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IEEE 802.11

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    • 1. IEEE 802.11 Presented By: Abhishek Pachisia B.Tech – IT
    • 2. Foreword - 1 • Belong to 802.x LAN standards. • Primary goal – Simple and Robust WLAN – Time bound and Asynchronous services • MAC Layer – Should be able to operate with multiple physical layers (different medium sense & transmission characteristic. • Physical layer. – Infra red & Spread spectrum radio transmission techniques.
    • 3. Foreword - 2 • Additional features of WLAN – Support of power management – Handling of hidden nodes – Ability to operate world wide. • 2.4 GHz ISM band – original standard. – 1 Mbits/s – Mandatory – 2 Mbits/s – Optional.
    • 4. System Architecture - 1 • Basic System Architecture – Infrastructure based – Ad-hoc. • Components – Station (STA) – Access Points (AP) – Basic Service Set (BSS) – Extended Service Set (ESS) – Portal
    • 5. Architecture of an Infrastructure based IEEE 802.11
    • 6. System Architecture - 2 • Stations – Access mechanism to wireless medium – Radio contact to the AP. • BSS – BSSi are connected via Distributed System. • ESS – Form Single network, extends wireless coverage area. – ESSID : Name of network; Separate different network • Portal – Internetworking unit to other LANs.
    • 7. System Architecture - 3 • AP’s support roaming. • Distributed system – Transfer between AP’s. • Infrastructure based network allow ad-hoc network between stations -> IBSS. • IEEE 802.11 does not specify – Routing – Forwarding of data – Exchange of topology Information
    • 8. Architecture of IEEE 802.11 ad-hoc wireless LANs
    • 9. Protocol Architecture - 1 • 802.11 fits seamlessly into 802.x wired networks. • Most common scenario – 802.11 & 802.3 via bridge. • Difference in bandwidth is noticed. • Upper part of logical link layer and data link control layer covers MAC differences.
    • 10. IEEE 802.11 – Protocol architecture and belonging
    • 11. Protocol Architecture - 2 • Physical Layer(PHY) – Physical Layer Convergence Protocol (PLCP) – Physical Medium Dependent sublayer (PMD) • Medium Access Control Layer (MAC) – To access medium. – To fragment user data. – To encrypt. • PLCP – Carrier sense signal (CSS) – Common Service Access Point(SAP) • PMD – Encoding/Decoding Signals.
    • 12. Station ManagementDLC LLC MAC MAC Management PLCPPHY PMD PHY ManagementDetailed IEEE 802.11 protocol architecture and management
    • 13. Physical Layer • Three Layers – Infra red (1) – Radio transmission (2) • Clear Channel Assessment signal (CCA). – MAC mechanism controlling medium access. – Indicates state of medium. • Service Access Point (SAP) • Versions of PHY layer – FHSS – DSSS – Infra red
    • 14. FHSS • Allows coexistence of multiple networks. • Original Standard – 79 hopping channel North America. – 23 hopping channel Japan • Pseudo random hoping pattern. • Standard – GFSK as modulation for FHSS PHY. • 1Mbits/s is mandatory & 2Mbit/s is optional. • MAC data is scrambled using s(z)=z7+z4+1
    • 15. Bits 80 16 12 4 16 Variable Synchronization SFD PLW PSF HEC Payload PLCP Preamble PLCP Header Format of an IEEE 802.11 PHY frames using FHSS
    • 16. DSSS - 1 • Separated by code. • Achieved using 11-chip Barker sequence. • Key characteristics – Robustness against interference – Insensitivity to multipath propagation. • Implementation - Complex than FHSS. • Uses – Differential Binary Phase Shift Keying (DBPSK) – Differential Quadrature Phase Shift Keying (DQPSK)
    • 17. DSSS - 2 • Maximum transmit power – US => 1W – Europe => 100mW EIRP – Japan => 10mW/MHz • Bits are scrambled by s(z)=z7+z4+1 • Two basic parts – PLCP part (Preamble and header) – Payload part.
    • 18. Bits 128 16 8 8 16 16 Variable Synchronization SFD Signal Service Length HEC Payload PLCP Preamble PLCP Header Format of an IEEE 802.11 PHY frame using DSSS
    • 19. Infra red • Uses visible light => 850-950nm. • No line of sight required. • Maximum range =>10m (no interference). • Today no product offer communication based on infra red. • Proprietary products offer up to 4Mbits/s using diffuse infra red light. • Directed infra red communication based on IrDA can be used (IrDA,2002).