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Bluetooth When you use computers, entertainment systems or telephones, the various pieces and parts of the systems make up a community of electronic devices. These devices communicate with each other using a variety of wires, cables, radio signals and infrared light (红外线) beams, and an even greater variety of connectors and plugs. The art of connecting things is becoming more and more complex every day. And Bluetooth has now become a new popular method of connecting devices that can streamline the process. A Bluetooth connection is wireless and automatic, and it takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power. Bluetooth Operation Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (千兆赫) (actually between 2.402 GHZ and 2. 480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM). A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors (微型监视器), garage-door openers and the newest generation of cordless phones (无绳电话) all make use of frequencies in the ISM band. One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The wall in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms. Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread- spectrum (扩展频谱) frequency that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter (传输设备) uses spread-spectrum transmitting automatically, it's unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second. Piconets (个人域网络) Let's say you have a typical modern living room with the typical modern stuff inside. There's an entertainment system with a stereo, a DVD player, a satellite TV receiver and a television there's also a cordless telephone and a personal computer. Each of these systems uses Bluetooth, and each forms its own piconet to talk between the main unit and peripheral (外围设备). The cordless telephone has one Bluetooth transmitter in the base and another in the handset. The manufacturer has programmed each unit with an address that falls into a range of addresses it has established for a particular type of device. When the base is first turned on, it sends radio signals asking for a response from any units with an address in a particular range. Since the handset has an address in the range, it responds, and a tiny network is formed. Now, even if one of the
A.
Y
B.
N
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NG
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【简答题】为人民服务是( ) A是社会主义道德体系原则 B社会主义道德规范 C家庭道德的具体要求 D社会主义职业道德核心规范
【简答题】. 简述教师威信维护的策略
【单选题】社会主义道德的原则是( )
A.
为人民服务
B.
集体主义
C.
爱国主义
D.
共产主义
【简答题】简述教师威信的维护。
【简答题】工资管理系统传递到总账中的凭证,在工资管理系统中可以进行__ __。
【单选题】发生网络安全事件时,应当()启动网络安全事件(),并及时向社会发布与公众有关的警示信息。
A.
立即、风险预案
B.
立即、应急预案
C.
尽快、应急预案
D.
尽快、风险预案
【单选题】发生网络安全事件,应当立即启动网络安全事件应急预案,对网络安全事件进行(),要求网络运营者采取技术措施和其他必要措施,消除安全隐患,防止危害扩大,并及时向社会发布与公众有关的警示信息。
A.
调查和评估
B.
调查
C.
评估
D.
分析
【简答题】简述教师威信的维护和发展?
【单选题】发生网络安全事件,应启动()。
A.
网络安全等级保护制度
B.
网络安全举报制度
C.
网络安全审查制度
D.
网络安全事件应急预案
【单选题】发生网络安全事件,应启动( )。
A.
络安全等级保护制度
B.
网络安全举报制度
C.
络安全审查制度
D.
网络安全事件应急预案
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