tailieunhanh - cwna certified wireless network administrator official study guide phần 3

Các quy định của FCC về việc sử dụng trải phổ rất rộng, cho phép cho các loại khác nhau triển khai thực hiện phổ lây lan. Một số hình thức của quang phổ lan truyền giới thiệu các khái niệm về tần số nhảy, có nghĩa rằng các hệ thống truyền và nhận hop từ tần số với tần số trong một dải tần số truyền dữ liệu khi họ đi. | 49 Chapter 3 - Spread Spectrum Technology Wireless Personal Area Networks Bluetooth the most popular of WPAN technologies is specified by the IEEE standard. The FCC regulations regarding spread spectrum use are broad allowing for differing types of spread spectrum implementations. Some forms of spread spectrum introduce the concept of frequency hopping meaning that the transmitting and receiving systems hop from frequency to frequency within a frequency band transmitting data as they go. For example Bluetooth hops approximately 1600 times per second while HomeRF technology a wide band WLAN technology hops approximately 50 times per second. Both of these technologies vary greatly from the standard WLAN which typically hops 5-10 times per second. Each of these technologies has different uses in the marketplace but all fall within the FCC regulations. For example a typical frequency hopping WLAN might be implemented as an enterprise wireless networking solution while HomeRF is only implemented in home environments due to lower output power restrictions by the FCC. Wireless Metropolitan Area Networks Other spread spectrum uses such as wireless links that span an entire city using high-power point-to-point links to create a network fall into the category known as Wireless Metropolitan Area Networks or WMANs. Meshing many point-to-point wireless links to form a network across a very large geographical area is considered a WMAN but still uses the same technologies as the WLAN. The difference between a WLAN and a WMAN if any would be that in many cases WMANs use licensed frequencies instead of the unlicensed frequencies typically used with WLANs. The reason for this difference is that the organization implementing the network will have control of the frequency range where the WMAN is being implemented and will not have to worry about the chance of someone else implementing an interfering network. The same factors apply to WWANs. FCC Specifications .