intro wifi

7/31/2019 Intro WiFi

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AN INTRODUCTION TO W I RELESS-F I DELITY (WI-FI)

1.0 Scope:

Wi-Fi is a registered trademark by the Wi-Fi Alliance. The products tested and

approved as "Wi-Fi Certified" are interoperable with each other, even if they are from

different manufacturer. It is Short form for Wireless-Fidelity and is meant togenerically refer to any type of 802.11 network, whether 802.11b, 802.11a, dual-

band, etc.

2.0 General description of Wi-Fi Network:

A Wi-Fi network provides the features and benefits of traditional LAN technologies

such as Ethernet and Token Ring without the limitations of wires or cables. It provides

the final few metres of connectivity between a wired network and the mobile user

thereby providing mobility, scalability of networks and the speed of installation.

WIFI is a wireless LAN Technology to deliver wireless broad band speeds up to 54

Mbps to Laptops, PCs, PDAs , dual mode wifi enabled phones etc.

In a typical Wi-Fi configuration, a transmitter/receiver (transceiver) device, called the

Access Point (AP), connects to the wired network from a fixed location using standard

cabling. A wireless Access Point combines router and bridging functions, it bridges

network traffic, usually from Ethernet to the airwaves, where it routes to computers

with wireless adapters. The AP can reside at any node of the wired network and acts as

a gateway for wireless data to be routed onto the wired network as shown in Figure-1.

It supports only 10 to 30 mobile devices per Access Point (AP) depending on the

network traffic. Like a cellular system, the Wi-Fi is capable of roaming from the AP

and re-connecting to the network through another AP. The Access Point (or the antenna

attached to the Access Point) is usually mounted high but may be mounted essentially

anywhere that is practical as long as the desired radio coverage is obtained.

Figure -1: A typical Wi-Fi Network.

Like a cellular phone system, the wireless LAN is capable of roaming from the AP and

re-connecting to the network through other APs residing at other points on the wired

network. This can allow the wired LAN to be extended to cover a much larger area than

the existing coverage by the use of multiple APs such as in a campus environment asshown in Figure 2.

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WIFi-WiMAX : Introduction to WiFi

Figure -2: Extending Wi-Fi coverage with multiple APs.

An important feature of the wireless LAN is that it can be used independent of a wired

network. It may be used as a stand alone network anywhere to link multiple computers

together without having to build or extend a wired network. Then a peer to peer

workgroup can be established for transfer or access of data. A member of the

workgroup may be established as the server or the network can act in a peer to peer

mode as Shown in Figure-3.

Figure-3: Wireless LAN workgroup.

End users access the Wi-Fi network through Wi-Fi adapters, which are implemented as

cards in desktop computers, or integrated within hand-held computers. Wi-Fi wireless

LAN adapters provide an interface between the client Network Operating System

(NOS) and the airwaves via an antenna. The nature of the wireless connection is

transparent to the NOS. Wi-Fi deals with fixed, portable and mobile stations and of

course, the physical layers used here are fundamentally different from wired media

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3.0 Wi-Fi Network Configuration:

3.1 A Wireless Peer-To-Peer Network: This mode is also known as ADHOC mode. Wi-

Fi networks can be simple or complex. At its most basic, two PCs equipped with

wireless adapter cards can set up an independent networkwhenever they are within

range of one another. This is called a peer-to-peer network. It requires no administration

or pre-configuration. In this case, each client would only have access to the resources of

the other client and not to a central server as shown in Figure-4.

Figure-4: A Wi-Fi Peer-To-Peer Network.

3.2 Client and Access Point:This is known as INFRASTUCTURE mode and is normally employed. However,

wireless gateway can be configured to enable peer to peer communication in this mode

as well.

In this mode, one Access Point is connected to the wired network and each client

would have access to server resources as well as to other clients. The specific number

client depends on the number and nature of the transmissions involved. Many real-

world applications exist where a single Access Point services from 15 to 50 client

devices as shown in Figure-5.

Figure-5: A Server and Clint Wi-Fi Network.

3.3 Multiple Access Points and Roaming:

Access points can be connected to each other through UTP cable or they can be

connected to each other over radio through wireless bridging. There is an option to

connect access points in a mesh architecture where in event of a fault in an access point

the network heals itself and connectivity is ensured through other access point. This

changeover takes place dynamically.

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Access Points have a finite range, of the order of 500 feet indoor and 1000 feet

outdoors. In a very large facility such as a warehouse, or on a college campus, it will

probably be necessary to install more than one Access Point. Access Point positioning

is done by a site survey. The goal is to blanket the coverage area with overlapping

coverage cells so that clients might range throughout the area without ever losing

network contact. The ability of clients to move seamlessly among a cluster of Access

Points is called roaming. Access Points hand the client off from one to another in a way

that is invisible to the client, ensuring unbroken connectivity as shown in Fig-6.

