IEEE 802.11
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IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specifications for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. The goal of 802.11 is to provide simple, robust, and affordable wireless connectivity along with time-bound and asynchronous services. It uses either spread spectrum or infrared signaling techniques. The standard defines the MAC sublayer and three physical layer types: infrared, frequency-hopping spread spectrum (FHSS), and direct-sequence spread spectrum (DSSS). It supports infrastructure-based and ad-hoc network configurations.
IEEE 802.11
- 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 Management DLC LLC MAC MAC Management PLCP PHY PMD PHY Management Detailed 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).
Editor's Notes
- #10: Data link contro