Networked control

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Network control refers to the access information for modern communications technology.

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Keywords or Keywords: Information Science Communication

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Introduction of documents into the file communication Network communication (communication is its former name), as the name implies access information. Although it has not yet been given an exact and accepted definition of what is information, the flowability of information has become the consensus of the people. The value of information lies in the flow, only to flow together to share for all. In other words, the information itself does not show value, only through the transmission can produce its effectiveness. According to the economic point of view, information flow is the multiplier factor of national economic development. It can be expressed by the following formula: social net output = total input of material production (including manpower and capital) information flow As mentioned before, according to information theory, The complete information system consists of three parts: "source", "channel" and "sink". Any information always has a birthplace and destination, such as Lee four to Zhang three informed an important information, then, John Doe is the source of information, called the "source"; Zhang is the destination of information, called " ; Li four and Zhang three information transmission channel called "channel". In the source, channel and sink three elements, the source and sink can be a mutual translocation. Party A and Party B make phone calls, Party A's information is the source of the message, Party B received the information from Party A is a but when Party B according to Party B information to feedback, Party B became a letter Source, Party A Party B to accept the feedback information, this time into a letter places, so endless. However, as the bridge between the source and the sink - channel, it is relatively unchanged. Information can be circulated, but the content of information must be reflected in a certain form, this is the "signal." In other words, information is passed through a certain signal, the signal plays the role of information carrier. The source of information, the signal is generally expressed in some way, there are electrical signals as the carrier, such as wire communication, radio communication, there are optical signals for the carrier, such as wireless optical communications (atmospheric laser communication) Wired optical communication (optical fiber communication) and the like. The same information can be expressed in the form of a language (such as a telephone message), can also be used characters (letters, numbers and symbols collectively), the image of the expression (such as telegraph, fax machine to transfer information) Into electronic computer code. In addition, the information sent by the source can be compressed in a very short time fast transfer, can also be reduced to a small space within the first store up. Information transmission system in the source, channel and sink elements and transportation systems and vehicles in the road a bit similar. Transportation in the process of loading and unloading, information transmission also has "loaded" and "unloading" problem. "Loading" is to transform the information to be transmitted into a suitable channel for the signal "unloading" refers to the signal sent from the channel into the letter can be received form. In the information system, the former is called "encoding", the latter is called "decoding". For example, the transmission of a telegram, the sender (source) first intended to express their intended message, the message by the operator through the machine or button to convert the code, which is "coding", where the "code" Refers to the rules in accordance with a certain arrangement of the symbol sequence, after encoding, messages (information) to evolve into a signal. In the actual information transfer process, the information is often to be encoded several times before being sent to the channel transmission. After the code signal is transmitted to the receiving end through the channel, the receiving and receiving person first receives the electric signal, and then the electric code is reduced to the message, this is the "decoding". Decoding is actually the inverse transformation of the code, after transformation, so that the receiver (destination) to understand the sender to express the meaning of this is the process of telegraph transmission of information. Not only telegraph so, all the information transfer process is an exception, but the specific source, channel, destination, and coding, decoding methods may be different. (Such as lightning), there are interference from the information system (such as thermal noise, etc.), but also from the outside of the information system (such as lightning), there are interference from the information system (such as thermal noise), but also from outside the information system Of the interference, so that the original letter can not be the original, accurate and accurate information received from the source, resulting in transmission quality degradation. Serious, the information is completely annihilated by the noise noise, so that information transmission can not be carried out. Therefore, how to combat noise with noise becomes an important issue in the transmission of information. In order to make the original information can be reproduced without distortion from the code sequence, the filter theory is put forward in the information theory research to minimize the information ambiguity. The so-called "filter", in layman's terms, refers to the obtained signal and interference of the composite wave, as far as possible interference wave filter removed, separated from the desired information. This is somewhat similar to the filter cigarettes that filter out harmful nicotine. As already mentioned, the transmission of information can not be separated from the channel, telegraph, telephone just came out, is to take through the establishment of a dedicated circuit method, the communication between the two sides. With the increasing number of communication users, this direct connectivity method is increasingly exposed to its drawbacks. We know that two telephones (telegraph) to have a pair of lines connected to the call (you can also use a line connected to the other line to the earth for the loop). If there are more than two telephone lines connected to the same one, you need to provide a different call otherwise, a rattling, we will come out should be. In practice, it is possible to connect two telephones directly (this is called a "straight-through private telephone") by directly using a pair of lines (usually one line for drawing). However, as the number of telephone users increases, Directly connected methods will be a problem. It is not difficult to see that the two users need one on the three users need three on the four users need to connect six pairs of lines ... ... If there are N communication between the users through each other, according to mathematical combination principle , Each user to connect the line need to line. For example, there are 5 users, you need to = 10 on the If N = 8, you need to = 28 on the Assuming the user to 1000, the total need to connect 499500 pairs of lines. N increases again, the required line will increase dramatically. Furthermore, when N is large, it is inconvenient for each telephone to connect (N-1) to the line, to be connected, to be installed and used. Obviously, the use of eleven direct connectivity is not feasible. If a telephone exchange is set at the center of the telephone subscriber distribution area, each telephone user pulls one wire to it, and the two users to be connected by the switch are temporarily connected so that only a total of N pairs of lines (radiation connection The number of lines is equal to the number of users) can be completed between any two users of the call connection, while other users do not access. Communication is a cross-regional, cross-sectoral, people always want to within a certain range of all communication points can be any communication between, which requires scattered around the switches are connected to each other to form a network of communication networks.

