Introduction Tow Lans

7/29/2019 Introduction Tow Lans

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Copyright AirTight Neworks

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



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



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



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



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



WLAN Network Architecture(2/2)

ESS: a set of BSSs interconnected by a distribution system (DS)

Local Area Network (e.g .Ethernet)



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



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



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

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Introduction Tow Lans