数据与计算机通信17-WirelessLANs.pptVIP

William StallingsData and Computer Communications7th Edition Chapter 17 Wireless LANs 17.1 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 17.1.1 Applications - LAN Extension Saves installation of LAN cabling Eases relocation and other modifications to network structure However, increasing reliance on twisted pair cabling for LANs Most older buildings already wired with Cat 3 cable Newer buildings are prewired with Cat 5 Wireless LAN to replace wired LANs has not happened In some environments, role for the wireless LAN Buildings with large open areas Manufacturing plants, stock exchange trading floors, arehouses Historical buildings Small offices where wired LANs not economical May also have wired LAN Servers and stationary workstations Single Cell Wireless LAN Configuration单蜂窝 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本质上 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自组网络 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自组局域网 17.1.2 Wireless LAN Requirements（1） Same as any LAN High capacity, short distances, full connectivity, broadcast capability Throughput: efficient use