Communication network type / networked control editing

A wide range of communication networks, different structures. In the actual communication, the most simple communication network ring, grid, mesh and star-like and so on. Ring-shaped also called lattice form. A, B, C, D between the long-distance telephone offices have established a direct circuit (called dots connected), the middle does not need to go through transfer. When there is any circuit in which an obstacle, as long as a third party after a turn, you can create a circuitous communication. For example, a long-distance direct inter-circuit break, you can B or C long-distance telephone exchange, if necessary, can also be B and C through the two long-distance telephone Bureau joint transfer. The establishment of ring-type communication network, the advantage of rapid succession, high reliability. The disadvantage is that when the communication traffic is low, the circuit utilization is low. Therefore, it is generally suitable for communication between traffic points between the use of large. If on the basis of the ring network, any diagonal connection between the circuit, it becomes a grid if two diagonal lines are established between the direct circuit to form a mesh network . A star network, also known as a radiation network, radiates to other communications branches, centered around a communications office (often referred to as a switching center). Between the central offices in accordance with the ring-type network, there is no direct circuit between the communication bureau, must be transferred through the central office. No. 1 telephone communication network in the jurisdiction of the telephone number 1 users, if you want to find this network in the No. 4 Telephone Bureau under the jurisdiction of the user calls, as long as the central office after a transfer can if the telephone network with 4 In the user's call, you need to B and then by the Central Bureau of the C and other long-distance telephone exchange. The establishment of star-shaped communication network, the advantage is to save transmission lines, equipment and investment, communication network in any two users with the help of the Central Bureau of the transfer, you can always reach the communication, suitable for long-distance telephone traffic is relatively small, Wide area for use. However, because of this network structure with particular emphasis on the role of the central office of the network, once the central office of the obstacles, because there is no circuitous circuit, often leading to rudderless and affect the whole network communication. Said the above two kinds of networking methods in the function of their strengths, there is also a short director. In order to set the two excellent, in the organization of communication networks appeared on the integrated (also called convergence of radiation) communication network. Tandem radiation network has both the function of ring network, but also the characteristics of star-shaped network. In the area of less traffic using relay transfer, in the area of large traffic set up direct circuit. In order to enhance the reliability and flexibility of the communication network and improve the utilization efficiency of the transmission channel, it can cover long-distance communication in a large area. At present, the tandem of the domestic and foreign integrated communication network is usually multi- Four or even five) structure. A tandem center is a national center tandem two tandem centers and between each other and with a tandem center link between the ring, the establishment of direct long-distance telephone three tandem center and two Tandem Center, as well as the three tandem centers are usually established between the long-distance direct four tandem center is usually the Department of the tandem bureau, and tandem bureau has built a long-distance direct Then the convergence of the last level is usually the Department of tandem, generally by radiation type network. Multistage Tandem Radiocommunication Communication Network Because of the large communication coverage, users in any area of the network can find distant user calls. However, as the distance increases, the number of telephone calls increases accordingly Bale. With the development of science and technology, communication means more and more. In addition to the general telephone and telegrams, office automation systems such as mobile telephones, paging telephones, TV telephones, telex telegrams, image telegrams, facsimile, data services, and integrated terminal equipment are likely to emerge. In the future, New breakthrough. If the world as a large system, then the distribution of cities around the world is one of the information processing center, and support the information center is a variety of telecommunications networks. Advanced and efficient long-distance communication network is an important factor in the completion of information transmission. At present, some developed countries have basically eliminated the artificial connection network, and the use of automatic switching network to replace. Long-distance communication network in the past are used analog, and now has gradually to the digital direction (or digital-analog compatible). Integrated Services Digital Communication Network (ISDN) has been regarded as the development direction of communication network construction. It can be used not only for telephone communication but also non-telephone signals (such as documents, charts and computer data), telegraph, facsimile, Television, data transmission and other communications services. In the integrated services digital communications network, the transmission and exchange of signals are discrete digital signals, the equipment needs to use digital equipment, if the analog telephone needs to be transmitted or exchanged, you must go through the "analog / digital" conversion equipment A / D) to convert it into a digital signal before entering the network, to reach the receiving terminal, and then by the "digital / analog" conversion equipment (D / A) into the original analog telephone signal. With the increasing exchange of information, the establishment of a comprehensive utilization of wired and wireless communication network has been referred to the agenda, when the cable channel obstruction, the information will automatically be diverted, with wireless channel to replace the transmission.

