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Chapter 14. Wireless LANs

Chapter 14. Wireless LANs. IEEE 802.11 Bluetooth. Basic Service Set (BSS). BSS The building block of a wireless LAN BSS with an AP Access Point (AP): central base station BSS without an AP Stand-alone network Cannot send data to other BSSs Ad hoc architecture BSS with an AP

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Chapter 14. Wireless LANs

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  1. Chapter 14. Wireless LANs IEEE 802.11 Bluetooth Data Communications, Kwangwoon University

  2. Basic Service Set (BSS) • BSS • The building block of a wireless LAN • BSS with an AP • Access Point (AP): central base station • BSS without an AP • Stand-alone network • Cannot send data to other BSSs • Ad hoc architecture • BSS with an AP • Called an infrastructure network Data Communications, Kwangwoon University

  3. BSS Data Communications, Kwangwoon University

  4. Extended Service Set (ESS) • BSSs are connected through a distribution system: infrastructure network (usually wired LAN) • Station Types: No-transition, BSS-transition, and ESS-transition mobility Data Communications, Kwangwoon University

  5. MAC Sublayer • Two MAC sublayers: DCF and PCF • DCF uses CSMA/CA as the access method Data Communications, Kwangwoon University

  6. CSMA/CA Flow Chart Data Communications, Kwangwoon University

  7. CSMA/CA and NAV • Network allocation vector (NAV) shows how much time must pass before these stations are allowed to check the channel for idleness • Collision During handshaking Data Communications, Kwangwoon University

  8. Point Coordination Function (PCF) • An optional access method that can be implemented in an AP • A centralized, contention-free polling access method • To give priority to PCF over DCF, another set of interframe spaces has been defined: PIFS and SIFS • PIFS (PCF IFS) is shorter than the DIFS  AP using PCF has priority • Repetition interval starts with a special control frame, called a beacon frame Data Communications, Kwangwoon University

  9. MAC Layer Frame Format Data Communications, Kwangwoon University

  10. Frame Types • Three categories of frames • Management frames for initial communication between stations and APs • Control frames for accessing the channel and acknowledging frames • Data frame for carrying data and control information Data Communications, Kwangwoon University

  11. Addressing Mechanism Data Communications, Kwangwoon University

  12. Hidden Station Problems • The CTS frame in CSMA/CA handshake can prevent collision from a hidden station. Data Communications, Kwangwoon University

  13. Exposed Station Problems Data Communications, Kwangwoon University

  14. Physical Layer • Industrial, scientific, and medical (ISM) band which defines three unlicensed bands in three ranges 902-928 MHz, 2.400-4.835 GHz, and 5.725-5.850 GHz Data Communications, Kwangwoon University

  15. Physical Layer • IEEE 802.11 FHSS • IEEE 802.11 DSSS Data Communications, Kwangwoon University

  16. Physical Layer • IEEE 802.11 Infrared • IEEE 802.11a OFDM • Common data rates are 18 Mbps (PSK) and 54 Mbps (QAM) • IEEE 802.11b DSSS • High-rate direct sequence spread spectrum (HR-DSSS) • Similar to DSSS method except for the encoding method called complementary code keying (CCK), Four data rates; 1, 2, .5, 11 Mbps • IEEE 802.11g • Forward error correction and OFDM using 2.4 GHz ISM, 22- or 54-Mbps data rate Data Communications, Kwangwoon University

  17. Bluetooth: Piconet • Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously • Bluetooth network is called piconet, or a small net Data Communications, Kwangwoon University

  18. Bluetooth: Scatternet • Piconet can be combined to form what is called a scatternet. • Bluetooth device has a built-in short range radio transmitter with 2.4 GHz bandwidth. A possibility of interference with IEEE 802.11b Data Communications, Kwangwoon University

  19. Bluetooth Layers • Radio layer • 2.4 GHz ISM band divided into 79 channels of 1 MHz each • FHSS: Bluetooth hops 1600 times per second, dwell time is 625 μsec (= 1/1600 sec) • Modulation: GFSK (FSK with Gaussian bandwidth filtering) Data Communications, Kwangwoon University

  20. Bluetooth Layers • Baseband layer • TDD-TDMA (time division duplex TDMA): half-duplex communication • Single-secondary communication Data Communications, Kwangwoon University

  21. Bluetooth Layers • Baseband layer • TDD-TDMA: multiple-secondary communication Data Communications, Kwangwoon University

  22. Bluetooth Layers • Physical links • SCO (synchronous connection-oriented) • ACL (asynchronous connectionless link) • Frame format • L2CAP (Logical Link Control and Adaptation Protocol) • Multiplexing, segmentation and reassembly, QoS, group management Data Communications, Kwangwoon University

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