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WIRELESS NETWORKING

ByPradip Paudyal

Ppaudyal@nta.gov.np

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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???????????????