1. 802.11 Wireless LANs Wireless Technologies for LANs –Radio –Infrared light (as in TV remote control) –Ideal for mobile devices –Useful when wiring would be costly

2. 802.11 Wireless LAN Standards Standards come from the 802.11 Working Group –Initially, 1 Mbps and 2 Mbps standards for radio –Too slow for wide acceptance –Now, 11 Mbps –Prices falling but still high –On positive side, avoids the labor cost of installing wiring

3. 802.11 Wireless LANs Normally use an Access Point –Bridges wireless device to server on main wired LAN Box about the size of a hard cover book Access Point UTP RJ-45 Port Switch Or Hub Server

4. 802.11 Wireless LANs Ad Hoc Mode –Clients and servers communicate directly –Good for wireless conference rooms –Not scalable Server

5. 802.11 Wireless LANs Media Access Control (CSMA/CD+ACK) –CSMA/CA –CSMA with Collision Avoidance Tries to avoid collisions –When line is clear, station may send (CSMA), –but before it sends, must wait a random amount of time –This prevents stations that have been waiting to transmit from all transmitting at once when the currently transmitting station is finished

6. 802.11 Wireless LANs Media Access Control –When a frame is received correctly, the receiver immediately sends back an acknowledgement –This allows the sender to know if it needs to resend Frame ACK

7. 802.11 Versus Bluetooth 802.11 –Designed for site radio LANs Bluetooth –Created by an industrial consortium –Designed to link nearby objects (within a few meters) –Personal area networking (cellphone, computer, printer, etc.)

8. 802.11 Versus Bluetooth Bluetooth –721 kbps transmission speed 56 kbps back channel –Up to 10 piconets in an area Each with a maximum of eight devices –Named for King Harald Bluetooth who unified Denmark and Norway in the 10th Century

9. 802.11 Versus Bluetooth Possible Interference –802.11 and Bluetooth use the same frequency band –May interfere if they are active in the same area –801.15 Working Group is working on coexistence methods

10. Radio LANs Radio Propagation Problems –Shadow zones where signal does not reach –Multipath transmission, in which signals traveling different paths interfere with one another Shadow Zone Multiple Paths