wlan ieee 802.11
DESCRIPTION
WlanTRANSCRIPT
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)