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06 September 2012

data communication

The first time the computer was invented, he could not communicate with each other. At that time the computer is very simple. Thanks to technological advances in the field of electronics, computers began to grow rapidly and is increasingly perceived benefits in our lives. Today computers have mushroomed everywhere. The computer is not only monopolized by companies, universities Univeristy, or other institutions, but now the computer is able to be privately owned like we have a radio.The majority of computer users are at companies or offices. A large companies often have branch offices. When a company that has branches in some places is not efficient when performed whenever data processing should be sent to a central computer with the manual method. It should be noted that the functioning of a computer to generate information that is really reliable, so far as possible the data is entered completely original from the first-hand data recording and processing has not suffered from hand to hand.If so what about the data that will come from dioleh branches scattered in some places far away from the computer center. Here the importance of built a computerized system, primarily to reduce the time required for data processing. But the fact is, the circulation of a data processing system, the processing itself is only a part. Broadly speaking, a circulation system consisting of data processing of data collection, processing, and distribution. Of circulation problems encountered from companies precisely in terms of data collection and distribution of data and information for multiple locations.Understanding Data Communications closely related to the delivery of electronic transmission of data using a single terminal system computer to another computer terminal. The data referred to here is the electromagnetic signals generated by the source data that can be captured and sent to the receiving terminals. The definition of the terminal is a terminal equipment for data such as disk drives, printers, monitors, keyboards, scanners, plotters, and so forth.Why do we need a technique of data communication between computers one with another computer or terminal. One is as follows:

    
The existence of distributed processing, networking is absolutely necessary as a means of exchanging data.
    
Transactions often occurs at a different location to the location of the data processing or the location where the data will be used, so the data needs to be sent to the processing of data and sent it to the location that needs the information from the data.
    
Usually more efficient or cheaper to send data over communications lines, especially when the data has been organized through a computer, compared with the normal delivery.
    
An organization that has multiple locations data processing, data from a location that is busy processing can divide their duties by sending data to other processing locations that are less or not busy.
Computer networks began to develop in the early 1980s as a communication medium of communication is growing rapidly. So far the computer into a very effective means of communication and almost all forms of information involves the use of computers.With the invention of the internet, information can be accessed from home with little cost. Data communication is actually a combination of two techniques that is far different from the data processing and telecommunications. Can be interpreted that provides data communication services jarauk Juah communication with the computer system.
 
MODEL OF COMMUNICATIONIn the process of data communications from one location to another, there must be at least 3 main elements, namely the system data source, the transmission medium and receiver. If one element is missing, the communication can not be performed. Broadly speaking, the data communication process described below:Data Sources.Understanding data source is the element assigned to transmit information, for example a computer terminal, the data source is generating news or information and put it on the transmission medium. Sources are generally equipped with a transmitter that serves to transform the information into a form that will be mailed according to the transmission medium used, among other electrical pulses, electromagnetic waves, digital pulse. An example of the transmission is a modem device that served to awaken the PC as a digital bitstream from becoming sources of data that can be transmitted over analog telephone network toward the destination.Media TransmissionA data transmission medium in which the path data transmission process daari single source to a data receiver. Some of the data transmission medium that can be used or the transmission path of the data transmitted carrier, can be wires, electromagnetic waves, and others. In this case serves as a point of information to arrive at its destination.There are several issues related to the data transmission channel capacity and transmission type, transmission code, transmission mode, the protocols used and the use of transmission error.Some transmission media digunaka include: twisted pair, coaxial cable, fiber optics and electromagnetic waves.Recipient Data.Understanding the data receiver is a device that receives data or information, eg telephone, computer Terninal, and others. Functioning mnerima data sent by a source of information. Perima is suata tool called receiver function to receive signals from the transmission system and incorporate them into a specific shape can be captured and used by the recipient. For example, a modem that serves as a receiver that receives analog signals sent over telephone lines and turn it into a bit stream that can be captured by the recipient's computer.To facilitate understanding, communication can be explained with a simple model of communication, such as in Figure 4.2. Usability basis of this communication system is running the exchange of data between the 2 parties. In the figure given example, the communication between a workstation and a server which is connected with a bunch of a telephone network. Another example could be the exchange of voice signals between 2 phones on the same network.Here is an explanation of the sample data communications

    
Source (Source). This equipment generates data that can be transmitted. Suppose the phone and a PC (Personal Computer)
    
The transmitter (sender). Often the data generated from the source system is not transmitted directly in its original form. A transmission is quite moving and marking information in the same way as generating electromagnetic signals that can be transmitted over multiple sequential transmission system. For example, a modem job delivering a stream of digital bits from a device that had previously been prepared such as a PC, and menstransformasikan bit stream into an analog signal that can be transmitted over the telephone network.

    
Transmission System. The form of a single transmission line or a complex network that connects the source to the destination.
    
Receiver (Receiver). Receiver receives signals from the transmission system and incorporate them into a specific shape that can be captured by the objective. For example, a modem will receive an analog signal coming from the network or transmission line and turn it into a digital bit stream.
    
