Wifi General

What is Wi-Fi •

Wi-Fi- an acronym for Wireless Fidelity

•

Uses 802.11 networking standards- 802.11a, 802.11b, 802.11g, 802.11n

•

Wi-Fi is a wireless technology that uses radio frequency to transmit data through air.

How WiFi Works •A computer's wireless adapter translates data into a radio signal and transmits it using an antenna. •A wireless router receives the signal and decodes it. The router sends the information to the Internet using a physical, wired Ethernet connection. •The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter. •Provides NLOS capability

Brief History 802.11 Protocol

Release

-----

Jun 1997

2.4

20

0.9

2

802.11a Oct 1999

5

20

27

54

50ft/15meters

802.11b Oct 1999 2.4( 2.400– 2.500)

20

5

11

150ft/45 meters

300 ft/90 meters

DSSS

802.11g Jun 2003

20

22

54

150ft/45 meters

300 ft/90 meters

OFDM, DSSS

144

600

150feet

375feet

OFDM DSSS

23

54

802.11n Sep 2009

802.11y Nov 2008

Freq. Bandwidt Type Max net (GHz)h throughp bit rate Unlicense (MHz ut (Mbit/s) d (Mbit/s)

2.4

2.4 20/40 /5(MIMO) 3.7

20

Range Indoor Approx

Range Outdoor Approx

Modulati Range on Coonfigur ation

DSSS 100ft/30met OFDM ers

Wireless local area network standards

OFDM

Point to Multipoint

Brief History-Contd • • •

Uses 802.11 networking standards They transmit at frequencies of 2.4 GHz or 5 GHz. They use 802.11 networking standards, which come in several flavors: – 802.11a transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits the radio signal into several subsignals before they reach a receiver. This greatly reduces interference.

– 802.11b is the slowest and least expensive standard. For a while, its cost made it popular, but now it's becoming less common as faster standards become less expensive. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complementary code keying (CCK) modulation to improve speeds.

Contd…. – 802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a. – 802.11n is the newest standard that is widely available. This standard significantly improves speed and range. For instance, although 802.11g theoretically moves 54 megabits of data per second, it only achieves real-world speeds of about 24 megabits of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140 megabits per second. The standard is currently in draft form -- the Institute of Electrical and Electronics Engineers (IEEE) plans to formally ratify 802.11n by the end of 2009.

Requirements for WiFi • A wireless device with WiFi • A wireless access point (WAP) • A wired internet connection

What is an access point •

Is a device that allows wireless communication devices to connect to a wireless network using Wi-Fi, Bluetooth or related standards. The WAP usually connects to a wired network, and can relay data between the wireless devices (such as computers or printers) and wired devices on the network.

Wi-Fi-technical Aspects cal Aspects modulation schemes •

802.11b was the first widely accepted one, followed by 802.11g and 802.11n. • 802.11i amendment provides security standards for 802.11 standards. • 802.11n uses MIMO technology

802.11b • • • • • • • • •

802.11b and 802.11g use the 2.4 GHz ISM band Since they use frequencies belonging to ISM band they will suffer interference microwave ovens, cordless telephones and Bluetooth devices. To control interference they use spread spectrum modulation Modulation Scheme: DSSS Range 2.4000–2.4835 G Center frequency-2.4-2.450G No of Channels:13 Nos Bandwidth-22MHz Space b/w 2 frequencies-5MHz

Availability of channels is regulated by country, constrained in part by how each country allocates radio spectrum to various services Note: • The industrial, scientific and medical (ISM) radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment

802.11b WiFi Channels

•

Channel

802.11b WiFi Channels • •

In the United States and Canada there are 11 channels available for use in the 802.11b 2.4GHz WiFi Frequency range. This standard is defined by the IEEE. There are only 3 non-overlapping channels available in the 802.11b standard. These are Channels 1,6, and 11. For WiFi access points that are located near each other it is recommended that they each use one of the above non-overlapping channels to minimize the effects of interference.

