WiFi WiFi is the wireless way to handle networking. Wi-fi is a wireless technology that uses radio...

WiFiWiFi

WiFiWiFi is the wireless way to handle networking. is the wireless way to handle networking. Wi-fi is a wireless technology that usesWi-fi is a wireless technology that uses radio frequency to transmit data throughradio frequency to transmit data through the airthe air It is also known as It is also known as 802.11 networking802.11 networking. . The big advantage of WiFi is its simplicity.The big advantage of WiFi is its simplicity.

Walkie-Talkie NetworkWalkie-Talkie Network

If you want to understand wireless If you want to understand wireless networking at its simplest level, think networking at its simplest level, think about a pair of walkie-talkie.about a pair of walkie-talkie.

These are small radios that can transmit These are small radios that can transmit and receive radio signals. and receive radio signals.

The only problem would be that the data The only problem would be that the data rate would be very slow. rate would be very slow.

Another problem: the walkie-talkies could Another problem: the walkie-talkies could not be used to connect to the internet.not be used to connect to the internet.

WiFi’s Radio TechnologyWiFi’s Radio Technology The radios used in WiFi are not so different from The radios used in WiFi are not so different from

the radios used in walkie-talkies. the radios used in walkie-talkies.

They have the ability to transmit and receive. They have the ability to transmit and receive.

They have the ability to convert 1s and 0s into They have the ability to convert 1s and 0s into radio waves and then back into 1s and 0s. radio waves and then back into 1s and 0s.

There are major differences, of course.There are major differences, of course.

WiFi’s Radio Technology WiFi’s Radio Technology (Cont’d)(Cont’d)

WiFi radios that work with the 802.11b and WiFi radios that work with the 802.11b and 802.11g standards transmit at 2.4 GHz, 802.11g standards transmit at 2.4 GHz, while those that comply with the 802.11a while those that comply with the 802.11a standard transmit at 5 GHz. The higher standard transmit at 5 GHz. The higher frequency allows higher data rates. frequency allows higher data rates.

The radios used for WiFi have the ability to The radios used for WiFi have the ability to change frequencies,i.e change frequencies,i.e frequency hop frequency hop between channels.between channels.

Wireless Networking StandardsWireless Networking Standards WiFi refers to the protocols that allow WiFi refers to the protocols that allow

wireless networking.wireless networking.

These protocols are codified in standards.These protocols are codified in standards.

Standards are mutually agreed upon rules Standards are mutually agreed upon rules adopted by the industry on how the adopted by the industry on how the wireless networks operate.wireless networks operate.

There are several standards that enable There are several standards that enable wireless local area networks (WLANs).wireless local area networks (WLANs).

802.11b, 802.11a, and 802.11g802.11b, 802.11a, and 802.11g

802.11b was first to reach the 802.11b was first to reach the marketplace.802.11b transmits at 2.4 GHz marketplace.802.11b transmits at 2.4 GHz and go up to 11 Mbps. and go up to 11 Mbps.

802.11a was next. It operates at 5 GHz 802.11a was next. It operates at 5 GHz and can handle up to 54 Mbps. and can handle up to 54 Mbps.

802.11g is a mix of both worlds. It 802.11g is a mix of both worlds. It operates at 2.4Ghz but it has the 54 operates at 2.4Ghz but it has the 54 megabits per second speed of 802.11a. megabits per second speed of 802.11a.

802.11b802.11b

Any 802.11b signal occupies Any 802.11b signal occupies approximately 30 MHz. approximately 30 MHz.

Thus, 802.11b signal overlaps with Thus, 802.11b signal overlaps with several adjacent channel several adjacent channel frequencies. frequencies.

Any given area can therefore support Any given area can therefore support at most 3 access points (operating at most 3 access points (operating on different channels) at once. on different channels) at once.

802.11b (Cont’d)802.11b (Cont’d)

2

1

3

AccessPoint

Neighboring AP’s use different channels to reduce interference. “Reuse cluster” size is equal to 3.

802.11b (Cont’d)802.11b (Cont’d)

11 Mbps

5.5 Mbps

2 Mbps

802.11a802.11a

802.11a specification operates at radio frequencies between 5.15 and 802.11a specification operates at radio frequencies between 5.15 and 5.825 GHz, i.e. 802.11a utilizes 300 MHz bandwidth in Unlicensed National 5.825 GHz, i.e. 802.11a utilizes 300 MHz bandwidth in Unlicensed National Information Infrastructure (U-NII) band.Information Infrastructure (U-NII) band.

The FCC has divided total 300 MHz in this band into three distinct 100 MHz The FCC has divided total 300 MHz in this band into three distinct 100 MHz bands: low, middle, and high, each with different legal maximum power.bands: low, middle, and high, each with different legal maximum power.

