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8/6/2019 IEEE 802.11 NCIT
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WIRELESS NETWORKING
ByPradip Paudyal
8/6/2019 IEEE 802.11 NCIT
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COMPUTERS FOR THE NEXT CENTURY?
Computers are integrated
small, cheap, portable, replaceable - no more separate
devices
Advances in technology
more computing power in smaller devices
flat, lightweight displays with low power
consumption
new user interfaces due to small dimensions
more bandwidth per cubic meter
multiple wireless interfaces: wireless LANs, wireless
WANs, regional wireless telecommunication
networks etc
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MOBILE COMMUNICATION
Aspects of mobility:
user mobility: users communicate (wireless) anytime,anywhere, with anyone
device portability: devices can be connected anytime,
anywhere to the network
The demand for mobile communication creates theneed for integration of wireless networks into existing
fixed networks:
local area networks: standardization of IEEE 802.11,
ETSI (HIPERLAN)
Internet: Mobile IP extension of the internet protocol IP
wide area networks: e.g., internetworking of GSM and
ISDN
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CHARACTERISTICS OF WIRELESS LANS
Advantages very flexible within the reception area
Ad-hoc networks without previous planning possible
(almost) no wiring difficulties (e.g. historic buildings,
firewalls)
more robust against disasters like, e.g., earthquakes, fire -or users pulling a plug...
Disadvantages
typically very low bandwidth compared to wired networks
products have to follow many national restrictions ifworking wireless, it takes a vary long time to establish
global solutions like, e.g., IMT-2000
Interfenece
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TYPICAL APPLICATION: ROAD TRAFFIC
UMTS, WLAN,DAB, GSM,
TETRA, ...
Personal Travel Assistant,PDA, laptop,GSM, UMTS, WLAN,Bluetooth, ...
1.4.1
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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 withGSM
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
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WORLDWIDE WIRELESS SUBSCRIBERS
(PREDICTION)
0
100
200
300
400
500
600
700
1996 1997 1998 1999 2000 2001
Americas
Europe
Japan
others
total
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EARLY HISTORY OF WIRELESS
COMMUNICATION
Many people in history used light for communication
flags...
150 BC smoke signals for communication;
(Greece)
1794, optical telegraph
Here electromagnetic waves areof 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 todays University of Karlsruhe)
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DEVELOPMENT OF WIRELESS NETWORK
First Generation Wireless Network
Based on analog technology
FM modulation
E.g. Advanced mobile phone service (AMPS),
Cordless system
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EXAMPLE OF CELLULAR NETWORK
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DEVELOPMENT OF WIRELESS NETWORK
Second Generation Wireless System
Digital modulation and advanced call processingcapabilities
E.g. Global System for Mobile (GSM), Digital
European Cordless Telephone (DECT)
Introduction of BSC
Voice and data services
Mobile assisted hand-off (MAHO)
Third Generation Wireless System
Wide range of application and universal access
Voice, data and video communication
Use of Broadband Integrated Service Digital Network
(BISDN)
E.g. IMT 2000, Universal Mobile Telecommunication
System (UMTS)
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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, ...
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DESIGN GOALS FOR WIRELESS LANS
global, seamless operation
low power for battery use
no special permissions or licenses needed to use the
LAN {ISM band, 2.4 GHz}
robust transmission technology easy to use for everyone, simple management
protection of investment in wired networks
security (no one should be able to read my data),
privacy (no one should be able to collect user
profiles), safety (low radiation)
transparency concerning applications and higher
layer protocols.
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COMPARISON: INFRARED VS. RADIO
TRANSMISSION
Infrared
uses IR diodes, diffuse light,multiple reflections (walls,furniture etc.) Direct light incase of LOS
Advantages
simple, cheap, available in
many mobile devices no licenses needed
simple shielding possible
Disadvantages
interference by sunlight, heatsources etc.
low bandwidthExample
IrDA (Infrared DataAssociation) (115 Kbps , 1.152& 4 Mbps),
Radio
typically using the license freeISM band at 2.4 GHz
Advantages
experience from wireless WAN
and mobile phones can be used
coverage of larger areas
possible (radio can penetratewalls, furniture etc.)
