A Communication is the process of transferring messages from one point to another. It is a very vital process in a network. When two networks are connected with each others they have to share data to each others so this process of communication system has three basic elements which are as follows -
1. A sender (source), which creates the message to be transmitted.
2. A medium, which carries the message,
3. A receiver (sink), which receives the message.
Data communication is the function of transmitting data from one point to another. In this case, the sender and receiver are normally machines, in particular, computer devices (computers, terminals, peripheral devices like printers, plotters, disks, etc), and the transmission medium may be telephone lines, microwave links, satellite links, etc. However, the messages that are transmitted are only in data form, but not in voice conversations form. Hence, the electronic systems, which transfer data from one point to another, are called data communication systems unlike computers, which process and communication systems transmit data from one point rearrange to another without any change.
Data Transmission Modes:
There are three ways, or modes of transmitting data from one point to another. These are simplex, half duplex and full duplex.
1.Simplex: If transmission is simplex, comm unication can take place in only one direction. Devices connected to such a circuit are either a send-only or a receive-only device.
2.Half Duplex: A half duplex system can transmit data in both directions, but only in one direction at a time. Hence, a half duplex line can alternately send and receive data. It requires two wires.
3.Full Duplex: Some applications require simultaneous transmission in both directions. In such cases, a full duplex system is used, which allows information to flow simultaneously in both directions on the transmission path. Use of a full duplex line improves efficiency, because the line turn-around time required in a half duplex arrangement is eliminated. It requires four wires.
Data Transmission Speed:
1. Narrowband: Narrowband or subvoice grade. channels range in speed from 45 to 300 band. They are used for handling low data volumes, and are adequate for low-speed devices. They are used mainly for telegraph lines and low speed terminals.
2.Voiceband: Voiceband channels handle moderate data volumes, and can transmit data at speeds up to 9600 band. They are so called because their major application is for ordinary telephone voice communication. They are also used for data transmission from slow I/O devices to CPU or vice-versa. Moreover, most remote terminals are connected to computers through voiceband channels.
3. Broadband: Broadband or wideband channels are used when large volumes of data are to be transmitted at high speed. These systems provide data transmission rates of 1 million baud or more. A company might use a broadband facility for high speed computer-to-computer communication, or for simultaneous transmission of data to several different devices.
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