09bit046 wlan

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09bit046 wlan

  1. 1. Wireless Local Area Network Ancy Varghese 09bit046
  2. 2. What basically is WLAN?• WLAN is a LAN which uses a transmission medium just like wired LANs, but instead of using guided media like fiber optics or UTP or STP, WLANs use Unguided media-the WIRELESS media.• WLAN provides all the features and benefits of traditional LAN technologies like the Ethernet and the Token Ring, but without the tethers and the limitations of the wires or cables
  3. 3. Typical WLAN Configuration:
  4. 4. Why WIRELESS?1. Flexibility: Nodes can be placed anywhere2. Planning: Can be set without prior planning3. Design: Small independent networks, or abstraction of networks4. Robustness: It can survive disasters like Earthquake, User pulling a plug.5. Expandability: No additional cabling or noticeable change in the architecture
  5. 5. Drawbacks and Limitations:1. Quality of Service: Low QoS. Low Bandwidth, due to IR and RF, high error rates, interference2. Proprietary Solutions: Many Vendors offering proprietary solutions but with Homogenous environment3. Restrictions: Regulations are not same world wide4. Safety : Interference with high tech equipments in e.g. hospitals. Specials precautions to prevent safety hazards.5. Security: Vulnerable to hacking.
  6. 6. PHYSICAL layer Technologiesused: WIRELESS TECHNOLOGIES USED INFRARED MICROWAVE RADIO SPREAD SPECTRUM NARROW BAND TRANSMISSION FHSS DSSS
  7. 7. Infrared (IR) Technology • IR systems use very high frequencies, just below visible light in the electromagnetic spectrum to carry data • Little used in commercial wireless LANs IR Data Transmission Techniques Directed Beam IR Omni directional Diffused
  8. 8. INFRARED TRANSMISSION: Strengths1. Virtually unlimited Spectrum2. Diffused reflection by light colored objects3. IR Spectrum Unregulated4. Uses Intensity Modulation (Amplitude)5. Inexpensive and Simple Equipments6. Bound by walls: 5.a Security against Interception 5.b Easy Construction of very large IR LANS
  9. 9. Drawbacks of IR:• Intense IR background radiation may induce Noise: - Sunlight and Indoor lighting -Ambient radiation appears as a noise in IR receivers• Solution of the above problem induces concerns of eye safety and Excessive power consumption
  10. 10. Transmission Techniques: 1. Directed Beam 2. Omni directional Infrared:- Used to create point to point - Single base stations within links. the line of sight of all other- The range depends on emitted stations on LAN power and degree of focusing. - Station typically mounted on- Focused IR data link can have Ceiling range of kilometers - Base station acts as a multi i.e. Cross Building interconnect port repeater between bridges and routers.
  11. 11. 3.Diffused- All IR transmitters focused and aimed at a point on diffusely reflecting ceiling- IR radiation strikes ceiling- Reradiated Omni directionally- Picked up by all receivers
  12. 12. Spread Spectrum LAN Configuration • Hub Topology• Multiple-cell arrangement -Mounted on the ceiling and• Within a Cell,either peer-to-peer connected to backbone or hub -May Control access• Peer to Peer topology -May act as a multi port -No hub repeater -Access controlled with MAC -Automatic handoff of mobile algo (e.g CSMA) stations -Appropriate for ad hoc networks
  13. 13. Narrowband Radio• User information is transmitted & received on a specific radio frequency• Radio signal frequency is kept as narrow as possible• This allows the ability to just pass the information• Undesirable crosstalk between communication channels is avoided by carefully coordinating different users on different channel frequencies• Licensed & unlicensed
  14. 14. Wireless LAN Requirements:1. Throughput2. Number of nodes3. Connection to backbone LAN4. Service area5. Battery Power Consumption6. Transmission Robustness and security7. Collocated network operation8. License-free operation9. Handoff/Roaming10. Dynamic Configuration
  15. 15. Wireless LAN Applications: WIRELESS LAN APPLICATIONS LAN CROSS-BUILDING NOMADIC AD HOC EXTENSION INTERCONNECT ACCESS NETWORKING
  16. 16. LAN Extension:• Wireless LAN linked into a wired LAN on same premises – Wired LAN • Backbone • Support Servers and Stationary workstations - Wireless LAN - Stations in large open areas - Manufacturing plants, stock exchange trading floors, and warehousing
  17. 17. Multiple Cell WLAN Configurations
  18. 18. Cross Building Interconnect • Connect LANS in nearby buildings – Wired or Wireless LANS • Point to Point wireless link is used • Devices connected are typically bridges or routers
  19. 19. Nomadic Access• Wireless link between LAN hub and mobile data terminal equipped with antenna – Laptop computer or Notepad computer• Uses – Transfer data from portable computer to office server – Extended environment such as Campus
  20. 20. Ad hoc Networking• Temporary peer to peer network set up to meet immediate need• Eg: – Group of employees with laptop convene for a meeting; employees link computers in a temporary network for duration of meeting
  21. 21. References:• IEEE 802.11 Fundametals CISCO Publications• Wireless Communications and Networking, 4/e William Stallings• Mobile Communications, 2/e Jochen Schiller• 802.11 Wireless Networks, Mathew Gast

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