Band ChannelHigh band 5.725-5.825 GHz 9-12Middle band 5.25-5.35 GHz 5-8

Low band 5.15-5.25 GHz 1-4

802.11a (Cont’d)802.11a (Cont’d)

The low and middle bands have a The low and middle bands have a total of 200 MHz of frequency.total of 200 MHz of frequency.

This 200 MHz supports 8 non-This 200 MHz supports 8 non-overlapping channels.overlapping channels.

802.11a (Cont’d)802.11a (Cont’d)

1

2

3

AccessPoint

4

5

6

7

8

Neighboring AP’s use different channels to reduce interference. “Reuse cluster” size is equal to 8.

802.11a (Cont’d)802.11a (Cont’d)

54 Mbps

48 Mbps36 Mbps

24 Mbps

12 Mbps2 Mbps

5.5 Mbps

11 Mbps

802.11a 802.11b

802.11g802.11g

802.11g operates over 3 non-overlapping 802.11g operates over 3 non-overlapping channels.channels.

802.11g operates in 2.4 GHz band but it 802.11g operates in 2.4 GHz band but it delivers data rates from 6 Mbps to 54 delivers data rates from 6 Mbps to 54 Mbps. Mbps.

802.11g802.11g

Once again, 802.11g’s "backward Once again, 802.11g’s "backward compatibility" with 802.11b.compatibility" with 802.11b.

So both 11a and 11g offer the same data So both 11a and 11g offer the same data rates. Which is better?rates. Which is better?

Comparing 11a and 11g Comparing 11a and 11g (Cont’d)(Cont’d)

802.11a operates in underused 5 GHz band; 802.11a operates in underused 5 GHz band; 802.11g operates in heavily used 2.4 GHz band.802.11g operates in heavily used 2.4 GHz band.

Higher number of channels in 11a allows more Higher number of channels in 11a allows more flexibility in avoiding interference.flexibility in avoiding interference.

802.11a has range 150-300 ft in practical 802.11a has range 150-300 ft in practical scenarios. 11g has range comparable to 11b scenarios. 11g has range comparable to 11b (approximately 1000 ft).(approximately 1000 ft).

11a range is smaller than 11b and 11g. This is 11a range is smaller than 11b and 11g. This is because 11a operates at a much higher because 11a operates at a much higher frequency band.frequency band.

Comparing 11a and 11g Comparing 11a and 11g (Cont’d)(Cont’d)

Because of its smaller range, 11a requires Because of its smaller range, 11a requires more Access Points to a region, thereby more Access Points to a region, thereby increasing cost. It is the most expensive of increasing cost. It is the most expensive of the three options.the three options.

802.11b is the cheapest and most popular 802.11b is the cheapest and most popular WLAN option.WLAN option.

802.11g is more expensive than 11b but 802.11g is more expensive than 11b but cheaper than 11a. cheaper than 11a.

What does a typical 802.11 What does a typical 802.11 Packet look like?Packet look like?

Typical 802.11 packet:Typical 802.11 packet:

PreamblePreamble PLCP (Physical Layer Convergence PLCP (Physical Layer Convergence

Procedure)Procedure) DataData CRC is the cyclic redundancy checkCRC is the cyclic redundancy check

Preamble PLCP Header Data CRC

How are Multiple Transmitters How are Multiple Transmitters Supported?Supported?

In 802.11 systems, only one user is In 802.11 systems, only one user is allowed to communicate with a receiver at allowed to communicate with a receiver at a time (cannot use another frequency a time (cannot use another frequency channel support a second or third channel support a second or third additional user). additional user).

The way the one user is selected depends The way the one user is selected depends on the carrier sense multiple access with on the carrier sense multiple access with collision avoidance (CSMA/CA) random collision avoidance (CSMA/CA) random access method.access method.

CSMACSMA

To help illustrate the operation of CSMA, we To help illustrate the operation of CSMA, we will use an analogy of a dinner table will use an analogy of a dinner table conversation. conversation.

Let’s represent our wireless medium as a Let’s represent our wireless medium as a dinner table, and let several people dinner table, and let several people engaged in polite conversation at the table engaged in polite conversation at the table represent the wireless nodes. represent the wireless nodes.

CSMA (Cont’d)CSMA (Cont’d)

The term The term multiple accessmultiple access covers what covers what we already discussed above: When one we already discussed above: When one wireless device transmits, all other devices wireless device transmits, all other devices using the wireless medium hear the using the wireless medium hear the transmission.transmission.

2 Way Handshake2 Way Handshake

Node with packet to send monitors channel. Node with packet to send monitors channel.

If channel idle for specified time interval called If channel idle for specified time interval called DIFS, then node transmits.DIFS, then node transmits.

