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WLAN 802.11b 802.11a

WLAN 802.11b 802.11a. Johan Montelius johan@jmt2.com. IEEE 802. The IEEE link layer standards: 802.3 Ethernet 802.5 Token Ring 802.11 Wireless LAN 802.1 5 Bluetooth. 802.11. 802.11 1 and 2 Mbps on the 2.4 GHz band FHSS, DSSS, IrDA 802.11b DSSS, upgrade to 5.5 and 11 Mbps

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WLAN 802.11b 802.11a

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  1. WLAN802.11b 802.11a Johan Monteliusjohan@jmt2.com

  2. IEEE 802 • The IEEE link layer standards: • 802.3 Ethernet • 802.5 Token Ring • 802.11 Wireless LAN • 802.15 Bluetooth

  3. 802.11 • 802.11 • 1 and 2 Mbps on the 2.4 GHz band • FHSS, DSSS, IrDA • 802.11b • DSSS, upgrade to 5.5 and 11 Mbps • 802.11a • the 5 GHz band • up to 54 Mbps • OFDM, up to 64-QAM • 802.11h • 11a with power control, frequency selection

  4. WLAN vs LAN- what’s the difference Ethernet hub/switch

  5. WLAN vs LAN- what’s the difference WLAN AP WLAN AP ESS BSS BSS

  6. WLAN vs LAN- what’s the difference • Identification • The mobile station must be able to identify the right AP- • Registration • The AP must know which mobile stations it should serve. • Collision Avoidance • it’s hardto do collisiondetection • Security • How do we protect our network?

  7. 802.11b • Physical layer • MAC layer • Power saving • Encryption

  8. 802.11b Spectrum • ISM band • 2.4 GHz • total 83 MHz • Direct sequence spread spectrum • Carriers • 14 carriers (11 US, 13Europe) • bandwidth per carrier 22 MHz

  9. 802.11b Modulation • 1 Mbps • BPSK 11 Mcps • Barker spreading sequence 11 chips wide • 2 Mbps • QPSK 22 Mcps • Barker spreading sequence 11 chips wide • 5,5 and 11 Mbps • QPSK 11 Mcps • spreading code 8 chips wide, encode 4 or 8 bits

  10. CSMA/CA • Carrier Sense • listen to the media before you send • Multiple Access • you’re not alone • Collision Avoidance • the line should be idle for some time • send a short request, wait for clearance

  11. Why not Collision Detection? AP

  12. Collision AvoidancePhysical Carrier Sense DIFS Data SIFS ACK DIFS Backoff Data

  13. Collision AvoidanceVirtual Carrier Sense DIFS RTS CTS SIFS Data Reserved SIFS ACK

  14. Go to sleep if you can • All mobile stations are synchronized by the AP. • Mobile stations can enter doze mode. • The AP will buffer incoming data for stations in doze mode. • The AP periodically send information about which stations have data waiting. • Mobile stations will poll the AP for data.

  15. It’s not secure! • WEP (wired equivalent privacy): encryption at link level. • Shared key in a BSS • Not secure! • AP should be located in a DMZ.

  16. 802.11a • Same MAC layer as 802.11 • Physical layer • 5 GHz band • Orthogonal Frequency Division Multiplexing • Each carrier 20 MHz wide • up to 54 Mbps raw data rate • Forward Error Correction • increase throughput for low signal levels

  17. 5 GHz in the US • 5150 – 5250 MHz • < 40 mW • 5250 – 5350 MHz • < 200 mW • 5725 – 5825 MHz • < 800 mW

  18. 5 GHz In Europe • Hiperlan 1 • 5150 – 5250 MHz • < 200 mW • Indoor only • Hiperlan 2 • 5150 – 5350 and 5470 –5727 MHz • < 1W • Transmit power Control • Dynamic Frequency Selection

  19. 802.11a in Europe • 5150 – 5250 (5150-5250/5125-5135 MHz in the US) • < 200 mW (50/250 mW in the US) • indoor usage • seller should • if possible limit the device • inform the user about limitations • … in reality • same stuff, software controlled, it’s up to you

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