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WiFi part II

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  • Last Seminar we have seen multiple flavors of wifi. Those are……
  • We have seen their speed, range, frequencies.In today’s seminar we’ll see working of the wifi, its elemnts, communicaion in wifi, wifinetwrk topology.
  • • Wi-Fi cards - (e.g PCMCIA Card for Laptop and PCI Card for Desktop PC)
  • To understand the wire less technology let us consider a pair of Walkie-Talkies.These are small radios that can transmit and receive radio signals.When we talk into a Walkie-Talkie, our voice is picked up by a microphone, encoded onto a radio frequency and transmitted with the antenna. Another Walkie-Talkie can receive the transmission with its antenna, decode our voice from the radio signal and drive a speaker.Simple Walkie-Talkies like this transmit at a  signal strength of about 0.25 watts, and they can transmit about 500 to 1,000 feet.If we want to connect two computers together in a network using Walkie-Talkie technology:Equip each computer with a Walkie-Talkie.Give each computer a way to set whether it wants to transmit or receive.Give the computer a way to turn its binary 1s and 0s into two different beeps that the walkie-talkie could transmit and receive and convert back and forth between beeps and 1s/0s.This would actually work. The only problem would be that the data rate would be very slow. Walkie-talkie is designed to handle the human voice.So it is not being able to send very much data in this way(may  be 1,000 bits per second).                   
  • Lets seewifi’s radio technology
  • The most important items which makes Wi-Fi working in the laptop or desktop areRadio SignalsWi-Fi Card which fits in your laptop or computer.Hotspots which create Wi-Fi Network.
  • Antennas work stronger and have a longer radio transmission with a radius of 300-500 feet which are used in public areas while the weaker yet effective router is more suitable for homes with a radio transmission of 100-150 feet.
  • You can think WiFi card as being an invisible cord that connects your computer to the antenna for a direct connection to the internet.
  • Most hotspots are located in places that are readily accessible to the public, like airports, coffee shops, hotels, book stores and campus environments. 802.11b is the most common specification for hotspots worldwide. The 802.11g standard is backwards compatible with .11b but .11a uses a different frequency range and requires separate hardware such as an a, a/g, or a/b/g adapter. The largest public Wi-Fi networks are provided by private internet service providers (ISPs) that charge a fee for users to connect to the internet.
  • Data exchange in Wi-Fi can be summarized into three phases:Phase I: Where data is prepared for transmission; it is encoded; changed into frames (digital signals are sent in frames for better QoS). The frequency for data transmission is also chosen depending upon the technique used to send the signals wirelessly.Phase II: Where data is transmitted with air as the medium of wave transmissionPhase III: Where data is received, decoded, acknowledged and then used.All of these phases apply some of the popular digital communications spread spectrum techniques for signal multiplexing (FHSS, Infrared, OFDM etc.), make use of security methods (WEP, WPA). Let’s find out the technical insides of the Wi-Fi legacy.
  • Many new laptops come with a Wi-Fi card built in. It is also easy to add a Wi-Fi card to an older laptop or a desktop PC.  The process is
  • These are Wifi network topologies.
  • This is the graph of Hotels offering Wi-Fi . As you can see here


  • 1. 802.11 Technology Shital Katkar Old Roll No – 51 New Roll No - 05
  • 2. Flavours of WIFI  IEEE 802.11 b (1999)  IEEE 802.11 a (2001)  IEEE 802.11 g (2003)  IEEE 802.11 n (2009)
  • 3. Flavours of WIFI
  • 4. Elements of a WI-FI Network  • Access Point (AP) - The AP is a wireless LAN transceiver or “base station” that can connect one or many wireless devices simultaneously to the Internet.  • Wi-Fi cards - They accept the wireless signal and relay information. They can be internal and external.  • Safeguards - Firewalls and anti-virus software protect networks from uninvited users and keep information secure.
  • 5. Wi-Fi’s Walkie-Talkie Network
  • 6. Wi-Fi's Radio Technology:  WiFi radios that work with the 802.11b and 802.11g standards transmit at 2.4 GHz, while those that work with the 802.11a standard transmit at 5 GHz. Normal walkie-talkies normally operate at 49 MHz. The higher frequency allows higher data rates.  WiFi radios use much more efficient coding techniques that also contribute to the much higher data rates. For 802.11a and 802.11g, the technique is known as orthogonal frequency-division multiplexing (OFDM). For 802.11b, it is called Complementary Code Keying (CCK).
