1. Wireless LAN Technology
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2. Wireless LAN Technology
It is LAN technology that makes use of wireless transmission
Emerged in 1980s
Makes networking simple
It satisfy the requirements for mobility, relocation and ad hoc networking and coverage of locations difficult to wire.
Saves the cost of the installation of LAN cabling
Allows resource sharing without additional wiring
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3. Wireless LAN Technology
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4. Wireless LAN Applications
LAN Extension:
Cross-building interconnect
Nomadic Access
Ad hoc networking
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5. buildings with large open areas historical buildings
LAN Extension
In the late 1980s, were marketed as substitutes for traditional wired LANs
It was not used widely because of the existing prewiring and reliance on twisted pair cabling.
But in a number of environments, there is a role for the wireless LAN as an alternative to a wired LAN.
buildings with large open areas
historical buildings
Small offices where installation and maintenance of wired LANs is not economical.
Wireless LAN linked into a wired LAN on same premises
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6. Control Module(CM) acts as an interface to the wireless LAN
LAN Extension
Backbone wired LAN such as Ethernet that supports servers a stationary workstations and one or more bridges or routers
Control Module(CM) acts as an interface to the wireless LAN
CM contains some sort of access control logic and includes either bridge or router functionality to link the wireless LAN to the backbone.
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7. Figure: A single cell Wireless LAN
LAN Extension
Figure: A single cell Wireless LAN
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8. Figure: A Multiple cell Wireless LAN
LAN Extension
Figure: A Multiple cell Wireless LAN
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9. Cross-Building Interconnect
Connect LANs in nearby buildings(wired or wireless)
Point-to-point wireless link is used
Devices connected are typically bridges or routers
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10. LAN Extension Nomadic Access
The provider's fixed antennas communicate with an antenna on the user's device.eg: WiFi
Link between LAN hub and mobile data terminal
Also useful in extended environment such as campus or cluster of buildings
Users move around with portable computers
May wish access to servers on wired LAN
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11. LAN Extension Nomadic Access
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12. Temporary peer-to-peer network set up to meet immediate need
Ad Hoc Networking
Temporary peer-to-peer network set up to meet immediate need
Network for duration of meeting
Example:
Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting
Military applications
Disaster scenarios
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13. Wireless LAN Requirements
Same as any LAN
High capacity, short distances, full connectivity, broadcast capability
Throughput: MAC protocols efficient use of wireless medium
Number of nodes: Hundreds of nodes across multiple cells
Connection to backbone LAN: Use control modules to connect to both types of LANs
Service area: 100 to 300 m
Long power consumption: Need long battery life on mobile stations
Must not require nodes to monitor access points or frequent handshakes
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14. Wireless LAN Requirements
Transmission robustness and security: Interference prone and easily eavesdropped
Collocated network operation: Two or more wireless LANs in same area
License-free operation
Handoff/roaming: Move from one cell to another
Dynamic configuration: Addition, deletion, and relocation of end systems without disruption to users
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15. Wireless LAN Categories
According to the transmission medium used, wireless LAN are categorized into:
Infrared (IR) LANs: Individual cell of IR LAN limited to single room
IR light does not penetrate opaque walls
Spread spectrum LANs: Mostly operate in ISM (industrial, scientific, and medical) bands
No Federal Communications Commission (FCC) licensing is required
Narrowband microwave: Microwave frequencies but not use spread spectrum
Some require FCC licensing
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16. Wireless LAN Categories Infrared (IR) LANs
Infrared communication is very common  Used in variety of remote control devices
An individual cell is limited to a single room because infrared light does not penetrate walls.
Infrared networking uses electromagnetic radiation with wavelengths of 820 to 890 nanometres.
