WIRELESS LAN

Presented by

SUBRATA CHAKRABORTYDept- Information TechnologyRoll No-IT-48/07

1

WHAT IS WIRELESS LAN

A wireless LAN or WLAN is the linking of more devices without the use of wires.

WLAN utilizes the modulation technology based on radio waves to communicate between devices in a limited network area.

It gives users the mobility to move around within a broad coverage area & still be connected to the network.

2

WHY WIRELESS LAN

Previously Ethernet LANs was used,which was very costly, messy & movement of those LANs was difficult.To reduce this problems related to Wired LANs the concept of Wireless LAN has evolved.

This is very much cost effective,less messy & movement of this LANs are very easy because in this type of LANs, problems related to wires are removed.

3

TYPES OF WLAN

There are two types of WLAN:- IEEE 802.11 - 802.11b

- 802.11a

- 802.11g Bluetooth

4

IEEE 802.11 WLAN(ARCHITECTURE)

The standard defines two kinds of services

i) Basic Service Set(BSS) ii) Extended Service Set(ESS)

BSS:- Set of all stations that can communicate with

each other.

Access Point:- Base stations for the wireless network.

5

IEEE 802.11 WLAN(ARCHITECTURE)

ESS:- Set of connected two or more BSS. It uses two types

of stations: mobile and stationary. Distribution System:- Wired LAN through which BSSs are connected. Station:- All components that can connect into a wireless

medium in a network. Three types of stations: No-transition, BSS-transition ESS-transition

6

802.11 WIRELESS LAN

Provides network connectivity over wireless media

An Access Point(AP) is installed to act as the Bridge between Wireless and Wired network

An AP is connected to wired network and is equipped with antenna to provide wireless connectivity

7

802.11 WIRELESS LAN

Range depends on structural hindrances and RF gain of the antenna at the Access Point.

To service larger areas, multiple APs may be installed with 20-30% overlap

A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP.

8

MAC SUBLAYER

IEEE 802.11 defines two MAC sublayers:- i) Distributed Coordination Function(DCF) ii) Point Coordination Function(PCF)DCF:- One of the two protocols defined by IEEE at the MAC

sublayer is called the distributed coordination function. Wireless LANs cannot implement CSMA/CD for three reasons:-

1. For collision detection a station must be able to send data & receive collision signals at the same time. This can mean costly stations & increased bandwidth requirements.

2. Collision may not be detected because of the hidden station problem.

3. The distance between stations can be great. Signal fading could prevent a station at one end from hearing a collision at the other end.

9

MAC SUBLAYER

PCF:-

-The point coordination function is an optional access method that can be implemented in an infrastructure network.

-PCF has a centralized,contention-free access method. The AP performs polling for stations that are capable of being polled.

10

WLAN : 802.11B

Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4-GHz band.

802.11b systems will interoperate with 1 Mbps and 2 Mbps 802.11 DSSS system but not with FHSS systems.

Uses Complementary Code Keying(CCK)

11

WLAN : 802.11A

Operates in 5-GHz band. Incompatible with devices operating in 2.4-

GHz. Support data rates up to 54 Mbps.

12

WLAN : 802.11G

IEEE 802.11g defines forward error correction using the 2.4-GHz band

The modulation technique achieves a 22 Mbps or 54 Mbps data rates on the 2.4-GHz band.

13

SYSTEM ARCHITECTURE

Two basic system architectures:- a) Ad hoc b) Infrastructure based

14

AD HOC WIRELESS LANS

A BSS without an AP is called as Ad hoc network.

A group of stations using the same radio frequency..

15

INFRASTRUCTURE BASED WIRELESS LANS

A BSS with an Access Point is called an Infrastructure based network.

Distribution system connects cells via access point to form a single network..

16

BLUETOOTH

Short-range wireless LAN technology. It is an ad hoc network. It connects the device of different functions. A bluetooth device has the data rate of 1

Mbps with a 2.4-GHz bandwidth It defines two types of networks:- Piconet &

Scatternet.

17

ADVANTAGES & DISADVANTAGES OF WLAN Advantages:- i) Convenience

ii) Productivity

iii) Deployment

iv) Expandability

v) Cost

Disadvantages:- i) Security

ii) Range

iii) Reliability

iv) Speed

18

REFERENCES

Data communications & Networking(Forouzan)

WWW.Google.Com

19

THANK YOU

20