WiFi     WiFi is the wireless way to handle networking. Wi-fi is

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

Walkie-Talkie Network If you want to understand wireless networking at its simplest level, think about a pair of walkie-talkie. These are small radios that can transmit and receive radio signals. The only problem would be that the data rate would be very slow. Another problem: the walkie-talkies could not be used to connect to the internet.

WiFi’s Radio Technology The radios used in WiFi are not so different from the radios used in walkie-talkies. They have the ability to transmit and receive. They have the ability to convert 1s and 0s into radio waves and then back into 1s and 0s. There are major differences, of course.

WiFi’s Radio Technology (Cont’d) WiFi radios that work with the 802.11b and 802.11g standards transmit at 2.4 GHz, while those that comply with the 802.11a standard transmit at 5 GHz. The higher frequency allows higher data rates. The radios used for WiFi have the ability to change frequencies,i.e frequency hop between channels.

Wireless Networking Standards WiFi refers to the protocols that allow wireless networking. These protocols are codified in standards. Standards are mutually agreed upon rules adopted by the industry on how the wireless networks operate. There are several standards that enable wireless local area networks (WLANs).

802.11b, 802.11a, and 802.11g 802.11b was first to reach the marketplace.802.11b transmits at 2.4 GHz and go up to 11 Mbps. 802.11a was next. It operates at 5 GHz and can handle up to 54 Mbps. 802.11g is a mix of both worlds. It operates at 2.4Ghz but it has the 54 megabits per second speed of 802.11a.

802.11b Any 802.11b signal occupies approximately 30 MHz. Thus, 802.11b signal overlaps with several adjacent channel frequencies. Any given area can therefore support at most 3 access points (operating on different channels) at once.

802.11b (Cont’d) Neighboring AP’s use different channels to reduce interference. “Reuse cluster” size is equal to 3. Access Point 1 2 3

802.11b (Cont’d) 2 Mbps 5.5 Mbps 11 Mbps

802.11a 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 Information Infrastructure (U-NII) band. 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. Band High band 5.725-5.825 GHz Middle band 5.25-5.35 GHz Low band 5.15-5.25 GHz Channel 9-12 5-8 1-4

802.11a (Cont’d) The low and middle bands have a total of 200 MHz of frequency. This 200 MHz supports 8 nonoverlapping channels.

802.11a (Cont’d) Neighboring AP’s use different channels to reduce interference. “Reuse cluster” size is equal to 8. Access Point 1 7 2 3 6 4 5 8

802.11a (Cont’d) 802.11a 12 Mbps 24 Mbps 802.11b 2 Mbps 5.5 Mbps 36 Mbps 48 Mbps 11 Mbps 54 Mbps

802.11g 802.11g operates over 3 non-overlapping channels. 802.11g operates in 2.4 GHz band but it delivers data rates from 6 Mbps to 54 Mbps.

802.11g Once again, 802.11g’s "backward compatibility" with 802.11b. So both 11a and 11g offer the same data rates. Which is better?

Comparing 11a and 11g (Cont’d) 802.11a operates in underused 5 GHz band; 802.11g operates in heavily used 2.4 GHz band. Higher number of channels in 11a allows more flexibility in avoiding interference. 802.11a has range 150-300 ft in practical scenarios. 11g has range comparable to 11b (approximately 1000 ft). 11a range is smaller than 11b and 11g. This is because 11a operates at a much higher frequency band.

Comparing 11a and 11g (Cont’d) Because of its smaller range, 11a requires more Access Points to a region, thereby increasing cost. It is the most expensive of the three options. 802.11b is the cheapest and most popular WLAN option. 802.11g is more expensive than 11b but cheaper than 11a.

What does a typical 802.11 Packet look like? Typical 802.11 packet: Preamble PLCP Header Data Preamble PLCP (Physical Layer Convergence Procedure) Data CRC is the cyclic redundancy check CRC

How are Multiple Transmitters Supported? In 802.11 systems, only one user is allowed to communicate with a receiver at a time (cannot use another frequency channel support a second or third additional user). The way the one user is selected depends on the carrier sense multiple access with collision avoidance (CSMA/CA) random access method.

CSMA To help illustrate the operation of CSMA, we will use an analogy of a dinner table conversation. Let’s represent our wireless medium as a dinner table, and let several people engaged in polite conversation at the table represent the wireless nodes.

CSMA (Cont’d) The term multiple access covers what we already discussed above: When one wireless device transmits, all other devices using the wireless medium hear the transmission.

