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Transcript of 09bit046 wlan
Wireless Local Area Network
Ancy Varghese
09bit046
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
Typical WLAN Configuration:
Why WIRELESS?1. Flexibility: Nodes can be placed anywhere
2. Planning: Can be set without prior planning
3. Design: Small independent networks, or abstraction of networks
4. Robustness: It can survive disasters like Earthquake, User pulling a plug.
5. Expandability: No additional cabling or noticeable change in the architecture
Drawbacks and Limitations:1. Quality of Service: Low QoS. Low
Bandwidth, due to IR and RF, high error rates, interference
2. Proprietary Solutions: Many Vendors offering proprietary solutions but with Homogenous environment
3. Restrictions: Regulations are not same world wide
4. Safety : Interference with high tech equipments in e.g. hospitals. Specials precautions to prevent safety hazards.
5. Security: Vulnerable to hacking.
PHYSICAL layer Technologies used:
WIRELESS TECHNOLOGIES USED
INFRARED MICROWAVE RADIO
SPREAD SPECTRUM NARROW BAND TRANSMISSION
FHSS
DSSS
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
INFRARED TRANSMISSION: Strengths1. Virtually unlimited Spectrum
2. Diffused reflection by light colored objects
3. IR Spectrum Unregulated
4. Uses Intensity Modulation (Amplitude)
5. Inexpensive and Simple Equipments
6. Bound by walls:5.a Security against Interception
5.b Easy Construction of very large IR LANS
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
Transmission Techniques:
1. Directed Beam Infrared:
- Used to create point to point links.
- The range depends on emitted power and degree of focusing.
- Focused IR data link can have range of kilometers
i.e. Cross Building interconnect between bridges and routers.
2. Omni directional
- Single base stations within the line of sight of all other stations on LAN
- Station typically mounted on Ceiling
- Base station acts as a multi port repeater
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
Spread Spectrum LAN Configuration
• Multiple-cell arrangement • Within a Cell,either peer-to-peer
or hub • Peer to Peer topology
-No hub
-Access controlled with MAC algo (e.g CSMA)
-Appropriate for ad hoc networks
• Hub Topology
-Mounted on the ceiling and connected to backbone
-May Control access
-May act as a multi port repeater
-Automatic handoff of mobile stations
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
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
Wireless LAN Applications:
WIRELESS LAN APPLICATIONS
LAN
EXTENSION
CROSS-BUILDING
INTERCONNECT
NOMADIC
ACCESS
AD HOC
NETWORKING
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
Multiple Cell WLAN Configurations
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
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
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
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