17-WirelessLANs2011.pptVIP

William StallingsData and Computer Communications7th Edition Chapter 17 Wireless LANs Overview A wireless LAN uses wireless transmission medium Used to have high prices, low data rates, occupational safety concerns, and licensing requirements Problems have been addressed Popularity of wireless LANs has grown rapidly Applications - LAN Extension Single Cell Wireless LAN Configuration Applications - LAN Extension Multi-Cell Wireless LAN Configuration Applications – Cross-Building Interconnect Connect LANs in nearby buildings Point-to-point wireless link Connect bridges or routers Not a LAN per se Usual to include this application under heading of wireless LAN Applications - Nomadic Access Link between LAN hub and mobile data terminal Laptop or notepad computer Enable employee returning from trip to transfer data from portable computer to server Also useful in extended environment such as campus or cluster of buildings Users move around with portable computers May wish access to servers on wired LAN Infrastructure Wireless LAN Applications – Ad Hoc Networking Peer-to-peer network Set up temporarily to meet some immediate need E.g. group of employees, each with laptop or palmtop, in business or classroom meeting Network for duration of meeting Add Hoc LAN Technology Infrared (IR) LANs: Individual cell of IR LAN limited to single room IR light does not penetrate opaque walls Spread spectrum LANs: Mostly operate in ISM (industrial, scientific, and medical) bands No Federal Communications Commission (FCC) licensing is required in USA Narrowband microwave: Microwave frequencies but not use spread spectrum Some require FCC licensing Spread Spectrum LANsHub Configuration Usually use multiple-cell arrangement Adjacent cells use different center frequencies Hub is typically mounted on ceiling Connected to wired LAN Connect to stations attached to wired LAN and in other cells May also control access IEEE 802.11 point coordination function May also act as multiport repeat