Destination (Destination). Capturing data generated okeh receiver.
FORMS OF COMMUNICATION DATAA data communications system may take the form offline communication system (communication system offline) or online communication system (online communication system). Data communication systems can be started with a simple system, such as terminal access network, the network that allows an operator to gain access to the facilities available in the network. Operators can access the computer in order to obtain, for example, run an application program, database access, and communicate with other operators. In an ideal environment, all of these facilities should seem as if the terminal, although they are physically located in separate locations.Off line communication systems.Offline communication system is a system for sending data over telecommunications facilities from one location to the central data processing, but the data is not sent directly processed by the CPU (Central Processing Unit). As in Figure 4.3, where the data to be processed is read by the terminal, then using a modem, the data is transmitted via telecommunications. At the point the data is received also by the modem, then the terminal, the data is saved to the address on the recorder such as a floppy disk, magnetic tape, and others. From this data recorders, will be processed by computer.Equipment needed in offline communication systems, among others:1. TerminalTerminal is an I / O device that is used to send data and receive data remotely using telecommunications facilities. This terminal equipment of all sorts, such as magnetic tape units, disk drives, paper tape, and others.2. Lines of communicationCommunication lines are often used telecommunications facilities, such as: telephone, telegraph, telex, and also with other facilities.3. ModemModel stands for Modulator / Demodulator. A device that transfers data from system digital code into analog coding system and vice versa.Online Communication System.In On line communication system, the data is transmitted via a computer terminal can be directly obtained, directly processed by the computer at the time we need.Online Communication System may include:

    
Realtime system
    
Batch Processing System
    
Time sharing system
    
Distributed data processing system
Realtime systemA realtime system makes it possible to transmit data to a central computer, computer central processing immediately upon the data received and later sent back to the sender of the data processing results immediately. American Airlines is a company that was first pioneered this system. With realtime system, passenger aircraft of a certain airport or agents can book tickets for a particular flight and get a result less than 15 seconds, just to see if there are seats on the plane or not.Realtime system also allows removal of the time required for data collection and data distribution. In this case, apply two-way communication, ie sending and receiving a response from the computer center in a relatively rapid.In realtime system, a high-speed data communications. Information needs should be met at the same time or within the spot. In this system the process is done in a matter of a few seconds, so that the required communication channels are fast, fast processing systems as well as memory and storage systems or very large buffer.Use of this system requires a technique in terms of system design, and programming, it is due to the need for a central computer data bank or database that is ready for any need. Usually the equipment is used as the database is a magnetic disk storage, because the process can be direct access (direct access), and please note that the system uses multiprogramming ability to serve a variety of purposes in the same time.Time sharing systemTime-sharing system is a technique use online system by several users in turn according to the time it takes users (Figure 4.5). CPU time due to the faster development of the processes, while the device Input / Output can not keep pace with the speed of the CPU, the speed of the CPU can be used efficiently by serving some of the tools I / O in turn. Christopher Strachy in 1959 has given an idea about the distribution of the time taken by the CPU. New in 1961, the first time the system is actually shaped time-sharing system conducted at MIT (Massachusetts Institute of Technology) and was named the CTSS (Compatible Time Sharing System), which could serve as many as eight users using the IBM 7090 computer.One use of time-sharing system can be seen in the use of a terminal at a bank teller. When a customer comes into the bank to save money or take out money, the savings book placed on the terminal. And by the terminal operator is recorded via the keyboard (the keyboard), then the data is sent directly to the central computer, process, calculate the amount of money as you want, and print them on the passbook for transactions has just done.Distributed data processing systemDistributed data processing (DDP) system is a form that is often used now as the development of time-sharing system. When multiple independent computer systems, each spread can process its own data, and associated with the telecommunications network, hence the term time-sharing is no longer appropriate. DDP system can be defined as an interactive computer systems that are geographically dispersed and connected by lines seitap telecommunications and computers capable of processing data independently and have the ability to relate to other computers in a system.Each location uses a computer that is smaller than the central computer and have savings outside of their own and can perform the data processing itself. Job is too big that can not be dioleh in itself, can be retrieved from a central computer.
  
DATA COMMUNICATIONS NETWORKData Communication Network or Computer Network is a group of computers that are connected to each other using certain protocols and transmission media. Based on the achieved coverage area computer networks can be classified into: Local Area Network (LAN) and Wide Area Network (WAN). LAN coverage area smaller than a WAN typically consists of a group of buildings that are close together.Topology NETWORKNetwork topology is a way to connect computers or terminals in a network. Model of the existing network topology include: Star, Loop, ring and bus.Star TopologyIn this topology cntral LAN consists of a node that serves as a regulator of the flow of information and personnel in Java communication in a network. So if one node wants to communicate with another node it must be through a central node. The function of the central node is very important here, usually in these systems must have high reliability.Bus TopologyOn this bus topology, each node is connected to another node with the data path or bus. All nodes have equal status with each other.Loop TopologyThis loop topology links between nodes are serialized in the form of a closed circle. All nodes have the same status.In the loop topology, every node can perform tasks for different operations. This topology has the disadvantage, if one node is damaged it will cause disruption DAPT communication between nodes to each other.Topology RingRing topology or ring topology is a topological result of a merger between the loop topology bus topology. The advantage is that if one node is damaged, it will not disrupt the communication between nodes because faulty nodes tersebtu placed separately from the data path.

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