If channel busy, then If channel busy, then • node continues to monitor until channel idle node continues to monitor until channel idle

for DIFS.for DIFS.• At this point, terminal backs-off for random At this point, terminal backs-off for random

time (collision avoidance) and attempts time (collision avoidance) and attempts transmitting after waiting this random amount transmitting after waiting this random amount of time.of time.

2 Way Handshake (Cont’d)2 Way Handshake (Cont’d) First way of the 2 way handshake was for the First way of the 2 way handshake was for the

transmitter to send its information packet to transmitter to send its information packet to the destination node, after following the the destination node, after following the collision avoidance method described above.collision avoidance method described above.

If the packet reaches the destination without If the packet reaches the destination without problems, the destination sends a short problems, the destination sends a short packet over the wireless medium packet over the wireless medium acknowledging the correct reception.acknowledging the correct reception.

This packet is typically called an ACK packet. This packet is typically called an ACK packet. ACK is the second way of the 2 way ACK is the second way of the 2 way handshake.handshake.

4 Way Handshake4 Way Handshake

““Listen before you talk”Listen before you talk”

If medium is busy, node backs-off for a If medium is busy, node backs-off for a random amount of time after waiting DIFS, random amount of time after waiting DIFS, just as before.just as before.

But now, instead of packet, sends a short But now, instead of packet, sends a short message: Ready to Send (RTS). This message: Ready to Send (RTS). This message is basically attempting to inform message is basically attempting to inform others that “I have something to send.”others that “I have something to send.”

4 Way Handshake (Cont’d)4 Way Handshake (Cont’d)

Access Point Laptop

RTS

CTS

Data

ACK

Adding WiFi to Your ComputerAdding WiFi to Your Computer

One of the best things about WiFi is how One of the best things about WiFi is how simple it is. simple it is.

Many new laptops already come with a Many new laptops already come with a WiFi card built in -- in many cases you WiFi card built in -- in many cases you don't have to do anything to start using don't have to do anything to start using WiFi. WiFi.

It is also easy to add a WiFi card to an It is also easy to add a WiFi card to an older laptop or a desktop PC. older laptop or a desktop PC.

Adding WiFi to an Older Adding WiFi to an Older ComputerComputer

802.11a, 802.11b or 802.11g network 802.11a, 802.11b or 802.11g network card. card. • For a laptop, this card will normally be a For a laptop, this card will normally be a

PCMCIA cardPCMCIA card• For a desktop machine, a PCI cardFor a desktop machine, a PCI card

Install the card Install the card

Adding WiFi to an Older Adding WiFi to an Older ComputerComputer

Install the drivers for the card Install the drivers for the card Find an 802.11 Find an 802.11 hotspothotspot.. Access the hotspot. Access the hotspot.

Locating HotspotsLocating Hotspots

There are many WiFi hotspots now There are many WiFi hotspots now available in public places like available in public places like restaurants, hotels, libraries and airports. restaurants, hotels, libraries and airports. For example, Starbucks. For example, Starbucks.

You can also create your own hotspot in You can also create your own hotspot in your home, as we will see in a little bit.your home, as we will see in a little bit.

One way to find a hotspot is to go on-One way to find a hotspot is to go on-line. line.

Finding Hotspots O-LineFinding Hotspots O-Line

Connecting to a HotspotConnecting to a Hotspot

There are actually two steps to making a There are actually two steps to making a connection.connection.

The first is to have your notebook "talk" to The first is to have your notebook "talk" to

the hotspotthe hotspot

On the newest machines, an 802.11 card will On the newest machines, an 802.11 card will automatically connect with an 802.11 hotspot automatically connect with an 802.11 hotspot and a network connection will be established.and a network connection will be established.

Connecting to a Hotspot Connecting to a Hotspot (Cont’d)(Cont’d)

On older machines you often have to On older machines you often have to go through a simple 3-step process go through a simple 3-step process to connect to a hotspot.to connect to a hotspot.


Access the software for the 802.11 card -- Access the software for the 802.11 card -- normally there is an icon for the card down in normally there is an icon for the card down in the system tray at the bottom right of the the system tray at the bottom right of the screen. screen.

Click the "Search button" in the software. The Click the "Search button" in the software. The card will search for all of the available hotspots card will search for all of the available hotspots in the area and show you a list. in the area and show you a list.

Double-click on one of the hotspots to connect Double-click on one of the hotspots to connect to it. to it.


On older machines you often have to go On older machines you often have to go through a simple 3-step process to through a simple 3-step process to connect to a hotspot.connect to a hotspot.

Find what is the Find what is the SSIDSSID of the hotspot of the hotspot All the search feature (in newer All the search feature (in newer

equipment) is doing is grabbing these two equipment) is doing is grabbing these two pieces of information from the radio pieces of information from the radio signals generated by the hotspot and signals generated by the hotspot and displaying them for you. displaying them for you.