Disadvantages
very limited license free
frequency bands
shielding more difficult,interference with other
electrical devices
Example
IEEE802.11, HIPERLAN,
Bluetooth
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COMPARISON: INFRASTRUCTURE VS.AD-HOC
NETWORKS
infrastructurenetwork
ad-hoc network
APAP
AP
wired network
AP: Access Point
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HIDDEN NODE AND EXPOSED NODE PROBLEM
Hidden terminals A sends to B, C cannot receive A
C wants to send to B, C senses a free medium (CS fails)
collision at B, A cannot receive the collision (CD fails)
A is hidden for C
Exposed terminals B sends to A, C wants to send to another terminal (not A or
B) C has to wait, CS signals a medium in use
but A is outside the radio range of C, therefore waiting is notnecessary
C is exposed to B
BA C
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NEAR AND FAR TERMINALS
Terminals A and B send, C receives
signal strength decreases proportional to the square ofthe distance
the signal of terminal B therefore drowns out As signal
C cannot receive A
Also severe problem for CDMA-networks - precise
power control needed!
A B C
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IEEE STANDARD 802.11
mobile terminal
access point
server
fixed terminal
application
TCP
802.11 PHY
802.11 MAC
IP
802.3 MAC
802.3 PHY
application
TCP
802.3 PHY
802.3 MAC
IP
802.11 MAC
802.11 PHY
LLC
infrastructure network
LLC LLC
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802.11 - LAYERS AND FUNCTIONS
MAC
Medium access mechanisms,
fragmentation (Segmentation),encryption
MAC Management
synchronization, roaming,MAC Information Base (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
PMD (Physical MediumDependent)
PLCP (Physical LayerConvergence Protocol)
MAC (Medium Access Control)
LLC (Logical Link Control)
MAC Management
PHY ManagementPHY
D
LC
StationManagement
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RADIO TRANSMISSION
Orthogonal Frequency Division Multiplex (OFDM) a frequency-division multiplexing (FDM) scheme utilized as adigital multi-carrier modulation method
FHSS (Frequency Hopping Spread Spectrum) spreading, despreading
Operating at 1Mbps/2Mbps
DSSS (Direct Sequence Spread Spectrum) DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift
Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK)
chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barkercode)
max. radiated power 1 W (USA), 100 mW (EU), min. 1mW
Infrared 850-950 nm, diffuse light, typ. 10 m range
carrier detection and synchronization.
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802.11 - MAC MANAGEMENT
Synchronization
try to find a LAN, try to stay within a LAN timer.
Beacon.
Power management
sleep-mode without missing a message
periodic sleep, frame buffering, traffic measurements
Association/Re-association
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
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POWER MANAGEMENT
Idea: switch the transceiver off if not needed
States of a station: sleep and awake
Timing Synchronization Function (TSF) stations wake up at the same time
Infrastructure Traffic Indication Map (TIM)
list of unicast receivers transmitted by AP
Delivery Traffic Indication Map (DTIM)
list of broadcast/multicast receivers transmitted by AP
Ad-hoc
Ad-hoc Traffic Indication Map (ATIM) announcement of receivers by stations buffering frames
more complicated - no central AP
collision of ATIMs possible (scalability?)
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802.11 - ROAMING
No or bad connection? Then perform:
Scanning scan the environment, i.e., listen into the medium for beacon
signals or send probes into the medium and wait for ananswer
Re-association Request station sends a request to one or several AP(s)
Re-association Response success: AP has answered, station can now participate
failure: continue scanning
AP accepts Re-association Request signal the new station to the distribution system
the distribution system updates its data base (i.e., locationinformation)
typically, the distribution system now informs the old AP so itcan release resources
Fast roaming802.11r : e.g. for vehicle-to-roadside networks
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FUTURE DEVELOPMENTS
IEEE 802.11a compatible MAC, but now 5 GHz band
transmission rates up to 20 Mbit/s
close cooperation with BRAN (Broadband Radio AccessNetwork; European Standard)
IEEE 802.11b higher data rates at 2.4 GHz
proprietary solutions already offer 10 Mbit/s
IEEE WPAN (Wireless Personal Area Networks) market potential
compatibility low cost/power, small form factor
technical/economic feasibility
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IMPORTANT STANDARDS
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Thank You???????????????