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