1. Chapter 15 Wireless LANs 15.# 1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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2. Chapter6: Outline 15.1 INTRODUCTION 15.2 IEEE 802.11 PROJECT
BLUETOOTH
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3. Wireless communication is one of the fastest-growing technologies.
INTRODUCTION
Wireless communication is one of the fastest-growing technologies.
The demand for connecting devices without the use of cables is increasing everywhere.
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4. Figure 15.1: Isolated LANs: wired versus wireless
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5. Figure 15.2: Connection of a wired LAN and a wireless LAN to other
networks
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6. Access Control
An important issue concerning a wireless LAN is access control—
Answering the question of how the wireless host can get access to the shared medium.
The shared medium is free space for a wireless LAN.
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7. Access Control
The CSMA/CD algorithm does not work in wireless LANs for many reasons including these:
Wireless signal amplitude degrades proportional to the inverse square of the distance. This makes relative amplitudes somewhat meaningless with wireless communication.
The hidden station problem prevents collision detection.
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8. Figure 15.3: Hidden station problem
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9. IEEE PROJECT
IEEE has defined the specifications for a wireless LAN, called IEEE , which
covers the physical and data-link layers. It is sometimes called wireless Ethernet.
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10. 15.2.1 Architecture The standard defines two kinds of services:
BSS, the basic service set, and
ESS, the extended service set (ESS).
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11. Figure 15.4: Basic service sets (BSSs)
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12. Figure 15.6: Extended service set (ESS)
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13. MAC Sublayer
Like wired Ethernet, IEEE defines two sublayers within the data-link layer:
LLC (logical link control) handles framing, error control, flow control.
MAC (media access control) physical addressing
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14. MAC Sublayer
IEEE defines two sublayers withing the MAC sublayer:
DCF the distributed coordination function, and
PCF and point coordination function.
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15. 15.2.2 MAC Sublayer DCF the distributed coordination function, and
Uses CSMA/CA as the access method
Implements a persistence strategy with exp-backoff
Implements a DIFS after the media is idle.
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16. 15.2.2 MAC Sublayer DCF the distributed coordination function, and
PCF and point coordination function.
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17. Figure 15.6: MAC layers in IEEE 802.11 standard
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18. DIFS & SIFS
DIFS <= 50 microseconds
SIFS <= 10 microseconds
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19. Figure 15.7: Distributed Coordination Funcion: DCF
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20. PCF
Point Coordination Function, optional layer to allow for transmissions needing higher priority (quality of service)
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21. Figure 15.8: Example of repetition interval
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22. Figure 15.9: The frame format has 9 fields
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23. Frame Format FC = Frame control D = duration
SC = sequence control used for “fragmentation”
Frame body up to 2312 bytes.
FCS = CRC error detection
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24. Table 15.1: Subfields in FC field
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25. Figure 15.10: Control frames
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26. Table 15.2: Values of subfields in control frames
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27. Addressing Mechanism
The IEEE addressing mechanism specifies four cases, defined by the value of the two flags in the FC field.
Each flag can be either 0 or 1, resulting in four different situations.
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28. Table 15.3: Addresses
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29. Figure 15.11: Addressing mechanisms
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30. Figure 15.12: Exposed station problem
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31. Physical Layer
The unlicensed frequency bands in these three ranges
902–928 MHz,
2.400–4.835 GHz, and
5.725–5.850 GHz.
Are known as the ISM bands, Industrial, Scientific and Medical.
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32. Table 15.4: Specifications (DSSS = Direct Sequence...)
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33. OFDM Orthogonal Frequency Division Multiplexing
OFDM uses QAM for modulation.
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34. BLUETOOTH
Bluetooth is yet another wireless LAN technology requiring short distances between stations.
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35. A Bluetooth LAN is an ad hoc network.
The devices, (aka gadgets), find each other and make a network called a piconet.
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36. 15.3.1 Architecture Bluetooth defines two types of networks:
piconet and
scatternet.
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37. Bluetooth Piconet Up to 8* stations
One station is designated the primary
The other stations are secondary
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38. Bluetooth Piconet
The secondary stations synchronize their clocks with the primary station.
The secondary stations receive their hopping sequence from the primary station.
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39. Bluetooth Piconet
Communication is one-to-one or
One-to-many.
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40. Bluetooth Piconet
While limited to seven “active” secondary stations. It is possible to put a station in a “parked state” to allow another station on the piconet.
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41. Figure 6.17: Piconet
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42. Figure 15.18: Scatternet
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43. Bluetooth V1 1 Mbps bandwidth 2.4-2.483GHz (overlaps with 802.11b & g)
FHSS – 1600 hops per second
79 frequency channels of 1MHz each
FSK modulation
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44. Bluetooth V2
3 Mbps bandwidth
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45. Bluetooth V3 24 Mbps bandwidth
Bluetooth establishes the link and uses to achieve the 24Mbps data rate.
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46. Bluetooth Range Power Class 1 20db ~100 m Power Class 2 4 db ~10 m
Power Class 3 ~1 m
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47. Bluetooth Layers
Bluetooth uses several layers that do not exactly match those of the Internet model defined in the text book. Figure shows these layers.
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48. Figure 15.19: Bluetooth layers
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49. Bluetooth Access Method
Polling-select
The primary poles the secondary stations on even clock cycles.
If a secondary is polled, it transmits on the next odd clock cycle.
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50. Figure 6. 21: Single-secondary communication (diagram error
Figure 6.21: Single-secondary communication (diagram error!) microseconds, not milliseconds
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51. Figure 6.22: Multiple-secondary communication
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52. Figure 6.23: Frame format types
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53. Bluetooth V1 Throughput
1-slot frames, 192-Kbps
3-slot frames, 596-Kbps
5-slot frames, Kbps
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