Figure-6: Multiple Access Points and Roaming.

3.4 Use of an Extension Point: To solve particular problems of topology, the network

designer some times uses Extension Points (EPs) to augment the network of Access

Points (APs). Extension Points look and function like Access Points, but they are not

tethered to the wired network as are APs. EPs function just as their name implies: they

extend the range of the network by relaying signals from a client to an AP or another

EP. EPs may be strung together in order to pass along messaging from an AP to far-

flung clients as shown in Figure-7.

Figure -7: Wi-Fi network with Extension Point (EP).

3.5 The Use of Directional Antennae: One last item of wireless LAN equipment to

consider is the directional antenna. Lets suppose you had a Wi-Fi network in your

building-A and wanted to extend it to a leased building-B, one mile away. One solution

might be to install a directional antenna on each building, each antenna targeting the

other.

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The antenna on A is connected to your wired network via an Access Point. The antenna

on B is similarly connected to an Access Point in that building, which enables Wi-Fi

network connectivity in that facility as shown in Figure-8.

Figure-8: A Wi-Fi network using Directional Antennae.

4.0 Benefits of Wi-Fi:

In a Wi-Fi users can access shared information without looking for a place to plug in,

and network managers can set up or augment networks without installing or moving

wires. Wi-Fi offers the following productivity, conveniences, and cost advantages over

traditional wired networks:

Mobility: Wi-Fi systems can provide LAN users with access to real-

time information anywhere in their organization. This mobility supports

productivity and service opportunities not possible with wired networks.

Installation Speed and Simplicity: Installing a Wi-Fi system can

be fast and easy and can eliminate the need to pull cable through walls and

ceilings.

Installation Flexibility: Wireless technology allows the network to

go where wire cannot go.

Reduced Cost-of-Ownership: While the initial investment required

for Wi-Fi hardware can be higher than the cost of wired LAN hardware, overall

installation expenses and life-cycle costs can be significantly lower. Long-term

cost benefits are greatest in dynamic environments requiring frequent moves,

adds, and changes.

Scalability: Wi-Fi systems can be configured in a variety of

topologies to meet the needs of specific applications and installations.Configurations are easily changed and range from peer-to-peer networks

suitable for a small number of users to full infrastructure networks of thousands

of users that allows roaming over a broad area.

It offers much high speed upto 54 Mbps which is very much greater

than other wireless access technologies like CORDECT, GSM and CDMA.

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5.0 Limitation of Wi-Fi networks:

The key areas of limitation of Wi-Fi are:

Coverage: A single Access Point can cover, at best, a radius of only about 60 metres.

Hundreds of Access Points are necessary to provide seamless coverage in small area.

For 10 square kms area roughly 650 Access Points are required, where as CDMA 20001xEV-DO requires just 09 sites.

Roaming: It lacks roaming between different networks hence wide spread coverage by

one service provider is not possible, which is the key to success of wireless technology.

Backhaul: Backhaul directly affects data rate service provider used Cable or DSL for

backhaul. Wi-Fi real world data rates are at least half of the their theoretical peak rates

due to factors such as signal strength, interference and radio overhead .Backhaul

reduces the remaining throughput further.

Interference: Wi-Fi uses unlicensed spectrum, which mean no regulator recourse

against interference. The most popular type of Wi-Fi, 802.11b uses the crowded 2.4GHz band which is already used in Bluetooth, cordless phones and microwave ovens.

Security: Wi-Fi Access Points and modems use the Wired Equivalent Privacy (WEP)

Standards, which is very susceptible to hacking and eavesdropping.

Security: WEP( Wired Equivalent Privacy) is not very secure. WPA (WIFI Protected

Access) offers much better security with the help of dynamic key encryption and

mutual authentication.

Authentication, Authorization and Accounting: In a server based configuration

whenever a laptop enters into a wifi zone, a welcome page is sent to it. User enters

username and password. It is connected through the wireless gateway(router) to AAA,

LDAP servers. Once authenticated ,user can access sites of his choice. Prepaid and

postpaid customers can be billed.

6.0 Abbreviations:

1. LAN: Local Area Network.2. AP: Access Point.

3. EP: Extension Point.

4. ISM: Industrial scientific & medical

5. MAC: Media Access Control.

6. CSMA/CA: Carrier Sense multiple Access with Collision Avoidance.7. CDMA 2000 1x EV-DO: CDMA 2000 1x Evolution Version Data Only.

8. IEEE: Institute of Electrical & Electronics Engineers.

9. OSI: Open systems Interconnect.

10. WEP: Wireless Equivalent Privacy.

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