Automatic Communication Integrated Network / Networked Control Editing

At present, foreign use of more "automatic communication integrated network" is an ideal of a telecommunications network. The network consists of three interconnected parts: the telephone backbone network, the wireless telephone network and the control center. Its main advantage is reliable communication, to ensure that users at any time with any other users to get in touch with mobility, when it will not interrupt the transfer of installation speed, the establishment of a telephone center only half an , When a part of the communications equipment is subject to accidental destruction or interference, the transmission of information will automatically roundabout to ensure uninterrupted communication. With the increasing friendly exchanges between countries around the world, communication has crossed the door to reach the world. To make the flow of information throughout the Wuzhou universal, as long as the integrated telephone communication network based on the use of various channels (satellite communications, optical communications, cable communications, etc.) will be a national tandem center link between each other, can set up a Global communications network, the huge blue planet in the communications giant network coverage. As long as you have a telephone, through the international long-distance direct dial telephone communication network, you can quickly and exotic relatives and friends in the call, make international calls as easy to play the city as the phone. "Memory of the sea friends, Tianya if adjacent," this Tang Dynasty poet Wang Bo's quatrains, is no longer exaggerated metaphor and emotional expression, but really can do. Not difficult to imagine, if there is no advanced developed global communications network, the people of the world's friendly exchanges and work, life will be how much inconvenience! The birth of communication network, known as the history of the development of a milestone in communications. Communication network was able to win this award, the most fundamental reason is because it conforms to the needs of modern social development. In the information is wealth, information is the victory of today's society, the value of time increased significantly, and sometimes early or late information to the moment, it will have a different effect. As communication and exchange of information communication, has never been as popular. People want communications to be fast, reliable, uninterrupted. In the "point to point" in the form of communication organization, if the transmission channel between the two is blocked, it will make the whole line can not be paralyzed communications, thereby delaying the transfer of information. In the establishment of the communication network conditions, the situation is quite different. Communication between the two direct routes, there are many circuitous circuit. When the communication network part of the circuit or equipment barriers, can automatically select the route, to achieve circuitous communication, this off each other, this resistance Pida, can be described as "the East does not shine bright, all roads lead to Rome." When the four communication nodes are connected to each other in a network, the total sum of the routes from the beginning of communication to the communication terminal is five, in other words, the communication can be established through five directions. When the five communication nodes When there are six communication nodes connected to each other, the number of routes from the beginning of communication to the communication terminal is increased to 65. As the number of routes, when a direction of information transmission congestion occurs, you can use the idle channel to replace, to achieve non-blocking transmission, thus greatly improving the timeliness of communication and communication, to maximize meet people's needs for communications. In the increasingly fierce electronic protest today, communication facilities often become the enemy's preferred target. How to improve the survivability of the survivability of communications to ensure uninterrupted flow of information, which is expected by the people. In this regard, the communication network can also be a show. When a large number of communication channels in accordance with a certain law woven into a network, the local network damage is only a certain impact on the communication call loss rate, so that the rate of decline, but still guarantee the survival of communication between users, will not affect the communication Of the overall. For example, when four communication nodes are connected to form a mesh network with six pairs of wires, if one of the pair of wires breaks down, the communication nodes can be kept in communication with each even in the case of three pairs of wires, To do this, thus greatly enhance the communication network survivability, so that uninterrupted transmission of information. Communication network with its excellent characteristics, occupies a very important position in the field of communication, a communication system in the nerve center. With the increasingly information-based society, whether military communications network or civil communication networks are constantly evolving, the emergence of many rookie. Here are the blooming in the network world, a few flowers long bright flowers, they are optical fiber communication network, microwave relay communication network and satellite communications network. The three communication networks from the ground to the air until nine days, the entire earth coverage, as the composition of the three pillars of modern communications networks.

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