802.11a • • • •

• •

•

Uses OFDM for air interface Uses Forward Error correction code (FEC) Because of high carrier frequency , the overall range of coverage is reduced. 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of 802.11b 12 or 13 802.11a is not interoperable with 802.11b as they operate on separate bands, except if using equipment that has a dual band capability The near absence of other interfering systems (microwave ovens, cordless phones, baby monitors) give 802.11a significant aggregate bandwidth and reliability advantages over 802.11b/g.

802.11a • • • • •

5.47 to 5.725 Bandwidth:20MHz 52 OFDM sub carriers, 48 are for data and 4 are pilot sub carriers carrier separation of 0.3125 MHz Coding Schemes: BPSK, QPSK, 16-QAM or 64-QAM

Data Rate M (Mbps)

•

Used in point to multipoint configuration

•

Access point communicates via an omni-directional antenna with one or more nomadic or mobile clients that are located in a coverage area around the access point

•

Indoor range is 30 m at 11Mbps and 90 m (300 ft) at 1 Mbit/s

•

overall bandwidth is dynamically demand shared across all the users on a channel

•

High-gain external antennas can be used in fixed point-to-point arrangements which may give ranges up to 8 kilometers (5 miles) and also at ranges up to 80–120 km (50–75 miles)

802.11n •

Coupling MIMO architecture with wider bandwidth channels offers increased physical transfer rate over 802.11a (5 GHz) and 802.11g (2.4 GHz • Data encoding: Higher data rates is achieved through Spatial coding. • Spatial coding increases data throughput via spatial multiplexing and increase range by exploiting the spatial diversity, through techniques such as Alamouti coding.

MCS

Spatial

Modulation

Coding

Data Rate

Index

Streams

Type

Rate

20 MHz channel 800ns GI

40 MHz channel 400ns GI

800ns GI

400ns GI

0

1BPSK

1/2

6.5

7.2

13.5

15

1

1QPSK

1/2

13

14.4

27

30

2

1QPSK

3/4

19.5

21.7

40.5

45

3

116-QAM

1/2

26

28.9

54

60

4

116-QAM

3/4

39

43.3

81

90

5

164-QAM

2/3

52

57.8

108

120

6

164-QAM

3/4

58.5

65

121.5

135

7

164-QAM

5/6

65

72.2

135

150

8

2BPSK

1/2

13

14.4

27

30

9

2QPSK

1/2

26

28.9

54

60

10

2QPSK

3/4

39

43.3

81

90

11

216-QAM

1/2

52

57.8

108

120

12

216-QAM

3/4

78

86.7

162

180

13

264-QAM

2/3

104

115.6

216

240

14

264-QAM

3/4

117

130

243

270

15

264-QAM

5/6

130

144.4

270

300

...

... 31

... 464-QAM

... 5/6

... 260

... 288.9

... 540

600

Adaptive Modulation • Adaptive modulation is a term denoting the ability of a radio to change its modulation scheme on the fly to adapt to varying signal conditions

Wireless Solutions

Point to Multipoint Connectivity •In Point to Multipoint connections access point are installed high in the tower above the city or on some high building and then point the client antennas to this access point.

Point to Point Connectivity •connections between two sites to achieve high data transfer speeds. •useful to create backbone link from some distant radio access point to main Internet source

Wi-Fi Hot Spots • A hotspot is a venue that offers WiFi access • A WiFi hotspot is a wireless access point that provides Internet access to – wireless network devices in public locations such as downtown centers, cafes, airports and hotels.

• Hotspots are often found at – restaurants, – train stations, – airports, – libraries, – coffee shops, – bookstores, – fuel stations, department stores, and other public places

Wi-Fi hotspot

Simple Wireless Network for Home and Small Office

How to use Wi-Fi •

The public can use a laptop, WiFi phone, PDA’s or other suitable portable device to access the Internet

•

Many schools and universities have wireless networks in their campus.

