wireless lans by armaghan khan fakhruddin mahmood sadiq hasan

Wireless LANsWireless LANs

ByByArmaghan KhanArmaghan Khan

Fakhruddin MahmoodFakhruddin MahmoodSadiq HasanSadiq Hasan

AgendaAgenda

1.1. IntroductionIntroduction

2.2. How Wireless LANs Work?How Wireless LANs Work?

3.3. Technologies InvolvedTechnologies Involved

4.4. StandardsStandards

5.5. Advantages/DisadvantagesAdvantages/Disadvantages

6.6. SummarySummary

How WLANs WorkHow WLANs Work

WLANs Consist of 3 ComponentsWLANs Consist of 3 Components::11 ) )Wired NetworkWired Network

22 ) )Access PointAccess Point

translates between wired LAN and wireless translates between wired LAN and wireless

LANLAN

33 ) )Wireless-LAN Adapters like PC cardsWireless-LAN Adapters like PC cards

Used by end users to access the WLANUsed by end users to access the WLAN

How WLANs Work How WLANs Work (Cont)(Cont)

How WLANs Work How WLANs Work (Cont)(Cont)

Different Access PointsDifferent Access Points

Wireless LANs Wireless LANs TechnologyTechnology

There are 3 different types of There are 3 different types of wireless technologieswireless technologies

Infrared Wireless LANsInfrared Wireless LANs Spread Spectrum LANsSpread Spectrum LANs Narrowband Microwave LANsNarrowband Microwave LANs

Infrared LANsInfrared LANs

There are 3 types of Infrared There are 3 types of Infrared transmission techniquestransmission techniques

1.1. Directed Beam Infrared Directed Beam Infrared

2.2. OmnidirectionalOmnidirectional

3.3. DiffusedDiffused


Directed BeamDirected Beam1.1. Directed IR beams are used to Directed IR beams are used to

create point to point links.create point to point links.2.2. A focussed IR beam can have a A focussed IR beam can have a

range of several kilometers.range of several kilometers.3.3. Can be used for cross building Can be used for cross building

interconnection or for indoor interconnection or for indoor interconnection of LANsinterconnection of LANs


OmnidirectionalOmnidirectional A single base station which is within A single base station which is within

the line of sight of all wireless stations the line of sight of all wireless stations on the LAN.on the LAN.

Mounted on the ceilingMounted on the ceiling It acts as a multiple repeater and It acts as a multiple repeater and

broadcasts a omnidirectional beam.broadcasts a omnidirectional beam. The wireless stations transmit a The wireless stations transmit a

directional beam aimed at the ceiling directional beam aimed at the ceiling base unitbase unit


DiffusedDiffused All the IR transmitters are All the IR transmitters are

focussed at a point on the focussed at a point on the reflecting ceiling.reflecting ceiling.

IR radiations striking the ceiling IR radiations striking the ceiling is reradaited omnidirectionally is reradaited omnidirectionally and picked up by all the and picked up by all the receivers in the area.receivers in the area.


AdvantagesAdvantages1.1. Virtually unlimited bandwidth.Virtually unlimited bandwidth.2.2. Unregulated Spectrum.Unregulated Spectrum.3.3. IR light is diffusely reflected by light-colored IR light is diffusely reflected by light-colored

objects. Can use this property to provide objects. Can use this property to provide coverage in presence of obstacles.coverage in presence of obstacles.

4.4. Does not penetrate walls or other opaque Does not penetrate walls or other opaque objects.objects.

5.5. Easy to secureEasy to secure6.6. Separate networks can operate without Separate networks can operate without

interferenceinterference


DisadvantagesDisadvantages1.1. Interference from background Interference from background

radiation from sunlight. radiation from sunlight.

2.2. Power restrictions due to eye safety.Power restrictions due to eye safety.

3.3. Ambient radiation appears as noise in Ambient radiation appears as noise in an infrared receiver.an infrared receiver.

4.4. Transmitters of higher power Transmitters of higher power required.required.

Spread Spectrum LANsSpread Spectrum LANs

1.1. Spread data transmission across the Spread data transmission across the available frequency band in excess of available frequency band in excess of minimum bandwidth required to send minimum bandwidth required to send information.information.

2.2. Makes it resistant to noise, Makes it resistant to noise, interference, eavesdropping.interference, eavesdropping.

3.3. Used with wireless LANs and other Used with wireless LANs and other personal digital communication personal digital communication devices such as digital cellular phones.devices such as digital cellular phones.


