IEEE 802.11 wireless LAN

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WWIIRREELLEESSSS LLAANN
V.Par thipan Assistant Professor ,Saveetha
University

2.  LANs provide connectivity for
interconnecting computing resources at the
local levels of an organization
 Wired LANs
Limitations because of physical, hard-wired
infrastructure
 Wireless LANs provide
Flexibility
Portability
Mobility
Ease of Installation

3.  In response to lacking standards, IEEE
developed the first internationally recognized
wireless LAN standard – IEEE 802.11
 IEEE published 802.11 in 1997, after seven
years of work
 Most prominent specification for WLANs
 Scope of IEEE 802.11 is limited to Physical
and Data Link Layers.

4.  Appliance Interoperability
 Fast Product Development
 Stable Future Migration
 Price Reductions
 The 802.11 standard takes into account
the following significant differences
between wireless and wired LANs:
Power Management
Security
Bandwidth

5. IEEE 802.3
Carrier
Sense
IEEE 802.4
Token
Bus
IEEE 802.5
Token
Ring
IEEE 802.11
Wireless
IEEE 802.2
Logical Link Control (LLC)
PHY
OSI Layer 1
(Physical)
Mac
OSI Layer 2
(Data Link)

6.  Medical Professionals
 Education
 Temporary Situations
 Airlines
 Security Staff
 Emergency Centers

7.  In historical building and small office where
cabling is not economical.
 Supports nomadic access by providing a
wireless link between a LAN hub and mobile
data terminal with an antenna.
 Creation of an adhoc n/ws.
i.e peer to peer network with no centralized
server that is set up temporarily to meet
some immediate need.

8. CM
10 Mbps
Ethernet
switch
UM
Bridge
Or
Router
Server
100 Mbps Ethernet switch
Server

9.  Mostly a wireless Lan will be linked into a wired LAN. This is called LAN
Extension.
 Control Module is wireless LAN acts as an interface to a wired LAN
 If all wireless end systems are within the range of a single control module,
then it is called single cell wireless LAN.
 If multiple control Module are present ,then it is multiple cell wireless LAN.
 CM- control module uses polling or token passing scheme to regulate
access from end systems.
 Hubs or user module(UM), that control number of stations directly without a
wired LAN, can also be a part of wireless LAN

10.  Wireless LAN requirement:-
 throughput – should provide high capacity.
 Number of nodes –should support many data.
 Connectivity of backbone LAN.
 Battery power consumption- use battery powered workstations , so when
not using n/w, can be set to sleep mode to reduce power consumption.
 Transmission robustness and security:
Highly interference prone should provide reliable transfer.
 coallocated network operation –Wireless LAN operating in same area may
face interference.
 License free operation – should provide wireless products without license
for frequency based used.
 Hand off (or) Roaming – mobile station can move from cell to another.
 Dynamic configuration: automated addition or relocation of end systems
without disruption to others.

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AADD--HHOOCC NNEETTWWOORRKK

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IInnffrraassttrruuccttuurree

13.  Access point (AP): A station that provides access
to the DS.
 Basic service set (BSS): A set of stations
controlled by a single AP.
 Distribution system (DS): A system used to
interconnect a set of BSSs to create an ESS.
DS is implementation-independent. It can be a wired
802.3 Ethernet LAN, 802.4 token bus, 802.5 token
ring or another 802.11 medium.
 Extended service set (ESS):Two or more BSS
interconnected by DS
 Portal: Logical entity where 802.11 network
integrates with a non 802.11 network.

14.  Distribution service (DS)
Used to exchange MAC frames from station in
one BSS to station in another BSS
 Integration service
Transfer of data between station on IEEE
802.11 LAN and station on integrated IEEE
802.x LAN

15.  Association
Establishes initial association between station
and AP. Each station must send its identify to
all others through AP
 Re-association
Enables transfer of association from one AP to
another, allowing station to move from one
BSS to another
 Disassociation
Association termination notice from station or
AP

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17.  Authentication
Establishes identity of stations to each other
 De-authentication
Invoked when existing authentication is
terminated
 Privacy
Prevents message contents from being read by
unintended recipient.