Wi-Fi Connectivity •

Requirements to use WiFi – Most new laptops and many new desktop computers come with built-in wireless transmitters. – If the laptop doesn't, a wireless adapter that plugs into the PC card slot or USB port has to be used. Desktop computers can use USB adapters, or an adapter that plugs into the PCI slot inside the computer's case can be used. These adapters can use more than one 802.11 standard.

Wireless adapters can plug into a computer's PC card slot or USB port.

•

After installation the wireless adapter and the drivers that allow it to operate, the computer should be able to automatically discover existing networks. • This means that when you turn your computer on in a WiFi hotspot, the computer will inform you that the network exists and ask whether you want to connect to it. If you have an older computer, you may need to use a software program to detect and connect to a wireless network.

Building Wi-Fi Network •

A Wi-Fi hotspot is created by installing an access point

•

An access point acts as a base station

•

When Wi-Fi enabled devices like laptops, PDA’s detects a hotspot then the device can connect to the network

Building Wi-Fi Network…..

What can you do with it? -Applications •

Quick/easy temp network access

•

The main attractive feature of this technology that it provides wireless broad connection within a specific geographic boundary

•

Provides easy connections to internet and business networks while traveling through Wi-Fi hotspots.

Why Wi-Fi •

Setup Cost-Reduced Cabling required

•

Flexibility-Quick and easy to setup in temp or permanent space

•

Mobility/Freedom-can work from any location within a specified geographical area.

•

Low installation cost

Disadvantages •

Security-Exposed to high risks

•

Speed-Slower than cable

•

Range-Limited coverage – Travels best in open space – Reduced by walls, glass, water etc

Wi-Fi Topologies •

WiFi technology offers two operating modes Ad hoc" mode Infrastructure" mode

1. 2.

"Ad hoc" mode, a peer-to-peer mode making it possible to connect two computers equipped with wireless adapters to one another; –

E.g. If you have two or more computers equipped with wireless adapters (WiFi cards), it is possible to easily connect them in a network by setting up a so-called "ad hoc" network, that is, a computer-to-computer network, without using an access point.

"Infrastructure" mode, making it possible to connect computers to a wired network using a device called an "access point", sometimes abbreviated AP. • It requires an access point •

The association of target machines with the infrastructure network is generally simpler

•

Possible for mobile computers to access the internet

Is the data secured? • Wi-Fi is an “open” standard– the access points are open i.e. the resources (network) is shared among a number of users.

How is it Open? •

We set up our home network and leave it open

•

We go to an Internet cafe, an airport, a hotel, and use their wireless. Hence data /message is not encrypted

•

Anyone can access the network within the range and so the traffic can be seen to and from..

•

data /message is not encrypted

•

IP address is not secured-i.e. anyone can get access to your IP address and hence can be used for illegal purposes

WiFi-Security/Solution • 1. 2.

Two common options for encryption: WEP WPA

WEP stands Wired Equivalent Privacy (1997-2003)-It provided security to IEEE 802.11 wireless networks By 2003 Wi-Fi Alliance came up with another security algorithm Wi-Fi Protected Access (WPA), -it is a subset of 802.11i amendment

WiFi-Security •

Use a strong password :a sufficiently strong password avoids cracking of the password.

•

Don’t broadcast your SSID :the “name” given to your wireless network. Hiding the name of the router so that people don't see it.

•

Use good wireless encryption: WEP is not exactly “good” encryption. With a freely available tool like air crack, you can sniff wireless traffic protected by WEP and crack security on that network in a matter of minutes

•

Data Encryption-WEP,WPA

•

Restrict access by MAC address: Restricting the MAC addresses allowed to connect to the network

•

Shut down the network when it’s not being used

•

Shut down your wireless network interface, too.

•

Monitor your network for intruders

•

Cover the bases: Have some kind of good firewall running, whether on a wireless router or on a laptop which is used to connect to wireless networks away from home

•

Don’t waste your time on ineffective security measures.

Points • •

Sectored antennas also called as high gain antennas transmit further and listen better. Limitations in Omnidirectional antennas: – No of users get reduced – Cell size,channel reuse,hidden nodes, multipath

How do hubs, switches, routers, and access points differ?