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cwts certified wireless technology specialist official study guide exam pw0 070 phần 5

thiết bị mạng LAN không dây sử dụng giao tiếp half-duplex. Song công một nửa được định nghĩa là giao tiếp hai chiều chỉ có một cách tại một thời điểm. Có dây mạng LAN có thể sử dụng full-duplex truyền thông, mà là hai chiều thông tin liên lạc truyền theo cả hai hướng cùng một lúc. | Answers to Review Questions 157 Answers to Review Questions 1. C. IEEE wireless LAN devices use half-duplex communication. Half duplex is defined as two-way communication only one way at a time. Wired LANs can use full-duplex communication which is two-way communication transmitting in both directions simultaneously. An example of diplex is to combine signals from two different frequencies into a single transmitter receiver. 2. A. DSSS devices operate in the 2.4 to 2.5 GHz ISM band. OFDM devices operate in the 5GHz UNII bands. 3. B. 802.11b operates in the 2.4 GHz ISM band. A total of three access points can be co-located before interference becomes an issue. 4. D. The IEEE 802.11n draft 2.0 amendment devices use MIMO multiple radio chains and antennas to operate. 802.11a b g devices use one radio and may use multiple antennas for diversity. 5. C. Spread spectrum technology sends data over many subcarrier frequencies. Narrowband technology is not used in IEEE-based WLANs but is used in other technology such as radio and TV. Wireless broadband provides high-speed wireless data communications and wireless internet over a wide area network. Wideband uses a wide range of frequencies and spectral mask refers to the signal levels of the radio frequency. 6. B C D. 802.11b channels need to be separated by at least five channels or 25 MHz to be considered non-overlapping. Channels 3 and 9 are separated by six channels channels 6 and 11 are separated by five channels and channels 2 and 8 are separated by six channels. All of these scenarios are non-overlapping channels. 7. A. CSMA CA uses collision avoidance. CSMA CD uses collision detection. CSMA CR and CSMA DSSS do not exist. 8. A. DSSS uses Barker code at 1 Mbps. CCK is for 5.5 Mbps. DBPSK and DQPSK are modulation technologies not spreading codes. 9. A. FM radio stations use narrowband communication which is high power and narrow frequency. WLANs use spread spectrum technology which is low power and wide frequency. 10. C.