Wlan Ieee 802.11

Wireless LANs IEEE 802.11 1

Wireless LANsIEEE 802.11

Wireless LANs IEEE 802.11 2

Characteristics of wireless LANs

• Advantages1. Very flexible within the reception area

2. Ad-hoc networks without previous planning possible(almost) no wiring difficulties (e.g. historic buildings, firewalls)

3.More robust against disasters like, e.g., earthquakes, fire -or users pulling a plug...

• Disadvantages1. Typically very low bandwidth compared to wired networks (1-10 Mbit/s)

2. Many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11)

3. Products have to follow many national restrictions if working wireless, it takes a very long time to establish global solutions like, e.g.,IMT-2000

Wireless LANs IEEE 802.11 3

Design goals for wireless LANs

• Global, seamless operation• Low power for battery use • No special permissions or licenses needed to use the LAN • Robust transmission technology• Simplified spontaneous cooperation at meetings • Easy to use for everyone, simple management • Protection of investment in wired networks • Security (no one should be able to read my data), privacy (no one

should be able to collect user profiles), safety (low radiation)• Transparency concerning applications and higher layer protocol’s, but

also location awareness if necessary

Wireless LANs IEEE 802.11 4

Comparison: infrared vs. radio transmission

Infrared RadioUses IR diodes, diffuse light, multiple reflections (walls, furniture etc.)

Advantages1. Simple, cheap, available in many mobile devices2. No licenses needed3. Simple shielding possible

Disadvantages1. Interference by sunlight, heat sources etc.2. Many things shield or absorb IR light 3. Low bandwidth

ExampleIrDA (Infrared Data Association) interface available everywhere

Typically using the license free ISM band at 2.4 GHz

Advantages1. Experience from wireless WAN and mobile

phones can be used 2. Coverage of larger areas possible (radio can

penetrate walls, furniture etc.)

Disadvantages1.Very limited license free frequency bands2. Shielding more difficult, interference with other electrical devices

ExampleWaveLAN, HIPERLAN, Bluetooth

Wireless LANs IEEE 802.11 5

Comparison Infrastructure v/s Ad-hoc networks

Wireless LANs IEEE 802.11 6

802.11 -Architecture of an infrastructure network

Wireless LANs IEEE 802.11 7

802.11 -Architecture of an ad-hoc network

Wireless LANs IEEE 802.11 8

IEEE Standard 802.11

Wireless LANs IEEE 802.11 9

802.11- Layers and Functions

Wireless LANs IEEE 802.11 10

802.11- Physical Layer

Wireless LANs IEEE 802.11 11

DSSS PHY packet format

Wireless LANs IEEE 802.11 12

802.11 – MAC layer I - DFWMAC

Wireless LANs IEEE 802.11 13

802.11 – MAC layer II

Wireless LANs IEEE 802.11 14

802.11 – CSMA/CA access method I

Wireless LANs IEEE 802.11 15

802.11 – competing stations

Wireless LANs IEEE 802.11 16

802.11 – CSMA/CA access method II

Wireless LANs IEEE 802.11 17

802.11 – Frame Format

Wireless LANs IEEE 802.11 18

MAC address format

Wireless LANs IEEE 802.11 19

802.11 – MAC management

Wireless LANs IEEE 802.11 20

Synchronization using a Beacon (infrastructure)

Wireless LANs IEEE 802.11 21

Synchronization using a Beacon (ad-hoc)

Wireless LANs IEEE 802.11 22

802.11 - Roaming

Wireless LANs IEEE 802.11 23

WLAN: IEEE 802.11b

Wireless LANs IEEE 802.11 24

IEEE 802.11b – PHY frame formats

Wireless LANs IEEE 802.11 25

Channel selection (non-overlapping)