Two of the most popular types of Two of the most popular types of transmission using Spread transmission using Spread Spectrum Analysis are:Spectrum Analysis are:

1.1. Direct Sequence Spread Direct Sequence Spread Spectrum (DSSS)Spectrum (DSSS)

2.2. Frequency Hopping Spread Frequency Hopping Spread Spectrum (FSSS)Spectrum (FSSS)


Direct Sequence Spread Direct Sequence Spread Spectrum(DSSS)Spectrum(DSSS)::

1.1. Most widely recognized form of Spread Most widely recognized form of Spread Spectrum.Spectrum.

2.2. Converts an incoming data bit stream into a Converts an incoming data bit stream into a symbol stream.symbol stream.

3.3. Each symbol represents a group of one or more Each symbol represents a group of one or more bits.bits.

4.4. Using QPKS techniques it multiplies each Using QPKS techniques it multiplies each symbol with a noise like code called symbol with a noise like code called pseudorandom noise sequence. pseudorandom noise sequence.

5.5. Multiplication artificially increases used Multiplication artificially increases used bandwidth based on the length of the chip bandwidth based on the length of the chip sequence.sequence.


Frequency Hopping Spread Frequency Hopping Spread Spectrum(FHSS)Spectrum(FHSS)

1.1. Hops from narrow band to narrow band Hops from narrow band to narrow band within a wide band.within a wide band.

2.2. The hopping pattern or sequence appears The hopping pattern or sequence appears random but is actually a periodic sequence random but is actually a periodic sequence tracked by sender and receiver.tracked by sender and receiver.

3.3. Can be susceptible to noise during any one Can be susceptible to noise during any one hop but can achieve transmissions during hop but can achieve transmissions during other hops within the wideband.other hops within the wideband.


AdvantagesAdvantages1.1. Has the ability to eliminate or alleviate the Has the ability to eliminate or alleviate the

effect of multipath interference.effect of multipath interference.

2.2. Can share the same frequency band Can share the same frequency band (overlay) with other users.(overlay) with other users.

3.3. Provides privacy due to unknown random Provides privacy due to unknown random codes.codes.

4.4. Involves low power spectral density since Involves low power spectral density since signal is spread over a large frequency signal is spread over a large frequency bandband. .


DisadvantagesDisadvantages

1.1. The bandwidth is inefficientThe bandwidth is inefficient

2.2. The implementation of the The implementation of the Spread Spectrum LANs is Spread Spectrum LANs is somewhat complex.somewhat complex.

Narrowband Narrowband Microwave LANsMicrowave LANs

There are basically two types of There are basically two types of Narrowband Microwave LANsNarrowband Microwave LANs

Licensed Narrowband RFLicensed Narrowband RF Unlicensed Narrowband RF Unlicensed Narrowband RF

Narrowband Narrowband Microwave LANsMicrowave LANsLicensed Narrowband RFLicensed Narrowband RF1.1. Licensed within specific geographic Licensed within specific geographic

areas to avoid potential interference.areas to avoid potential interference.2.2. Motorola - 600 licenses in 18-GHz rangeMotorola - 600 licenses in 18-GHz range Covers all metropolitan areasCovers all metropolitan areas Due to licensing, independent LANs in Due to licensing, independent LANs in

nearby locations don’t interferenearby locations don’t interfere Encrypted transmissions prevent Encrypted transmissions prevent

eavesdroppingeavesdropping

Guarantees interference free communicationGuarantees interference free communication

Narrowband Narrowband Microwave LANsMicrowave LANs

Unlicensed Narrowband RFUnlicensed Narrowband RF

1.1. RadioLAN introduced narrowband RadioLAN introduced narrowband wireless LAN in 1995.wireless LAN in 1995.

2.2. Uses unlicensed ISM spectrumUses unlicensed ISM spectrum

3.3. Operates at 10 Mbps in the 5.8-Operates at 10 Mbps in the 5.8-GHz bandGHz band

4.4. Range = 50 m to 100 mRange = 50 m to 100 m

WLAN Standards: The WLAN Standards: The IEEE 802.11IEEE 802.11 Original IEEE 802.11Original IEEE 802.11 AmmendmentsAmmendments

– 802.11a802.11a– 802.11b802.11b– 802.11g802.11g– 802.11n802.11n

802.11 Architecture802.11 Architecture

Original IEEE 802.11 Original IEEE 802.11 (WiFi)(WiFi)

Formed in 1990Formed in 1990 Operates in 2.4 GHz bandOperates in 2.4 GHz band Data rates of 1 & 2 MbpsData rates of 1 & 2 Mbps 3 different technologies 3 different technologies