On most notebook models, you will see On most notebook models, you will see some sort of signal icon on the bottom some sort of signal icon on the bottom right hand corner of your screen or a lit right hand corner of your screen or a lit indicator on the notebook itself, which will indicator on the notebook itself, which will give you feedback for "On" and signal give you feedback for "On" and signal strength (a red screen means your radio is strength (a red screen means your radio is Off; a green screen indicates it is On). Off; a green screen indicates it is On).

OFF ON


You can also see the quality of the signal You can also see the quality of the signal by clicking on the radio icon (may vary by clicking on the radio icon (may vary by system): by system):


Sign up with a wireless Internet service provider Sign up with a wireless Internet service provider and configure your notebook according to their and configure your notebook according to their instructions. instructions.

If you don't subscribe to a service, chances are If you don't subscribe to a service, chances are you will need to use your credit card to pay for you will need to use your credit card to pay for access every time you want to connect.access every time you want to connect.

After this, you will end up at the log-on page of After this, you will end up at the log-on page of the wireless provider (or, in some cases, the the wireless provider (or, in some cases, the wireless location). wireless location).


Enter your user name and password if Enter your user name and password if you are already a customer. you are already a customer.

Once you successfully log on, you should Once you successfully log on, you should see the following icon in your tool bar, see the following icon in your tool bar, indicating the connection has been indicating the connection has been made: made:

WiFi SecurityWiFi Security

WiFi hotspots can be open or secure. WiFi hotspots can be open or secure.

If a hotspot is open, then anyone with a If a hotspot is open, then anyone with a WiFi card can access the hotspot. WiFi card can access the hotspot.

If it is secure, then the user needs to know If it is secure, then the user needs to know a a WEP keyWEP key to connect. to connect.

WEP stands for Wired Equivalent PrivacyWEP stands for Wired Equivalent Privacy

WiFi Security (Cont’d)WiFi Security (Cont’d)

WEP is an encryption system for the data WEP is an encryption system for the data that 802.11 sends through the air. that 802.11 sends through the air.

Specifically, it is the process of encoding Specifically, it is the process of encoding bit stream in such a way that only the bit stream in such a way that only the person (or computer) with the person (or computer) with the keykey (a (a digital sequence) can decode it.digital sequence) can decode it.

Setting up a Hotspot at HomeSetting up a Hotspot at Home

If you already have several computers If you already have several computers hooked together on an Ethernet network hooked together on an Ethernet network and want to add a wireless hotspot to the and want to add a wireless hotspot to the mix, you can purchase a mix, you can purchase a Wireless Wireless Access PointAccess Point and plug it into the and plug it into the Ethernet network. Ethernet network.

Wireless Access Point

Setup #1Setup #1

WiFi RangeWiFi Range

In a typical home, hotspot will In a typical home, hotspot will provide coverage for about 100 feet provide coverage for about 100 feet (30.5 meters) in all directions, (30.5 meters) in all directions, although walls and floors do cut although walls and floors do cut down on the range. down on the range.

One Type of AmplifierOne Type of Amplifier

Or a directionalantenna can beused to givebetter range in a particulardirection.

Another Way to Amplify WiFi Another Way to Amplify WiFi SignalsSignals

A WiFi repeateris installed to extend coverage.

WirelessAccess Point

Configuring a HotspotConfiguring a Hotspot

Most wireless access points come with Most wireless access points come with default values built-in. default values built-in.

Once you plug them in, they start working Once you plug them in, they start working with these default values. with these default values.

However, you may want to change things. However, you may want to change things.

You normally get to set three things on You normally get to set three things on your access point.your access point.

Things to Configure in a HotspotThings to Configure in a Hotspot

The SSID -- Service Set IDentifier is a sequence of The SSID -- Service Set IDentifier is a sequence of charactersthat uniquely names a WLAN.charactersthat uniquely names a WLAN.

The channel – the radio link used by access The channel – the radio link used by access point/router to communicate to wireless devices.point/router to communicate to wireless devices.

The WEP key -- The default is to disable The WEP key -- The default is to disable WEP. WEP.

ApplicationsApplications

Common applications for Wi-Fi Common applications for Wi-Fi include include Internet and and VoIP phone phone access, access, gaming, and network , and network connectivity for connectivity for consumer electronics such as such as televisions, , DVD players, and , and digital camerasdigital cameras

Advantages of Wi-FiAdvantages of Wi-Fi

DisadvantagesDisadvantages

Planning – Depending on the goalPlanning – Depending on the goal Security – Greater exposure to risksSecurity – Greater exposure to risks AccessAccess Compromising DataCompromising Data Denial of ServiceDenial of Service Speed – Slower than cableSpeed – Slower than cable Range – Affected by various mediumRange – Affected by various medium

Difference between Bluetooth and Difference between Bluetooth and Wi-FiWi-Fi

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