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IEEE 802.11 Overview

IEEE 802.11 Overview. Onno W. Purbo Onno@indo.net.id. Wireless Differences Power management Bandwidth Security addressing. Context. Application. Presentation. Session. Transport. Network. 802.2. LLC. Link. 802.3. 802.4. 802.5. 802.11. MAC. Physical. PHY. OSI. IEEE.

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IEEE 802.11 Overview

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  1. IEEE 802.11 Overview Onno W. Purbo Onno@indo.net.id

  2. Wireless Differences Power management Bandwidth Security addressing Context Application Presentation Session Transport Network 802.2 LLC Link 802.3 802.4 802.5 802.11 MAC Physical PHY OSI IEEE

  3. Logical Link Control Services Upper Layer Upper Layer 802.2 802.2 Unack Connectionless Connectionless Oriented Ack Connectionless 802.11 802.11

  4. Topology BSS AP DS AP BSS Extended Service Set (ESS) Basic Service Set (BSS)

  5. Independent BSS

  6. Extended Service Set

  7. Topology Characteristics • Mobility • No transitions • BSS transition • ESS transition (not guaranteed) • Within ESS • BSSs that are partially overlap • BSSs that are physically disjoint • BSSs that are physically collocated

  8. Service primitives Request Confirm Indication responds Logical Architecture LLC CSMA/CA 2.4GHz 1W 300 meter MAC DSSS FHSS IR

  9. 802.11 services • Station Services • Authentication, deauthentication, privacy (WEP), MSDU delivery. • Disrtibuted System Services • Association, deassociation, distribution, integration, reassociation.

  10. How does a station join a BSS? • Scanning • Passive • Active • Authentication • Association

  11. MAC Details • CSMA/CA (time slot = 20 us) • Distributed Coordination Function (DCF). • Virtual carrier sense (RTS/CTS) • Exponential random backoff algorithm. • Priority Based • Point Coordination Function (PCF). • Segmentation & Reassembly.

  12. Physical – DSSS details • 2Mbps w/DQPSK or 1Mbps w/DBPSK • 14 channels (11 channels for US). • 5 plans – 3 max. non-overlapping channels.

  13. Physical – FHSS details • 1Mbps w/ 2 level GFSK • 79 1Mbps channels (2.402 – 2.480 GHz) • 78 sequences (3 sets of 26) • Minimum hop rate = 2.5 hop/s • Minimum hop distance = 6MHz

  14. 802.11 Future • 802.11a • High data rates 2.4GHz band: 5GHz band: 20 Mbps • 802.11b • High data rates 2.4GHz band: FH 4.5Mbps: DS 25.5Mbps • WPAN • Wearable Devices (30 feet, 1Mbps, 0.5 in3, lower power, low cost).

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