mubeen wi fi

8/9/2019 mubeen wi fi

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Wi-Fi


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Wi-Fi (Wireless-Fidelity) is a wirelesstechnology brand owned by the Wi-Fi Alliance

intended to improve the interoperability ofwireless local area network products basedon the IEEE 802.11 standards.

Common applications for Wi-Fi includeInternet, VOIP etc.,

Official Wi-Fi logo


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802.11 and Wi-FiIEEE 802.11 is a set of industry

standards for the operation of wirelessnetworks.

Wi-Fi (Wireless Fidelity) is amarketing term.

Synonymous with 802.11


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802.11: Several Flavors

1999:

802.11b(11/5 Mbits/s)

2001:

802.11a(54/32 Mbits/s)

2003:

802.11g(54/32 Mbits/s)

compatible


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Wi-Fi Access Points A Wi-Fi access point is a blackbox that

connects to the Internet, and also accepts

Wi-Fi connections. The area covered by one or several

interconnected access points is called hotspot.


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WiFi Network Topologies Ad Hoc Network

This is a peer to peer

network.

Infrastructure Network

This network allows to

access various wirednetworks.This requires abase station called

Access Point.


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802.11b The 802.11b standard defines a total of

14 frequency channels.

Channel represents a center frequency.Only 5 MHz separation between centerfrequencies of channels.

21 3 4 5 6 7 8 9 10 11

2.412 2.417 2.422 2.427 2.432 2.437 2.442 2.447 2.452 2.457 2.462

Channel

Center

Frequency

(GHz)

5 MHz


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Ideally, 802.11b supports wireless connectionsbetween an access point and a wireless device at

four possible data rates: 1 Mbps, 2 Mbps, 5.5 Mbps,and 11 Mbps.

Specifically, as terminal travels farther from its AP,the connection will remain intact but connectionspeed decreases (falls back).

11 Mbps

5.5 Mbps2 Mbps


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802.11a 802.11a specification operates at radio frequencies

between 5.15 and 5.825 GHz

The FCC has divided total 300 MHz in this band intothree distinct 100 MHz bands: low, middle, and high,each with different legal maximum power.

Band Channel Max Power

High band 5.725-5.825 GHz 9-12 1000 mW

Middle band 5.25-5.35 GHz 5-8 250 mW

Low band 5.15-5.25 GHz 1-4 50 mW


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Because of high power output, high band used forbuilding-to-building products. Lower two bands

suitable for in-building wireless products. In 802.11a, radio signals are generated using a

method called Orthogonal Frequency DivisionMultiplexing (OFDM).

802.11a (like 11b) has a rate fall back mechanism,i.e., as the distance between the transmitter andreceiver increases, the supported data ratedecreases.


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54 Mbps

48 Mbps

36 Mbps

24 Mbps

12 Mbps

802.11a


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802.11g 802.11g offers throughput of 802.11a with

backward compatibility of 802.11b

802.11g operates in 2.4 GHz band but itdelivers data rates from 6 Mbps to 54 Mbps.

802.11g also uses OFDM but supports

spread-spectrum capabilities if any onecomponent of the system has olderequipment, i.e., 802.11b equipment.


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Wireless Technologies

Up to 54Mbps

Up to 11 Mbps

Up to 54 Mbps

75Mbps, if range is 6 miles

25 to 75 feetindoors

Up to 300 feetindoors

Up to 150 feetindoors

35 miles

5GHz

2.4GHz

2.4GHz

10-66 GHz

802.11a

802.11b

802.11g

802.16 WiMax

SpeedRangeFrequency

Technology


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802.11 MAC Layer 802.11 makes use ofCSMA/CA (Carrier sense

multiple access with collision avoidance)

A CSMA/CD works as (in LAN) : A station desires totransmit, senses the medium, if the medium is busy,then the station will defer its transmission to a latertime, if the medium is sensed free then the station isallowed to transmit.

Two modes of operation are supported by CSMA/CA.


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In the first method, when a stationwants to transmit, it senses the

channel. If the channel is idle, it starts

transmitting else it waits until thechannel is idle.

