802.11802.11Presented by Hampton SmithPresented by Hampton Smith

802.11802.11

An IEEE (Institute for Electrical and An IEEE (Institute for Electrical and Electronics Engineers) protocol ratified in Electronics Engineers) protocol ratified in 1997 which defines a standard for wireless 1997 which defines a standard for wireless connectivity.connectivity.

Now known as 802.11 Legacy.Now known as 802.11 Legacy. Applies to the Physical and Media Access Applies to the Physical and Media Access

Control layers.Control layers.

802.11 Legacy802.11 Legacy

Allowed for a 1-2 Mb/s data rateAllowed for a 1-2 Mb/s data rate 3 channels, 2.4 GHz (ISM)3 channels, 2.4 GHz (ISM) CSMA/CA, with a random backoffCSMA/CA, with a random backoff SecuritySecurity

RC4 EncryptionRC4 Encryption Authentication through a list or a shared Authentication through a list or a shared

private keyprivate key

802.11 Legacy802.11 Legacy

TopologiesTopologies Ad hoc (on the fly)Ad hoc (on the fly) InfrastructureInfrastructure

Data Transmission Types:Data Transmission Types: Direct Sequence Spread Spectrum (DSSS)Direct Sequence Spread Spectrum (DSSS) Frequency Hopping Spread Spectrum (FHSS)Frequency Hopping Spread Spectrum (FHSS) Infrared SpectrumInfrared Spectrum

DSSS vs FRSSDSSS vs FRSS

Both use Spread SpectrumBoth use Spread Spectrum Spread Spectrum means all devices Spread Spectrum means all devices

transmit within the same bandwidth, transmit within the same bandwidth, devices don’t have assigned frequencies.devices don’t have assigned frequencies.

DSSS vs FHSSDSSS vs FHSS

DSSSDSSS Reduces peak amplitudeReduces peak amplitude Maintains total powerMaintains total power Data encoded using Data encoded using

“clipping bit” and “clipping bit” and transferred at an increased transferred at an increased data rate over multiple data rate over multiple frequenciesfrequencies

Resistant to feedback and Resistant to feedback and temporary noise temporary noise generatorsgenerators

FHSSFHSS Maintains peak amplitudeMaintains peak amplitude ““Hops” from frequency to Hops” from frequency to

frequency many times per frequency many times per second.second.

Avoids feedback by not Avoids feedback by not transmitting on any one transmitting on any one frequency for longfrequency for long

Data TransmissionData Transmission Sender sends RTS Sender sends RTS

(ready to send)(ready to send) Contains information about Contains information about

size of data and the sendersize of data and the sender Receiver sends CTS Receiver sends CTS

(clear to send)(clear to send) Sender sends packetSender sends packet Packet verified through Packet verified through

CRCCRC Receiver sends ACK Receiver sends ACK

(acknowledgement)(acknowledgement) This avoids the “hidden This avoids the “hidden

node problem.”node problem.”

A

B

X

TopologiesTopologies

Ad hocAd hoc Uses Spokesman Election Algorithm (SEA) to Uses Spokesman Election Algorithm (SEA) to

determine Master and Slavesdetermine Master and Slaves Nodes communicate directlyNodes communicate directly

InfrastructureInfrastructure Nodes communicate through an Access PointNodes communicate through an Access Point Access Point relays messages between Access Point relays messages between

nodes and between the nodes and the nodes and between the nodes and the outsideoutside

802.11b802.11b

Eliminates FHSS optionEliminates FHSS option Boosts data rate to a nominal 11 Mb/s Boosts data rate to a nominal 11 Mb/s

(practically about 5 Mb/s)(practically about 5 Mb/s) Does this through voodooDoes this through voodoo

802.11a802.11a

Comes after 802.11b. Go figure.Comes after 802.11b. Go figure. Increases theoretical data rate to 54 Mb/s Increases theoretical data rate to 54 Mb/s

(practical: 27 Mb/s)(practical: 27 Mb/s) Operates on 5 GHz license free bandOperates on 5 GHz license free band

Limited range (about half of 802.11b)Limited range (about half of 802.11b) Incompatible with 802.11b and 802.11 legacy.Incompatible with 802.11b and 802.11 legacy.

Most held out for 802.11g, which was Most held out for 802.11g, which was already in the works.already in the works.

802.11g802.11g

Same transfer as 802.11a (nominal 54 Same transfer as 802.11a (nominal 54 Mb/s, practical 27 Mb/s).Mb/s, practical 27 Mb/s).

Operated on original 2.4 GHz spectrumOperated on original 2.4 GHz spectrum Same range as 802.11bSame range as 802.11b Compatible with 802.11b and 802.11 Compatible with 802.11b and 802.11

legacy technologies.legacy technologies. Best of both worlds option.Best of both worlds option.

SecuritySecurity

RC4 older code, still checked out.RC4 older code, still checked out. Several studies determined that wireless Several studies determined that wireless

was woefully less secure than wired was woefully less secure than wired counterpart.counterpart.

Drafts of 802.11i, but not ratified until Drafts of 802.11i, but not ratified until 2004.2004.

WPA (Wi-Fi (Wireless Fidelity) Protected WPA (Wi-Fi (Wireless Fidelity) Protected Access) Organization.Access) Organization.

Problems with 802.11Problems with 802.11

Limited range, commercial and industrial Limited range, commercial and industrial implementations need repeaters and access implementations need repeaters and access points in many places.points in many places.

Industrial applications use lots of metal and Industrial applications use lots of metal and electric equipment which can reflect, nullify, electric equipment which can reflect, nullify, distort, and broadcast its own signals.distort, and broadcast its own signals.

SecuritySecurity 2.4 GHz band not unlicensed everywhere (Italy, 2.4 GHz band not unlicensed everywhere (Italy,

for example)for example)

Further ReadingFurther Reading

http://standards.ieee.org/getieee802/802.1http://standards.ieee.org/getieee802/802.11.html1.html (Google search “IEEE get wireless 802.11”)(Google search “IEEE get wireless 802.11”)

http://www.computer.org/students/looking/http://www.computer.org/students/looking/summer97/ieee802.htmsummer97/ieee802.htm (Google search “IEEE 802.11 short tutorial”)(Google search “IEEE 802.11 short tutorial”)