Introduction to information technology [Introduction to information technology] Introduction to Bluetooth technology: Bluetooth technology is a short-distance, low-power wireless communication standard, which provides a low-cost wireless networking method for devices. This paper introduces the underlying module, protocol and application model of Bluetooth technology, and compares it with other commonly used wireless connection technologies to illustrate its advantages. Keywords: Bluetooth; Bottom module; Agreement; Application As early as 1994, Ericsson put forward a research plan within it, aiming at establishing and developing a new generation of wireless transmission technology that can be easily used and unimpeded on various communication devices, and establishing practical wireless interfaces and related software standards. 1998, Ericsson announced this plan, and formed a special interest group with Nokia, IBM, Toshiba and Intel to be responsible for the development of this technology. One year later, in July, 1999, SIG formally proposed the technical protocol of 1.0 version, and named the technology Bluetooth. According to the official interpretation of SIG, the name Bluetooth comes from harald Bluetooth, the Viking king of Denmark in the 10 century. The king unified Denmark and Norway by force and established a huge empire in Scandinavia. Bluetooth technology solves the problem of wireless interconnection between small mobile devices. Its hardware market is very broad, covering all kinds of data and voice equipment in LAN. The essential purpose of this technology is not to become another wireless LAN technology, but to become a new wireless solution to replace transmission cables. From the version of 1.0 of 1999 to the later versions of 1. 1, 1.2 and 2.0, Bluetooth technology has been constantly improving itself in technology, trying to absorb the advantages of general cables in terms of cost, safety and carrying capacity. After the Bluetooth King dominated Northern Europe for thousands of years, the emerging Bluetooth technology is opening up a territory thousands of times larger than the Bluetooth King in the global wireless connection market with its various advantages. 2. Overview of Bluetooth Protocol The protocol model in Bluetooth architecture can be divided into the following five layers: physical layer: wireless interface layer of Bluetooth protocol; Core protocols: baseband protocol, link management protocol, logical link control and adaptation protocol, service discovery protocol, etc. Baseband protocols can provide synchronous connection-oriented services and asynchronous connection services. Generally speaking, SCO is used for packet data service, which is characterized by reliability but delay; ACL is used for voice transmission, which is characterized by good real-time performance. But the reliability is worse than SCO. Link management protocol is responsible for establishing and releasing the connection between master and slave equipment units, and controlling the working mode of master and slave equipment units. L2CAP is the third layer control and adaptation protocol, which provides connection-oriented and connectionless services for layers such as RFCOMM and SDP. Baseband data services can directly transmit data to higher layer protocols through LMP and L2CAP. In a sense, both L2CAP and LMP are equivalent to the second layer protocol of OSI, that is, the link layer. Radio frequency communication protocol: RFCOMM, which can simulate the serial cable interface protocol. Through RFCOMM, Bluetooth can support high-level protocols such as PPP, TCP/IP and WAP in wireless environment. RFCOMM can support AT command set and realize wireless connection of mobile phone, fax machine and modem; Telephone transmission control protocols: TCS binary protocol, AT command set, etc. Application protocols: PPP, UDP/TCP/IP, OBEX, vCard/vCarl, fax, PAN, etc. 3. Bluetooth bottom module Bluetooth bottom module is the core of Bluetooth technology, and it is a necessary part of any Bluetooth device. In order to ensure that the frequency band required by the system can be easily obtained around the world, the Bluetooth system works at the industrial, scientific and medical frequency of most countries, that is, 2.4GHz. Due to the openness of the ISM frequency band, the use of any frequency band will encounter unpredictable interference-for example, wireless phones and microwave ovens at home may become interference sources. For this reason, Bluetooth has specially designed a fast acknowledgement and frequency hopping scheme to ensure the stability of the link. Bluetooth divides its working frequency band from 2.402 GHz to 2.480 GHz into 79 subchannels with a bandwidth of 1MHz, and jumps to another frequency after receiving or sending a packet of data, thus enhancing the stability of data transmission. Frequency hopping technology not only ensures the stability of Bluetooth technology, but also ensures its security in the physical layer. In frequency hopping communication, data signals are modulated by narrowband carrier signals, and these narrowband carrier signals constantly jump from one frequency to another as a function of time. The Bluetooth standard uses a frequency hopping sequence of 1600 hops per second. The frequency hopping code known to both transmitter and receiver determines the frequency of RF carrier and the order of frequency hopping. In order to receive the signal correctly, the receiver must set the same frequency hopping code as the sender, and monitor the carrier signal at the right time and frequency. Only when the synchronization is correct can the logical channel be maintained. The signals received by other asynchronous receivers are only impulse noise with very short duration, so eavesdropping is very difficult. The third advantage of frequency hopping technology is that multiple devices can be connected at the same time. As mentioned earlier, Bluetooth operates in frequency hopping mode in 79 channels. When two Bluetooth devices successfully establish a link, a piconet is formed. The communication between them is completed by radio waves jumping randomly in these 79 channels. Bluetooth provides a specific hop mode for each piconet, so it allows a large number of piconets to exist at the same time. 3.2 Duplex Mode and Service Type
Is introduction to information technology a water course? Introduction to information technology is a professional introductory course, which aims to make students have a deep understanding of the development history, basic principles and practical technology of this subject without involving too much professional knowledge. Water course refers to a boring and uninteresting course, so the introduction to information technology is not a water course, but a compulsory course for majors and computers.
Is the teaching material for self-taught accounting major the same as that for unified recruitment? The self-taught textbooks for accounting majors are the same as those for unified recruitment. The content is similar, the depth of unified recruitment is more difficult, and the teaching materials for self-study are slightly simpler. 1. The self-study exam is relatively loose and strict, and the undergraduate students recruited by the state need to take the college entrance examination and score online before they can be admitted ~! 2. Self-taught undergraduate students have to pass about 33 courses to get a diploma! Unified recruitment means going to school, attending classes, being taught by teachers, and the examination papers for unified recruitment are generally issued by schools, which are relatively easy to test. 3. Most of the self-taught candidates are self-taught while working, with no classes and no teachers. If you take the self-taught exam, it is basically a national unified exam paper, which is more difficult to take.
After the introduction of nursing education, it is necessary to look at the introduction of nursing. I am a self-taught college for nursing majors. As long as the subject code is the same, I don't have to take the exam again. In 2009, Henan self-taught nursing examination plan examiner school: Zhengzhou University examination form: entrusted examination serial number
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1 03708 Outline of Modern History of China 22 03709 Introduction to Basic Principles of Marxism 43 000 15 English 144 000 18 Computer Application Foundation 25 000 19 Computer Application Foundation 26 03200 Preventive Medicine 67 0320/kloc. Introduction to Nursing 5 8 03202 Internal Medicine Nursing 59 03203 17 03005 Introduction to Nursing Education 5 18 07277 Clinical Examination 0 19 06999 Graduation Thesis 0 is not counted as credits.
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