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Network Communications Chapter 15

Network Communications Chapter 15. Wireless LANs. IEEE 802.11b. 11 Mbit/s Encrypted (but questionable security). Figure 15.1: Peer-to-Peer. Figure 15.2: Access Point. Multiple Access Points. Supports roaming. Figure 15.3. Other Wireless Systems. InfraRed: Short range, slow connection

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Network Communications Chapter 15

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  1. Network CommunicationsChapter 15 Wireless LANs

  2. IEEE 802.11b • 11 Mbit/s • Encrypted (but questionable security) Figure 15.1: Peer-to-Peer Figure 15.2: Access Point

  3. Multiple Access Points • Supports roaming Figure 15.3

  4. Other Wireless Systems • InfraRed: Short range, slow connection • Bluetooth: Short range, fast connection • Cell/PCS: Wide Area Network • CDPD: 10 Kbit/sec data on old analog cell systems (Cellular Digital Packet Data) • GSM: 13 Kbit/sec data (European cell standard) • G3: High Speed (promised)

  5. Radio Frequency Technology • Wavelength • C = 3*108 m/sec • F = frequency (Hz) • Modulation • Narrow Band (AM, FM) • Wide Band (Spread Spectrum) Figure 15.4 Figure 15.5: Narrow Band Figure 15.6: Spread Spectrum

  6. Industrial, Scientific, and Medical Frequency Bands Figure 15.7

  7. Spread Spectrum • Frequency Hopping: Invented by Heddy Lamar during WWII • Direct Sequence : Invented at ITT Labs in Nutley NJ ~1950 Figure 15.8: frequency Hopping Spread Spectrum

  8. Spread Spectrum (cont.) • Spread Spectrum Properties • Difficult to jam • Difficult toeavesdrop • Less interferencewith other services Figure 15.9: Direct Sequence Spread Spectrum

  9. Antenna Information Exclusive Modulator Amplifier OR Pseudo random code Carrier frequency Direct Sequence Hardware Figure 15.10

  10. CSMA/CA Carrier Sense Multiple Access / Collision Avoidance Figure 15.11 Figure 15.12

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