  • 7. Wi-Fi's Radio Technology:  The radios used for WiFi have the ability to change frequencies. 802.11b cards can transmit directly on any of three bands, or they can split the available radio bandwidth into dozens of channels and frequency hop rapidly between them. The advantage of frequency hopping is that it is much more immune to interference and can allow dozens of WiFi cards to talk simultaneously without interfering with each other.
  • 8. Working
  • 9. Radio Signals:  Radio Signals are the keys which make WiFi networking possible. These radio signals transmitted from Wi-Fi antennas are picked up by WiFi receivers such as computers and cell phones that are equipped with WiFi cards. Whenever a computer receives any of the signals within the range of a WiFi network which is usually 300 - 500 feet for antennas, the WiFi card will read the signals and thus create an internet connection between the user and the network without the use of a cord.  Access points which consist of antennas and routers are the main source which transmit and receive radio waves.
  • 10. Wi-Fi Cards:  WiFi cards can be external or internal, meaning that if a WiFi card is not installed in your computer, you may purchase a USB antenna attachment and have it externally connect to your USB port, or have an antenna-equipped expansion card installed directly to the computer. For laptops, this card will be a PCMCIA card in which you insert to the PCMCIA slot on the laptop.
  • 11. Wi-Fi Hotspots:  A Wi-Fi hotspot is created by installing an access point to an internet connection. The access point transmits a wireless signal over a short distance . typically covering around 300 feet. When a Wi-Fi .enabled device, such as a Pocket PC, encounters a hotspot, the device can then connect to that network wirelessly.
  • 12. Communication in Wi-Fi
  • 13. Adding WiFi to a Computer  Take a 802.11a, 802.11b or 802.11g network card. 802.11g has the advantage of higher speeds and good interoperability on 802.11b equipment.  For a laptop, this card will normally be a PCMCIA card that slide into a PCMCIA slot on laptop. Or take a small external adapter and plug it into a USB port.  For a desktop machine, take a PCI card & install inside the machine, or a small external adapter and connect to the computer with a USB cable.  Install the card  Install the drivers for the card  Find an 802.11 hotspot  Access the hotspot.
  • 14. Wi-Fi Network Topologies  • AP-based topology (Infrastructure Mode)  • Peer-to-peer topology (Ad-hoc Mode)  • Point-to-multipoint bridge topology
  • 15. AP-based topology     • The client communicate through Access Point. • BSA-RF coverage provided by an AP. • ESA-It consists of 2 or more BSA. • ESA cell includes 10-15% overlap to allow roaming.
  • 16. Peer-to-peer TOPOLOGY  AP is not required.  • Client devices within a cell can communicate directly with each other.  • It is useful for setting up of a wireless network quickly and easily.
  • 17. Point-to-multipoint bridge TOPOLOGY  This is used to connect a LAN in one building to a LANs in other buildings even if the buildings are miles apart. These conditions receive a clear line of sight between buildings. The line-of-sight range varies based on the type of wireless bridge and antenna used as well as the environmental conditions.
  • 18. Conclusion  Wi-fi is a simple, cost-effective way to connect to the Internet , Without the need to physically connecting wires.  Hotspot s a geographic area setup in any public location, and has a readily accessible wireless network  Security is a huge challenge for Wi-Fi Networks, many Security Techniques are used to improve it.
  • 19. The Future of Wi-Fi  The future of Wi-Fi is very bright. Its growing in popularity because of decreasing cost and the freedom it gives to users.
  • 20. Reference  802.11ac: The Fifth Generation of Wi-Fi Technical White Paper  http://www.cisco.com/en/US/prod/collateral/wireless/ ps5678/ps11983/white_paper_c11-713103_ns767_Networking_Solutions White_Paper.html  http://www.essaytown.com/paper/shared-wireless-wireless-fidelity-wi-finetwork-term-35660  Impact of wireless technology  http://www.studymode.com/essays/Impacts-Of-Wireless-FidelityTechnology-214064.html
  • 21. Thank You 