The second method makes use ofvirtual carrier sensing.


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Virtual Carrier Sense

RTS

CTS

Data

ACK

Source

Access Point

A station willing to transmit sends a short control packet called RTS(Request to Send) which includes source, destination and duration of thefollowing transaction. Then the Access Point will send a response controlpacket, CTS (Clear To Send) which consists the same information.


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Access

Point Laptop

RTS

CTS

Data

ACK


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How WiFi Works? When a station wants to join the Cell, it can

know the synchronization information from

the Access Point in two ways Passive scanning waits to receive

Beacon Frames from the AP

Active scanning transmits the Proberequest to find the AP and waiting for theProbe response from AP


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WLAN DiscoveryOpen WLANs

Access Point continuously transmits

Beacon Frames containing networksSSID.

Closed WLANs Beacon frames do not contain SSID and/or

beacons frames are turned off.

SSID

RESPONSE:SSID

PROBEREQUEST(SSID)

Passive Scanning

Active Scanning

PROBEREQUEST

(ANY)

RESPONSE:SSID

PROBEREQUEST

(ANY)

OPEN

CLOSED

PROBEREQUEST

(ANY)

PROBEREQUEST

(ANY)

{


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Wi-Fi Privacy Problem: Your radio transmissions can be

picked up by anyone.

Access PointAccess PointLaptopLaptop(Wireless PCCard)(Wireless PCCard)

Solution: Encryption


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Wi-Fi privacy is provided by using somekeys called as

Wired EquivalentPrivacy (WEP)

Wi-Fi ProtectedAccess (WPA)


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Wi-Fi Privacy: Observations

38%:WEP

62%:Completelyopen

Source: http://www.worldwidewardrive.org/wwwdstats.html


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Services The services provided by 802.11 are divided in to two

categories as

Distribution Services Station Services

Distribution services relate to managing cellmembership and interacting with stations outside

the cell.In contrast, the station services relate to activity

with in a single cell.


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Distribution Services Association: This service is used by mobile stations

to connect themselves to the base stations.

Disassociation: Either station or the base stationmay use this service before shutting down or leaving.

Reassociation: This process of moving a stationfrom old base station to new base station.

Distribution: This service determines how to route

frames sent to base station. Integration: If a frame needs to be send through a

non-802.11 network with different format, thisservice handles the format translation.


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Station Services There are 4 station services which are intracell.They

are used after association has taken place and are asfollows.

Authentication:

Because wireless communication can easily be sentor received by unauthorized stations, a station mustauthenticate itself before it is permitted to send data.

After a mobile station has been associated by thebase station, the base station sends a challengeframe to see if the mobile knows the secret key(WEP)


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The mobile is supposed to encrypt the challengeframe with the key and send back to the basestation.

If the result is correct then the mobile is enrolled inthe cell.

Authentication Frame

Encrypted Text (using WEP key)

Authentication Frame (Accept/Reject)

Decrypt text using correct WEPkey

Device

NIC


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Deauthentication: When a previouslyauthenticated station wants to leave the network, itis deauthenticated.

Privacy: For information sent over a wireless LAN tobe kept confidential, it must be encrypted.Thisservice manages encryption and decryption.

Data delivery: Finally, data transmission is what itis all about, so this service handles this function.


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ExamplesVirtual Guide inShopping Mall

Virtual Guide in Shopping Mall is an applicationwhich guide the a customer who comes to a big

shopping mall.

As soon as he enters into shopping mall a virtualcharacter comes on his wireless terminal and assistyou through out your shopping


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ExamplesFriendly Job Fair

Friendly Job Fair is a WiFibased application which

allow the job seekers variousinformation such as whichcompanies are participationin job fair what are theirrequirements and what isthe selection process for

various job levels.This alsoprovide you in which stallswhich companies are their.


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Patient MonitoringSystem onTips

This is an application which allows the doctors to

medicate the patients without the help of nurses bygetting their details instantly through their wirelessterminals. A doctor no needs to depend on nurses forthe patient condition. All the details of the patientsare maintained by the server which can be accessedby wireless terminals such as PDA.

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