《计算机科学导论》课件Unit 6Computer Networks知识介绍.pptVIP

* Mobility becomes another issue. If a mobile client is moved away from the access point it is using to another; there must be some way of handing it off. The solution is that an 802.11 network may include multiple cells, each with its own access point, and a distribution system that links all the cells. We often use switched Ethernet【交互式以太网】to realize the distribution system, but other technology may be used for it. When the mobile clients move, they can use other access point with a better signal to replace the original access point and shift their association. As a whole, we can consider the entire system as a single wired LAN【单一的有限局域网】. Finally, there come security issues. Since wireless networks broadcast transmissions, so nearby device users who want to get the information can easily receive the packets not intended for them. LANs Wireless * In order to stop this situation, a well-known encryption scheme named as WEP (Wired Equivalent Privacy) 【有线等效必威体育官网网址】 was assigned to the 802.11 standard. The aim of this was to make the wireless security same as the wired security. With the development of technology, WiFi Protected Access【无线保护访问】, initially called WPA, but now upgraded to WPA2, has replaced the old schemes. The 802.11 standard is a revolution in wireless networking. Beyond buildings, it can be used in trains, planes, boats, and automobiles. People are able to surf the Internet whenever they want or wherever they go. ZigBee technology 【紫蜂技术】is one of the most important wireless network standard. The characteristics of ZigBee are short transmission distance, low power consumption, low speed, low complexity, and low cost. It can help mobile phones and all manner of consumer electronics, from game consoles to digital cameras, to communicate more easily. LANs Wireless * Repeaters Bridges Switches Routers Gateways 6-3 Devices in Networks * Devices in Networks Nowadays there are a lot of connecting devices to connect different networks. However, connecti