2 Way Handshake Node with packet to send monitors channel. If channel idle for specified time interval called DIFS, then node transmits. If channel busy, then node continues to monitor until channel idle for DIFS. At this point, terminal backs-off for random time (collision avoidance) and attempts transmitting after waiting this random amount of time.

2 Way Handshake (Cont’d) First way of the 2 way handshake was for the transmitter to send its information packet to the destination node, after following the collision avoidance method described above. If the packet reaches the destination without problems, the destination sends a short packet over the wireless medium acknowledging the correct reception. This packet is typically called an ACK packet. ACK is the second way of the 2 way handshake.

4 Way Handshake “Listen before you talk” If medium is busy, node backs-off for a random amount of time after waiting DIFS, just as before. But now, instead of packet, sends a short message: Ready to Send (RTS). This message is basically attempting to inform others that “I have something to send.”

4 Way Handshake (Cont’d) Access Point Laptop RTS CTS Data ACK

Adding WiFi to Your Computer One of the best things about WiFi is how simple it is. Many new laptops already come with a WiFi card built in -- in many cases you don't have to do anything to start using WiFi. It is also easy to add a WiFi card to an older laptop or a desktop PC.

Adding WiFi to an Older Computer 802.11a, 802.11b or 802.11g network card. For a laptop, this card will normally be a PCMCIA card For a desktop machine, a PCI card Install the card

Adding WiFi to an Older Computer Install the drivers for the card Find an 802.11 hotspot. Access the hotspot.

Locating Hotspots There are many WiFi hotspots now available in public places like restaurants, hotels, libraries and airports. For example, Starbucks. You can also create your own hotspot in your home, as we will see in a little bit. One way to find a hotspot is to go online.

Finding Hotspots O-Line

Connecting to a Hotspot There are actually two steps to making a connection. The first is to have your notebook "talk" to the hotspot On the newest machines, an 802.11 card will automatically connect with an 802.11 hotspot and a network connection will be established.

Connecting to a Hotspot (Cont’d) On older machines you often have to go through a simple 3-step process to connect to a hotspot.

Connecting to a Hotspot (Cont’d) Access the software for the 802.11 card -normally there is an icon for the card down in the system tray at the bottom right of the screen. Click the "Search button" in the software. The card will search for all of the available hotspots in the area and show you a list. Double-click on one of the hotspots to connect to it.

Connecting to a Hotspot (Cont’d) On older machines you often have to go through a simple 3-step process to connect to a hotspot. Find what is the SSID of the hotspot All the search feature (in newer equipment) is doing is grabbing these two pieces of information from the radio signals generated by the hotspot and displaying them for you.

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

Connecting to a Hotspot (Cont’d) You can also see the quality of the signal by clicking on the radio icon (may vary by system):

Connecting to a Hotspot (Cont’d) Sign up with a wireless Internet service provider and configure your notebook according to their instructions. If you don't subscribe to a service, chances are you will need to use your credit card to pay for access every time you want to connect. After this, you will end up at the log-on page of the wireless provider (or, in some cases, the wireless location).

Connecting to a Hotspot (Cont’d) Enter your user name and password if you are already a customer. Once you successfully log on, you should see the following icon in your tool bar, indicating the connection has been made:

WiFi Security WiFi hotspots can be open or secure. If a hotspot is open, then anyone with a WiFi card can access the hotspot. If it is secure, then the user needs to know a WEP key to connect. WEP stands for Wired Equivalent Privacy

WiFi Security (Cont’d) WEP is an encryption system for the data that 802.11 sends through the air. Specifically, it is the process of encoding bit stream in such a way that only the person (or computer) with the key (a digital sequence) can decode it.

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

Setup #1

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

One Type of Amplifier Or a directional antenna can be used to give better range in a particular direction.

Another Way to Amplify WiFi Signals Wireless Access Point A WiFi repeater is installed to extend coverage.

Configuring a Hotspot Most wireless access points come with default values built-in. Once you plug them in, they start working with these default values. However, you may want to change things. You normally get to set three things on your access point.

Things to Configure in a Hotspot The SSID -- Service Set IDentifier is a sequence of charactersthat uniquely names a WLAN. The channel – the radio link used by access point/router to communicate to wireless devices. The WEP key -- The default is to disable WEP.

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

Advantages of Wi-Fi

Disadvantages Planning – Depending on the goal Security – Greater exposure to risks Access Compromising Data Denial of Service Speed – Slower than cable Range – Affected by various medium

Difference between Bluetooth and Wi-Fi

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