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Điện thoại di động mạng lưới Radio P13

Wireless Local Area Networks∗ Since the introduction of lightweight portable computers (laptops, notebooks), a great deal of attention has been focused on the development of wireless computer networks (Wireless Local Area Network, WLAN). Thanks to standardization in the field of local area networks, it is comparatively easy to find systems that will still be upgradable even in a few years’ time. Around 70 % of all computers connected to networks are compliant with the IEEE 802.3 (Ethernet) and IEEE 802.5 (Token Ring) standards. Connection is normally over a permanent wireline link | Mobile Radio Networks Networking and Protocols. Bernhard H. Walke Copyright 1999 John Wiley Sons Ltd ISBNs 0-471-97595-8 Hardback 0-470-84193-1 Electronic 13 Wireless Local Area Networks Since the introduction of lightweight portable computers laptops notebooks a great deal of attention has been focused on the development of wireless computer networks Wireless Local Area Network WLAN . Thanks to standardization in the held of local area networks it is comparatively easy to find systems that will still be upgradable even in a few years time. Around 70 of all computers connected to networks are compliant with the IEEE 802.3 Ethernet and IEEE 802.5 Token Ring standards. Connection is normally over a permanent wireline link. The problems that can occur are the surfacing of mechanical defects corrosion after a few years and violations of rules on radiated interference. It is difficult to adapt these networks to cope with changing office conditions. Mobile network nodes are not possible. The obvious approach is to leave out the cable entirely. This idea is almost as old as the concept of the so-called ALOHA system which used radio to connect terminals to their processing computers. The newer wireless LANs work with the most up-to-date radio technology. Data is encrypted and extensive error-protection mechanisms are available. Integrity of data is also guaranteed. Just like wireline LANs wireless LANs can be divided into different architectures and performance categories. Many companies offer products for wireless point-to-point connections but only very few build LANs for multipoint communication. Today wireless networks use spread-spectrum narrowband microwave or infrared signals for transmission see Table 13.1 . Because of legal regulations networks using spread-spectrum and narrowband microwave cannot be operated in most countries unless special authorization has been given. Until now wireless LANs have only had a very small share of the market. This is partly due to