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
4. 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
5. 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.
6. PHYSICAL layer Technologies
used:
WIRELESS TECHNOLOGIES USED
INFRARED MICROWAVE RADIO
SPREAD SPECTRUM NARROW BAND TRANSMISSION
FHSS
DSSS
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. INFRARED TRANSMISSION: Strengths
1. 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
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. 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. 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. 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. 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. Wireless LAN Requirements:
1. Throughput
2. Number of nodes
3. Connection to backbone LAN
4. Service area
5. Battery Power Consumption
6. Transmission Robustness and security
7. Collocated network operation
8. License-free operation
9. Handoff/Roaming
10. Dynamic Configuration
15. Wireless LAN Applications:
WIRELESS LAN APPLICATIONS
LAN CROSS-BUILDING NOMADIC AD HOC
EXTENSION INTERCONNECT ACCESS NETWORKING
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
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. 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. 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. 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
