Introduction to Data Communication/Transmission
Communication means an exchange of information between two or more parties and it can be exchange in a variety of way, that might be in the form of word, letters, messages drawing, body movement or any other symbols that represents the idea which make to other understandable. Data communication entails electronically exchanging data or information. It is the movement of computer information from one point to another by means of electrical or optical transmission system. This system often is called data communication networks.
Data Communication systems can therefore be defined as the combinations of facilities including software to aid data movement from one location to the other electronically:
In today's computing world, data refers to facts, statistics, pictures, voice and other information that is digitally coded and intelligible to variety of electronic machines. The key technology of the information age is computer communications. The value of high-speed data communication network is that it brings the message sender and receiver closer together in time. Data communication and networking is a truly global area of study. It facilitates more efficient use of computers and improves the day to day control of business by providing faster information flow. The information society where information and intelligence are the key drivers of personal, business, and national success has arrived. Data communication is the principle enabler of the rapid information exchange and will become more important than the use of computer themselves in the future. To be more familiar that what is data communication and its capabilities along with its limitation, we have to be familiar with the data communication media, components of data communication
Communication media
It is necessary to have a pathway or the media to transmit data from one point to another. The term media means the device that transmits the voice or the data form one point to another. Many different types of transmission media are in use today for example: copper wire, glass or plastic cables, which are called fiber optic cables or air transmission (radio, infrared, microwave, or satellite). There are two types of media; one is guided media and another is radiated.
In Guided media the messages flow through the physical media like twisted pair-wire, coaxial cable, fiber optic cables, the media guided is the signal.
In Radiated media messages is broadcast through the air such as infrared, microwave, or satellite.
Data Transmission and Communication Device
Data is the specific individual facts or the facts, from which decision can be made; it is the raw facts that can be processed into accurate and relevant information. Digital and analog is the two types of fundamental data; Digital and analog transmission have the following features;
· computers produce the digital data where as telephone produces analog data.
· Digital data are binary either on or off and the analog data is the sound wave.
· Analog signals are continuous waves that carry information by the characteristics of the waves. Analog transmission is the transmission of a continuously variable signal as opposed to a direct on/off signal.
· The traditional way of transmits telephone signal is an example of analog transmission. Digital signal is a discontinuous signal whose various states are discrete intervals apart, such as +15 volts and -15 volts. Most computers transmit the data in a digital form over the digital circuit to the attached device for example to the "printer" same as analog voice data also can transmit to the analog form through the telephone networks.
Data can be transmitted from one specific form to another. For example; as we know most of computer produces the digital data; we can convert digital data to analog voice data by using the special device called MODEM through the analog telephone circuit.
Data transmission may be either asynchronous or synchronous.
Asynchronous transmit only one character at a time and during transmission the character is preceded by a start bit and followed stop bit that lets the receiving device known where a character begins and ends. Asynchronous transmission is inherently inefficient due to the additional overhead required for start and stop bits, and the idle time between transmissions. It is therefore generally used for only low speed data transmission.
Synchronous transmission is a form of transmission in which data is sent as a block using frames or packets. In Synchronous transmission a group of character is sent to communication link in a continuous bit stream while data transfer is controlled by a timing signal initialed by the sending device. Used for high speed transmission.
ON-LINE DATA TRANSMISSION
This means that communication lines are directly connected to the computer either by means of a multiplexor or (Transmission controller) or by means of interface unit. The interface unit scans the communication lines frequently to dictate those that are ready to send or receive data. When a line is ready to transfer data, the scanning ceases and the channel number of the line is signalled to the CPU if the processor is in a position to accept data, then transmission begins.
OFF-LINE DATA COMMUNICATION
This type of data transmission indicates that the communication lines are not connected directly to the computer. Key-to-disk are often used for off-line preparation and transmission of data in remote job-entry-system.
ELEMENTS OF DATA COMMUNICATION
(a) Information Source
(b) Message
(c) Transmitter (d) Signal
(e) Receiver
(f) Information Destination
Information Source: Originator of messages wishing to convey information to another person.
Message: This is the idea/information that the sender wants to pass across to the receiver at a particular destination.
Transmitter: Wireless operator transmitting messages by means of a mouse key connected to transmitting set.
Signal: The signal produced by the transmitting set when the mouse key is depressed. Receiver: Wireless operator receiving message by means of a receiving set. Information Destination: Receipt of, message by addressee.
EQUIPMENT/COMPONENTS REQUIRED FOR DATA TRANSMISSION
(a) Multiplexor
(b) Front-End-Processor
(c) Concentrator
(d) Modem
Modems
MODEM Stands for MODulator DEModulator is used to convert analogue signal to digital and vice versa. A modem is a device that modulates and demodulates the signals. Modulation means the conversions of data from digital signal to analog signal and demodulates means the conversion of data signal from analog to digital signal. Modems are always use in pairs. The unit at the sending end converts the digital signal to analog signals for transmission through the analog circuit; at the receiving end, another modem converts analog to digital for the receiving computer. Modem transmission rate is measured in bits-per-second and it usually expresses bps. The amount of data actually transferred for one system to another is depends upon the speed of the modem.
Front-End Processor (FEP): A front-end processor is the special purpose device; this specialized computer manages all routing communications with peripheral devices. For large mainframe installations, a front-end processor is typically a special purpose minicomputer. The primary application of the FEP is to serve as the interface between the host/client computer and the data communication network with its thousands of terminals or microcomputers. It can handle coding and decoding data, error diction, retrieval of message, interpreting, and processing of the control information, addressing, routing message to the right computer, and breaking the long message in to small packets. Front-end processor can provide up to 30 percent additional processing time for mainframe.
Multiplexors
Multiplexors is an electronic device that allows a single communications channel to carry data transmissions simultaneously from many sources. Multiplexing a data communication means that two or more information is sent simultaneously via the communication circuit. Multiplexors is transparent, when the circuits are multiplexed at one end and demultiplexed at the other, each user's terminal or microcomputer thinks it has its own separate connection to the host computer. The objective of multiplexor is to reduce communication costs by allowing the more efficient use of circuits through sharing.
TYPES OF TRANSMISSION
Simplex Channel: In this type of communication, transmission takes place in one direction. The system known as Teletex, the sending of data alongside a television signal, is a good example of a simplex channel. Here the recipient has no formal means of communicating with the originator to ask for a repeat if there is an error Half-Duplex: This communications is bi-directional, but transmission moves in one direction at a time. The example is in radio telephone conversation. A protocol using the word "over" to allow the direction of data flow to change is used.
Full- Duplex: this allows bi-directional communication simultaneously. This is used for normal telephone conversation where both the initiator and the receiver can talk at the same time.
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