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CPET 260 – Network I

CPET 260 – Network I. Wireless Networks Bluetooth. Wireless Networking:. IEEE 802.11 (Wi-Fi) and Home RF Advantages Fast installation Adaptable to changing environment Reduced costs in many situations Applications Hospitals Older buildings Temporary setups Warehouse & Factor Floors.

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CPET 260 – Network I

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  1. CPET 260 – Network I Wireless Networks Bluetooth

  2. Wireless Networking: • IEEE 802.11 (Wi-Fi) and Home RF • Advantages • Fast installation • Adaptable to changing environment • Reduced costs in many situations • Applications • Hospitals • Older buildings • Temporary setups • Warehouse & Factor Floors

  3. Ad-Hoc Networks & Access Points (Aps) • Ad-Hoc networks are established ‘on the fly’ • A number of computers, each with wireless NIC adapters • Communications is established by the computers interchange • Peer to Peer network • AKA – Basic Service Set (BSS) or Independent Basic Service Set (IBSS)

  4. Access Point • An AP acts as an intermediary in the network – potentially extending the distance between far points of the net. • AP can be added to a wired net to provide extend or provide additional services.

  5. Examples • D-Link DWL-1000AP • 11Mbps, 5.5Mbps, 1Mbps or auto • Supports DHCP • 100 to 300 meters

  6. Examples • D-Link DL-713 Wireless Gateway • Wireless + 3 switch ports • Supports Network Address Translation (NAT) – security • IEEE 802.11b & ‘Wi-Fi’ compatible

  7. IEEE 802.11 Standards • Spread Spectrum radio • Frequency Hopping Spread Spectrum (FHSS) • Original 802.11 std used FHSS 1Mbps • Direct Sequence Spread Spectrum (DSSS) • Supported both 1Mbps & 2Mbps • IR is included – at 1Mbps & 2Mbps • Not implemented to any great amount

  8. IEEE 802.11 Standards • The MAC layer – • Ethernet used CSMA/CD – Carrier Sense Multi-Access/Collision Detect • Required that transmission be monitored while sent • RF cannot perform monitoring while sending • CSMA/CA – Carrier Sense Multi-Access / Collision Avoidance

  9. CSMA/CA • As with CSMA/CD – the NIC listens for a carrier already in use • If detected – backs off & waits • If no detection, sends packet • Waits for ACK packet – to acknowledge receipt of data packet. • If no ACK – the lost packet is retransmitted. • Also known as Distributed Coordination Function (DCF)

  10. CSMA/CA • In a wireless network, since each node needs only to communicate to the AP – not to each other, they may be out of range of one another. • Hidden Node problem • Solved by sending RTS (request to send) + amt of time needed to the AP • AP responds with CTS

  11. CSMA/CA • All units on net receive CTS + time required • Other units back off the time granted by AP • Known as Point Coordination Function – PCF • DCF is required by IEEE 802.11, PCF is not

  12. Association / Reassociation • Provides for migration from one BSS to another, as the node moves physically • MAC layer provides

  13. Radio Wave Transmissions • FHSS versus DSSS • On 2.400 – 2.483 GHz range • Known as the ISM band (Industry, Scientific, Medical) • Spread Spectrum • Developed in WWII for security • As apposed to narrowband

  14. Spread Spectrum • Radio transmission is transmitted on a greater bandwidth than the actual transmitted data. • Resulting bandwidth is determined by a method other than by data transmitted. • Up to 1000 times wider BW

  15. FHSS versus DSSS • FHSS – uses a narrowband transmission in the range of the SS transmission • Both ends must know the starting frequency and the pattern used • No data burst longer than 400 ms for one frequency. • May skip from one to next • May skip on preset pattern

  16. FHSS versus DSSS • DSSS uses pseudo-noise signal on all frequencies not used by data burst. • Both ends know the algorithm for generating the pseudo-noise pattern • Noise is removed at receiver, leaving data

  17. What is Wi-Fi • Wireless Ethernet Compatibility Alliance (WECA) produces products using IEEE 802.11b standard • Wi-Fi extends to 11 Mbps • Designed for both home/business wireless solutions

  18. Security • 802.11 standard is Wired Equivalent Privacy (WEP) • Shared 40 bit key for security • RC4 encryption algorithm • Can be ‘broken’ easily • Work is underway for WEP2 (IEEE 802.11e)

  19. HomeRF • A home version of wireless on 2.4G ISM band • Uses FHSS technology • SWAP 2.0 Shared Wireless Access Protocol 1.6Mbps

  20. References • IEEE 802.11 DSSS Overview http://www.wi-fi.com/downloads/weca80211boverview.pdf • IEEE 802.11 Technical Tutorial http://www.wi-fi.com/downloads/IEEE_80211_Primer.pdf • Reliability of IEEE 802.11 Hi Rate DSSS WLANs in a High Density Bluetooth Environment • http://www.wi-fi.com/downloads/Coexistence_Paper_Intersil_Aug18.pdf

  21. Bluetooth Voice and Data Performance in 802.11 DSSS WLAN Environment • http://www.wi-fi.com/downloads/BT_inf802_June_8.pdf • Wi-Fi WEP Security Update http://www.wi-fi.com/pdf/Wi-FiWEPSecurity.pdf • Does Frequency Hopping Enhance Security? http://www.wi-fi.com/pdf/20010419_frequencyHopping.pdf

  22. Wi-Fi Security Update http://www.wi-fi.com/pdf/20011015_WEP_Security.pdf • 802.15 Operating Rules, PDFhttp://grouper.ieee.org/groups/802/15/pub/Rules/WPAN-Rules.pdf

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