TAILIEUCHUNG - Lecture Wireless LANs: Exploring Wireless Networking

After studying this chapter you will be able to: Describe wireless LAN technology and standardsm, describe the components of a wireless LAN infrastructure, describe wireless topologies, describe the frame structure,.and another content. | Wireless LANs Exploring Wireless Networking Market Trends People are no longer restricted to traveling to fixed work location for defined periods of time for productivity. People are now expecting to be connected at any time at any place. This change in environment reaches far from the office to many location such as airport or even the home. Traveling employees used to be restricted to pay phones for checking messages and returning a few phone calls between flights. Now employees can check email, voice mail, and the web status of products on PDAs while walking to the flight. Even at home people have changed the way they live and learn. The internet has became more of a standard at homes along side of TV and phone service. Even the method of accessing the Internet has quickly moved from temporary modem dial service to dedicated DSL or cable service that is always connected and with greater speed. More recently during 2005 users of PCs are purchasing more Wi-Fi enabled mobile laptops instead of a fixed location desktop. Differences Between WLAN and LAN WLANs use radio waves as the physical layer. WLANs use CSMA/CA instead of CSMA/CD for media access. Two-way radio (half-duplex) communication. Radio waves have problems that are not found on wires. Connectivity issues: Coverage problems Interference, noise Privacy issues Access points are shared devices similar to an Ethernet hub for shared bandwidth. WLANs must meet country-specific RF regulations. Following is an explanation of how WLANs differ from LANs. -> In WLANs, radio frequencies are used as the physical layer of the network. - WLANs use CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) instead of CSMA/CD (Carrier Sense Multiple Access with Collision Detection) that is used by Ethernet LANs. Collision detection is not possible because a sending station cannot receive at the same time that it is transmitting and, therefore, cannot detect a collision. Instead, the Request to Send (RTS) and Clear .

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