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17. Wireless LAN Categories Infrared (IR) LANs
Strengths of Infrared
Spectrum for infrared virtually unlimited
Possibility of extremely high data rates
Infrared spectrum unregulated
Shares some properties of visible light
Equipment inexpensive and simple
Uses intensity modulation  IR receivers need to detect amplitude of optical signals
Reflected by light-colored objects
Ceiling reflection for entire room coverage
Does not penetrate walls
More easily secured against eavesdropping
Less interference between different rooms
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18. Wireless LAN Categories Infrared (IR) LANs
Drawback
Indoor environments experience infrared background radiation
Sunlight and indoor lighting makes noise in an infrared receiver
Transmitters of higher power required Limited by concerns of eye
safety and excessive power consumption  Limits the range
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19. Wireless LAN Categories Infrared (IR) LANs
IR Data Transmission Techniques
Directed Beam Infrared
Omni-directional Configuration
Diffused
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20. Wireless LAN Categories Infrared (IR) LANs Directed Beam Infrared
The infrared light is focused before transmitting the signal. This method increases the transmission speed.
Transmitted signal can be pointed and aimed
Used to create point-to-point links
Range depends on emitted power and degree of focusing
Used to set up a ring LAN.
Focused IR data link can have range of kilometers
Cross-building interconnect between bridges or routers
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21. Token Ring LAN using Point-to-Point IR link
Wireless LAN Categories Infrared (IR) LANs Directed Beam Infrared
Token Ring LAN using Point-to-Point IR link
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22. Single base station within line of sight of all other stations on LAN
Wireless LAN Categories Infrared (IR) LANs Omni-directional Configuration
Single base station within line of sight of all other stations on LAN
Station typically mounted on ceiling
Base station acts as a multiport repeater
Ceiling transmitter broadcasts signal received by IR transceivers
IR transceivers transmit with directional beam aimed at ceiling base unit
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23. Wireless LAN Categories  Infrared (IR) LANs Diffused
The infrared light transmitted by the sender unit fills the area (e.g. office). Therefore the receiver unit located anywhere in that area can receive the signal.
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
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24. Wireless LAN Categories  Spread spectrum LANs
Multiple-cell arrangement
Adjacent cells make use of different center frequencies within the same band to avoid interference.
Within a cell, either peer-to-peer or hub
Peer-to-peer topology
No hub
Access controlled with MAC algorithm
CSMA
Appropriate for ad hoc LANs
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25. Wireless LAN Categories  Spread spectrum LANs
Hub topology
The hub is mounted on the ceiling and connected to a backbone wired LAN as well as the stations in the wireless LAN
The hub controls the access
The station may broadcast using omnidirectional antenna
The hub is responsible for the automatic hand off of stations.
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26. Wireless LAN Categories  Spread spectrum LANs
Methods
Two methods are used:
Direct Sequence Spread Spectrum(DSSS)
Frequency Hopping Spread Spectrum(FHSS)
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27. Wireless LAN Categories  Spread spectrum LANs
Transmission Issues
Licensing regulations differ from one country to another
USA FCC authorized two unlicensed applications within the ISM band:
Spread spectrum - up to 1 watt
Very low power systems- up to 0.5 watts
MHz (915-MHz band)-Industrial
GHz (2.4-GHz band)-Scientific
GHz (5.8-GHz band)-Medical
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28. Wireless LAN Categories  Spread spectrum LANs
Bandwidth
Higher frequency means higher potential bandwidth
Large number of devices works around 900 MHz, including cordless telephones, wireless microphones, and amateur radio
Fewer devices at 2.4 GHz;
Little competition at 5.8 GHz
Higher frequency band, more expensive equipment
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29. Wireless LAN Categories  Narrowband Microwave LANs
Use of a microwave radio frequency band for signal transmission with a relatively narrow bandwidth
Just wide enough to accommodate signal
Licensed
Unlicensed
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30. Wireless LAN Categories
Licensed Narrowband RF
Microwave frequencies usable for voice, data, and video licensed within specific geographic areas to avoid interference
Use of cell configuration
Adjacent cells use non-overlapping frequency bands
All transmissions are encrypted
Licensed narrowband LAN guarantees interference-free communication
License holder has legal right to interference-free data channel
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31. Wireless LAN Categories
Unlicensed Narrowband RF
1995, Radio LAN introduced narrowband wireless LAN using unlicensed ISM spectrum
Used for narrowband transmission at low power
0.5 watts or less
Operates at 10 Mbps
5.8-GHz band
Peer-to-peer configuration
Elects one node as dynamic master
Based on location, interference, and signal strength
Master can change automatically as conditions change
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