– Frequency Hopping Spread Spectrum Frequency Hopping Spread Spectrum (FHSS) (FHSS)

– Direct Sequence Spread Spectrum Direct Sequence Spread Spectrum (DSSS)(DSSS)

– Infrared Infrared

IEEE 802.11 IEEE 802.11 Ammendments: Ammendments: 802.11a802.11a Ratified in 1999 Ratified in 1999 uses Orthogonal Frequency uses Orthogonal Frequency

Division Multiplexing (OFDM)Division Multiplexing (OFDM) Data rates of up to 54 MbpsData rates of up to 54 Mbps Operates in 5 GHz band [free of Operates in 5 GHz band [free of

interference]interference] Reduced indoor range from 50 to Reduced indoor range from 50 to

30m30m

IEEE 802.11 IEEE 802.11 Ammendments: Ammendments: 802.11b802.11b Ratified in 1999 Ratified in 1999 Extension of original 802.11Extension of original 802.11 uses a technique called uses a technique called

Complementary Code Keying Complementary Code Keying (CCK)(CCK)

Improved data rate of 11 MbpsImproved data rate of 11 Mbps

IEEE 802.11 IEEE 802.11 Ammendments: Ammendments: 802.11g802.11g Ratified in 2003 Ratified in 2003 Operates in 2.4 GHz band Operates in 2.4 GHz band Uses Orthogonal Frequency Uses Orthogonal Frequency

Division Multiplexing (OFDM) like Division Multiplexing (OFDM) like 802.11a802.11a

Data rates of up to 54 Mbps Data rates of up to 54 Mbps

IEEE 802.11 IEEE 802.11 Ammendments: Ammendments: 802.11n802.11n Announced in 2004Announced in 2004 Expected in 2007Expected in 2007 Will use Multiple-Input Multiple-Will use Multiple-Input Multiple-

Output (MIMO) technology Output (MIMO) technology Proposed data rate of 540 Mbps!!!Proposed data rate of 540 Mbps!!!

IEEE 802.11 IEEE 802.11 ArchitectureArchitecture

ComponentsComponents– Basic Service Set (BSS)Basic Service Set (BSS)– Access Point (AP)Access Point (AP)– Distribution System (DS) Distribution System (DS) – Extended Service Set (ESS)Extended Service Set (ESS)– Portal Portal

IEEE 802.11 IEEE 802.11 ArchitectureArchitecture

LAN

PORTAL

Other standardsOther standards

HiperLAN developed by European HiperLAN developed by European Telecommunications Standards Telecommunications Standards Institute (ETSI)Institute (ETSI)

Also HiperLAN IIAlso HiperLAN II OpenAirOpenAir HomeRF HomeRF SWAPSWAP

Developed by private corporations

Advantages of Advantages of WLANsWLANs

1) 1) Long-Term Cost Savings Long-Term Cost Savings

a)a) Eliminating the direct costs of cablingEliminating the direct costs of cabling

b) b) Effects of reorganizationEffects of reorganization

2) 2) Reduced Installation Time Reduced Installation Time a) a) Eliminating the time needed for cablingEliminating the time needed for cabling

b) b) reach places that cannot be reached by reach places that cannot be reached by

wireswires

Advantages of WLANsAdvantages of WLANs (Cont)(Cont)

33 ( (MobilityMobility

- - users can physically move while using the users can physically move while using the

LANLAN - - Examples: healthcare workers, policemenExamples: healthcare workers, policemen

44 ) )ScalabilityScalability a) a) Designed at any size, then can be Designed at any size, then can be

expandedexpanded

b) b) connect several buildingsconnect several buildings

Advantages of WLANsAdvantages of WLANs (Cont)(Cont)

55 ) )Easy access to the Internet inEasy access to the Internet in

public placespublic places

--Examples: conference rooms ,hotelsExamples: conference rooms ,hotels..

Disadvantages of Disadvantages of WLANsWLANs

11((InterferenceInterference Same bandwidth like mobiles & microwave Same bandwidth like mobiles & microwave

ovensovens..

22 ( (SpeedSpeed much less speed than that offered with wired LANmuch less speed than that offered with wired LAN

33 ( (HealthHealth Same health concerns as cell phonesSame health concerns as cell phones

44 ( (SecuritySecurity any neighbor may be able to access to internal any neighbor may be able to access to internal

network resourcesnetwork resources

wireless lans by armaghan khan fakhruddin mahmood sadiq hasan

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