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Introduction to WLANs
AirTight Networks, Inc.
339 N. Bernardo Ave, #200Mountain View, CA 94043
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Presentation Outline
WLAN Fundamentals Technology Positioning
Technical Basics
Typical Applications
Standards
Key Issues in WLAN deployments
Security
Network planning and management
QoS
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What is WLAN
WLAN (Wireless LAN or also called Wi-Fi) is a wirelessversion of the Ethernet
Suitable for indoor/local wireless coverage
Typical range under 40 meters
Range highly dependent on the space layoutOptimized for packet based communication, e.g.,
Internet Protocol (IP)
Transmission speed
Upto 11 Mbps for 802.11b Upto 54 Mbps for 802.11a or 802.11g
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WLAN is Open Technology
Anyone can build and sell WLAN equipment as longas
Power radiation regulations are obeyed
Interoperability standards are mature and openly
available (IEEE 802.11 and WiFi Alliance)No need for spectrum license to operate WLAN
WLAN operates in 2.4 GHz (b, g) or 5 GHz (a) unlicensed
bands
Openness of technology is a blessing as well as aliability!
Compare Internet with telephone (fixed and mobile)
networks
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WLAN Already a Commodity
Variety of WLAN equipment is already available inthe marketplace
Access point, PCIMCA cards for laptops, bridges for
desktops
WLAN built in laptops, PDAs, Mobile phones
WLAN chipsets
WLAN related softwares
WLAN available for enterprise, domestic and public
applications
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WLAN Market Projections areExplosive
0
1
2
3
4
5
$-
bil
2001 2002 2003 2004 2005
Forecast Sales of Wi-Fi Equipment
(Source: InfoTech Trends)
Source: Pyramid Research
Worldwide WLAN Infrastructure
Shipments (Source: Gartner)
0
1
2
3
4
5
6
7
2001
2002
2003
2004
2005
2006
2007
MillionsofUnit
WLAN Growth Drivers
Convenience & Flexibility
Productivity Gains
Low Cost
Embedded WLAN
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Typical WLAN Applications
Wireless OfficeWireless Internet connectivity, VoIP
Wireless Home
Laptops, entertainment systems, appliances
Public hot-spotsWireless Internet connectivity in malls, coffee shops,
libraries, airports
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WLAN Technical PhysicalLayer
Transmission Method Spread spectrum (DSSS) for 11 Mbps 802.11b in 2.4 GHz
band
Orthogonal frequency division multiplexing (OFDM) for 54
Mbps 802.11g in 5 GHz band
OFDM for 54 Mbps 802.11a in 5 GHz band
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MAC Layer
Manages access of multiple wireless stations toshared wireless medium CSMA/CA (Carrier Sense Multiple Access with Collision
Avoidance)
Assists in security over the wireless link Encrypt all wireless communication
Authenticate clients before granting access
Assists in association management Binding client identity of access point
Portability, mobility
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Operation of CSMA/CA Protocol
Only one device can transmit at a time, else packet collision occurs
Immediate access when medium is sensed free >= DIFS period
When medium is not free, defer until the end of current frame + DIFS period
Begin backoff procedure Choose a random number in (0, CWindow)
Sense medium to determine if there is activity during each slot
Decrement backoff time by one slot if no activity is detected during that slot
Suspend backoff procedure if medium is determined to be busy at anytime during abackoff slot
Resume backoff precedure after the end of current frame transmission
A
DIFS
Frame
B
FrameC
D
DIFS
defer
defer
defer
CWindow
DIFS
Frame
CWindow
DIFS
Frame
DIFS
Frame
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WLAN Network Architecture(1/2)
Basic Service Set (BSS): a set of stations which communicate
with one another
Ad hoc network
Only direct communicationpossible
No relay function
Infrastructure Mode
Stations communicate with AP
AP provides connection to wired network
(e.g. Ethernet)
Stations not allowed to communicate directly
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WLAN Network Architecture(2/2)
ESS: a set of BSSs interconnected by a distribution system (DS)
Local Area Network (e.g .Ethernet)
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Typical Connection Procedure
1) Authentication exchange
2) Association exchange
3) Encrypted data exchange
Client proves its
identity to AP
Client binds its
identity to AP
Data communication
may continue
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Encryption on Wireless Link
Initial attempts to provide encryption on wireless link were hugefailure!
WEP (Wireless Equivalent Privacy) turned out to becryptographically weak
WEP is a stream cipher
Slowed down adoption of WLAN, especially in enterpriseapplications
WPA (Wireless Protected Access) was created as enhancement
Backward compatible with WEP-based WLAN hardware
Cryptographically much stronger than WEP
Also called TKIP (Temporal Key Integrity Protocol)
Future is AES (Advanced Encryption Standard) Cryptographically strong
Needs specialized hardware
AES is block cipher
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WLAN Standards
IEEE makes WLAN standardsIEEE 802.11 MAC layer
IEEE 802.11i Encryption techniques WPA, AES
Authentication techniques 802.1x
IEEE 802.11e QoS over wireless link
IEEE 802.11f Seamless handoffs between access points
WiFi Alliance drives interoperability of equipment based on IEEE
802.11 standards E.g. WiFi Certified logo