,
services and QOS. [Mark 16]
13.a) i) Discuss the purpose and application of DHCP. [Mark 8] ii) Explain agent
discovery and registration. [Mark 8]
Or
b) Explain the various routing strategies in mobile ad-hoc networks?
14. a) Explain any 4 classical TCP improvement techniques. [Mark 16]
Or
b) i)Discuss Transaction oriented TCP in detail. [Mark 8]
ii) Discuss TCP over 2.5/3G wireless networks. [Mark 8]
15.a) Discuss the component of WAP arch/- and its application environment. [Mark 16]
Or
b)i)Write short notes on WML script. [Mark 8]
ii) Discuss WTA? [Mark 8]
B.E. / B.Tech DEGREE EXAMINATION, NOVEMBER/DECEMBER 2008
Seventh Semester
Information Technology
IT1402 – MOBILE COMPUTING
(Regulation 2004)
Time: Three hours Maximum: 100 marks
Answer ALL questions.
PART A – (10 x 2=20 marks)
1. Differentiate analog modulation and digital modulation.
2. How are guard spaces realized between users in CDMA?
3. What are the general problems of satellite signals travelling from a satellite to
receiver?
4. Differentiate symmetrical and asymmetrical communication system.
5. What is HIPERLAN?
6. How is mobility restricted using WLANS?
7. What could be quick ‘solutions’ and why don’t they work?
8. What advantages does the use of IPV 6 offer for mobility?
9. Write the advantages and disadvantages of mobile TCP.
10. Define fast retransmit.
PART B – (5 x 16 = 80 marks)
11. (a) Explain in detail about multiplexing.
Or
(b) Explain the following :
(i) MAC
(ii) SDMA.
12. (a) Explain the functional architecture of a GSM system.
Or
(b) Discuss about digital video broadcasting.
13. (a) Explain the concept of blue tooth architecture.
Or
(b) Explain the concept of IEEE 802.11 medium access control layer.
14. (a) Explain the following :
(i) DSDV [Marks 8]
(ii) Ad-hoc DSR. [Marks 8]
Or
(b) Discuss about tunneling and encapsulation mechanism and reverse tunneling.
15. (a) Explain and detail about traditional TCP.
Or
(b) (i) Briefly explain about indirect and snooping TCP. [Marks 8]
(ii) Briefly discuss about WAP.[Marks 8]
B.E/B.Tech. Degree Examination, April/May 2008
Eighth Semester
(Regulation 2004)
Computer Science and Engineering
IT 1402- Mobile Computing
Part-A(10*2=20 marks)
1. Assume a receiver is located 10 km from a 150 W transmitter. The carrier
frequency is 6 GHz and free space propagation is assumed, Gain at
transmitter is 1 dB and Gain at receiver is 1 dB.
(a) Calculate the transmit power in dBW.
(b) Find the power at the receiver in Watts.
2. What limits the number of simultaneous users in a TDM/FDM system compared
to a CDM system ? What happens to the transmission quality of connections
if the load gets higher on the cell ?
3. Consider the handoff procedure in GSM system that is based on relative
signal strength with threshold; that is, a mobile switches from one cell
to another if (a) the signal at the current BS is sufficiently weak (less
than a predefined threshold) and (b) the other signal is stronger than
the two. What are the drawbacks of this scheme, when the threshold is
too low or too high ?
4. State the different types of transport modes and channels used to carry
packets in Digital Audio Broadcasting.
5. In the Distributed Coordination Function(DCF) protocol of IEEE 802.11,
why does a Node wait only SIFS time units (after the last data packet
reception) before sending an ACK, while waiting DIFS time units before
attempting a data transmission ?
6. What are the advantages and problems of forwarding mechanisms in Bluetooth
networks regarding security and power saving ?
7. How can DHCP be used for mobility and support of Mobile IP ?
8. What are the differences between AODV and the standard distance vector
algorithm ? Why are extensions needed ?
9. How and why does I-TCP isolate problems on the wireless link ? What are
the main drawbacks of this solution ?
10.Mention two WAP service providers. Find two cell phones supporting WAP
and identify which WAP version they support.
Part-B(5*16=80 marks)
11. (a) How does frequency reuse enhance cellular network capacity ? Besides
the number of users, what other major factor influences the decision
on cluster size ? A cellular system uses frequency spectrum 1800 MHz
to 1840 MHz for uplink channels and 1860 MHz to 1900 MHz for downlink
channels respectively. Each channel takes 200 KHz and can be shared
by 8 users. Each user needs one uplink and one downlink channel. How
many users can be supported without frequency reuse in this cellular
system ? [16]
(OR)
(b) What is the use of spread spectrum ? Sketch the block diagram of the
Transmitter and Receiver of DSSS. Explain what each block does and
what the signal looks like (in time and/or frequency domains) at each
location in the block diagram with an example.[16]
12. (a) Name the main elements of GSM system architecture and describe their
functions. What are the advantages of specifying not only the radio
interface but also the internal interfaces of the GSM system ?
Explain the inter-BSC,intra-MSC handover process in the GSM system
using typical signals and a message sequence chart. Explain the
decision points and the resource allocation steps,if they exist.[16]
(OR)
(b) What is DAB ? Explain the components,frame format and the protocol
used by DAB to access different formats of data also describe how
DVB is used for data broadcasting and to access high speed internet.