18. IEEE 802.11 MMEEDDIIUUMM AACCCCEESSSS
CCOONNTTRROOLL
 MAC layer covers three functional areas:
Reliable data delivery
Access control
Security

19. MMAACC FFRRAAMMEE FFOORRMMAATT
2 2 6 6 6 2 6 0-2312 4
Frame
Control
Duration
ID
Addr 1 Addr 2 Addr 3 Sequence Addr 4
Control
Frame CRC
Body
802.11 MAC Header
Bits: 2 2 4 1 1 1 1 1 1 1 1
Protocol
Version Type SubType To
DS
Retry Pwr
Mgt
More
Data
WEP Order
From More
DS
Frag
Frame Control Field

20. MMAACC LLAAYYEERR FFRRAAMMEESS
 Data Frames
 Control Frames
RTS,CTS,ACK and PS-POLL
 Management Frames
Authentication and De-Authentication
Association, Re-Association, and Disassociation
Beacon and Probe frames

21. IISS WWLLAANN SSEECCUURREE ??
The Parking Lot
attack
Man in the
middle attack
Freely available
tools like Air
Snort, WEP
crack to snoop
into a WLAN

22. PHYSICAL MMEEDDIIAA DDEEFFIINNEEDD BBYY
OORRIIGGIINNAALL 880022..1111 SSTTAANNDDAARRDD
 Frequency-hopping spread spectrum
Operating in 2.4 GHz ISM band
Lower cost, power consumption
Most tolerant to signal interference
 Direct-sequence spread spectrum
Operating in 2.4 GHz ISM band
Supports higher data rates
More range than FH or IR physical layers
 Infrared
Lowest cost
Lowest range compared to spread spectrum
Doesn’t penetrate walls, so no eavesdropping

23. FREQUENCY HHOOPPPPIINNGG SSPPRREEAADD
SSPPEECCTTRRUUMM
 Signal is broadcast over seemingly random series of
radio frequencies
 Signal hops from frequency to frequency at fixed
intervals
 Receiver, hopping between frequencies in
synchronization with transmitter, picks up message
 Advantages
Efficient utilization of available bandwidth
Eavesdropper hear only unintelligible blips
Attempts to jam signal on one frequency succeed only at
knocking out a few bits

24. DIRECT SSEEQQUUEENNCCEE SSPPRREEAADD
SSPPEECCTTRRUUMM
 Each bit in original signal is represented by
multiple bits in the transmitted signal
 Spreading code spreads signal across a
wider frequency band
 DSSS is the only physical layer specified for
the 802.11b specification
802.11a and 802.11b differ in use of chipping
method
802.11a uses 11-bit barker chip
802.11b uses 8-bit complimentary code keying
(CCK) algorithm

25. IEEE 880022..1111AA AANNDD IIEEEEEE
880022..1111BB
 IEEE 802.11a – limited data rate
Makes use of 5-GHz band
Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps
Uses orthogonal frequency division multiplexing (OFDM)
 IEEE 802.11b
802.11b operates in 2.4 GHz band
Provides data rates of 5.5 and 11 Mbps
Complementary code keying (CCK) modulation scheme.
Multiple carrier signals at different frequency sending some of the
bits on each channel.

26. IEEE 802.11 standards :
IEEE 802.11 a
Multipath Effect(Multipath Fading)
is simply a term used to describe the multiple
Paths the radio wave may follow between
transmitter and receiver

27. IEEE 802.11 standards :
IEEE 802.11 a
Orthogonal Frequency Division Multiplexing(OFDM)
OFDM a digital multi-carrier modulation method. A large
number of closely-spaced orthogonal sub-carriers are used to
carry data.
Although the principles and some of the benefits have
been known since the 1960s, OFDM is popular for
wideband communications today by way of low-cost digital
signal processing components that can efficiently calculate
the FFT.

28. IEEE 802.11 standards :
IEEE 802.11 a
Frequency = 5 GHz
Maximum Speed = 54 Mbps
Range = about 35 meters(Varies)
Encoding Scheme = OFDM

29. IEEE 802.11 standards :
IEEE 802.11 b
Frequency = 2.4 GHz (ISM band)
Maximum Speed =11 Mbps
Range = about 38meters(Varies)
Encoding Scheme = DSSS
Modulation Technique= BPSK(1 Mbps),
DQPSK(2 Mbps), CCK(5.5 Mbps,11Mbps)

30. FFUUTTUURREE OOFF WWLLAANN
WLANs move to maturity
Higher Speeds
Improved Security
Seamless end-to-end protocols
Better Error control
Long distances
New vendors
Better interoperability
Global networking