[16]
13. (a) (i) Using IEEE 802.11 (DCF): S1 and S2 send CBR/UDP traffic to the
common destination D. Consider S1,S2 and D all within receive
range of each other when the basic scheme is used (no RTS/CTS):
Describe a collision (what happens before,during and after).What
does the collision probability depend on ? When RTS/CTS is used:
What are the changes to the previous answers ? comment also on
the throughput and fairness. [16]
(OR)
(b) (i) Describe the briefly how collision is avoided in HIPERLAN-1. [8]
(ii)Draw the protocol architecture of Bluetooth and explain briefly
the Base band layer and L2CAP of Bluetooth. [8]
14. (a) Given the network topology below, use the dynamic source routing
algorithm to compute the shortest path from A to all other nodes.
Make sure to show the results of the computation at each step.[16]
7
B --- D
|\ 1/ |
| \ / |
12| /\ |1
| /10\ |
A --- C -------- E
3 1
(OR)
(b) Consider a mobile node MN from network X. The user of MN wishes to
communicate with a corresponding node CN in network Y. The node MN
moves from X to a foreign network A. Describe the sequence of
messages that are required in Mobile IPv4 so that MN and CN can
continue to communicate. Include both the user data messages and the
Mobile IP control messages. Now, consider the case where CN moves to
foreign network B while MN is still in the foreign network A. Can
CN and MN still communicate ? (Does Mobile IP support both endpoints
moving? ) Show the message flow to indicate how it will succeed or
fail in this case. [16]
15. (a) As a transport layer protocol, TCP uses a window mechanism to
exercise flow control over the best effort IP in the internet.
Flow control is exercised by the edge router based on congestion
status encountered in the core routers between teh TCP sender and
TCP receiver.
(i) Describe the operation of the window flow control mechanism. [8]
(ii)ACKs from the TCP receiver are the basis that the TCP sender
uses to adjust the sending window size. Describe and discuss
how ACKs are used for this purpose. [8]
(OR)
(b) Specify the enhancements made to the basic client server architecture
of the web to suit a mobile wireless user ? Briefly discuss the main
goals of WAP. Expain the layers of WAP protocol used to achieve the
following : A client wants to have a shared state with the server
for transferring the content. [16]
DEGREE EXAMINATION
MOBILE COMPUTING
Time : Three Hours Maximum : 100 marks
PART A (10 x 2 = 20 marks)
1. What is a guard space?
2. What is CMDA?
3. List the four possible handover and scenarios in GSM
4. Define inclination angle and elevation angle
5. Give the 802.11 PHY frame format using DSS
6. What are the low power states of a blue tooth device?
7. What is a care of address?
8. What are the routing metrics in wireless adhoc network?
9. What is a wireless Telephony application?
10. List the classes of transaction service of WTP.
PART B (5 x 16 = 80 marks)
11. (a) Discuss in detail the Wireless Transaction Protocol. (16)
(or)
(b) Discuss in detail the Wireless Session Protocol (16)
12. (a) Explain time division multiple access (16)
(or)
(b) (i) Discuss the spread spectrum techniques (10)
(ii) What is Code Division Multiplexing? Explain (6)
13. (a) (i) Discuss in detail localization, calling and handover in GSM (10)
(ii) Explain the types of orbits in satellite system (6)
(or)
(b) (i) Explain the GSM system architecture (12)
(ii)Explain the protocol architecture of DECT (4)
14. (a) Discuss in detail the medium access control mechanism of ICCC 802.11 (16)
(or)
(b) (i) Explain the information bases and networking of adhoc HIPERLAN. (8)
(ii) Discuss MAC layer bluetooth system (8)
15. (a) (i)Describe tunneling and encapsulation in Mobile IP (8)
(ii) Discuss in detail dynamic source routing (8)
(or)
(b) (i) Write short notes on reverse tunneling (4)
(ii) Explain IP packet delivery, agent advertisement, discovery and registration process in
mobile IP (12)
DEGREE EXAMINATION
MOBILE COMPUTING
Time : Three Hours Maximum : 100 marks
PART A- (10x2=20 marks)
1. What is spreading factor?
2. What is polling?
3. Distinguish between soft hand over and hard hand over.
4. Define footprint with respect to satellite systems.
5. State the three phases of the medium access of different competing nodes.
6. What are the power saving mechanisms in Bluetooth?
7. What are the drawbacks of wired networks?
8. Define: Dynamic Source Routing.
9. What is the difference between TCP and UDP?
10. Mention any two salient features of WAP.
PART B- (5x16=80 marks)
11.(a)(i) Discuss in detail the types of Antennas with their radiation patterns.
(ii) Explain Diversity techniques.
OR
(b) Explain Space, Frequency, Code and Time Division multiplexing in detail.
12.(a) Describe Digital Audio Broadcasting.
OR
(b) Explain routing, localization and hand over in satellite systems.
13.(a) Describe the architecture of BLUE TOOTH.
OR
(b) Explain channel control sub layer in HIPERLAN.
14.(a) Explain optimization in Mobile IP in detail.
OR
(b) Explain IPv6 protocol in detail.
15.(a) Discuss the role of WWW in support for mobility.
OR
(b) Explain the following:
(i) Indirect TCP.
(ii) Snooping TCP.
(iii) Explain about performance enhancing proxies.
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