Data transmission uses the data processed for forwarding the same to the end-user. Data transmission, however, may simply involve forwarding of the data to the end- user. Whatever the case may be, data transmission could not be effected without using the means provided by the advances in the telecommunication field/ technology. Data communication, which consists of data processing as well as data transmission, generally requires the following:
1. Transmitter (source of information)
2. Converter at transmitting end
3. Transmission channel/carrier
4. Converter at the receiving end
5. Receiver (of transmitted information)
The data is transmitted using the telecommunication systems. The data is transmitted in the form of electromagnetic signals. These signals can be of two types: 1. Analog signal: It is a continuous waveform that passes through the communication medium. Analog signals are, rather were, used mainly to transmit data in the form of voice and to reflect variations in the pitch, across the line. The analog signal is in the form of waves of different frequencies and subject to distortion.
The waveform has three characteristics:
1. Amplitude (strength of signal)
2. Phase (direction of “flow” of the signal in a cycle time)
3. Frequency (number of times the waveform is repeated during a specified interval)
2. Digital signal: It is a discrete waveform that transmits data coded into two discrete states as !bits and 0 bits, which are represented as on-off electrical pulses. Digital signally is very useful in data communications. Now we are, indeed, moving into the “Digital Era” using the digital signal. Digital signal is generated by the microprocessor-based or controlled device. The digital signal has identical strength from source to destination. It is clear, rapid and distortion-free (less prone to noise distortion).
Digital Signal Modem: Modem is an abbreviation of MOdulation/DEModulation. A modem is a device that performs the translation from analog to digital or from digital to analog form of signal.
Communication channels and Transmission channels
Communication channels are the links/means by which data is transmitted from one device in a network to another. A channel can make use of various media like:
1. Physical connection lines
i. Twisted pair of copper wires
ii. Coaxial cables
iii. Optical fibre
2. Microwave lines
i. “Line of sight” earth microwave (tower to tower)
ii. Radio/wireless transmission waves (AM/FM)
Characteristics of communication channels
The communication channels mentioned earlier, have the following characteristics:
1. Transmission speed: It is the total amount of information that can be transmitted through any telecommunication channel and is measured in Bits Per Second (BPS). This speed is sometimes also referred to as “baud rate.”
2. Bandwidth: It is the capacity of the communications channel as measured by the difference between the highest and the lowest frequencies that can be transmitted by that channel.
3. Transmission modes: Transmission could be effected in different modes, viz., asynchronous transmission and synchronous transmission. In asynchronous transmission, one character is transmitted at a time and is used for low-speed transmission. In synchronous transmission, a group of characters is transmitted simultaneously. It is used for high-speed transmission of the block of characters.
4. Transmission direction: The data can be transmitted in the different direction using simplex, half-duplex or full-duplex transmission. While in simplex transmission, data can travel only in one direction at all times, in half-duplex transmission, data can travel/flow both ways, although it can travel in only one direction at a time. In full-duplex transmission, data can be directed/sent in either direction, simultaneously.
5. Communication processors: Data transmission and reception in a telecommunication network requires various processors. Some of them are mentioned below.
i. Front-end processors: It is a small computer dedicated to communication management and attached to the main/ host computer. It performs special processing activities like formatting, editing, routing, etc. related to communication.
ii. Concentrator: It is a programmable computer which collects messages from terminals and stores them till a bunch of messages — an economic size — is available. These messages are then sent together (“burst”) to the host computer.
iii. Controller: It is a specialized computer which supervises communication traffic between the CPU and peripheral devices.
iv. Multiplexer: It is a device, which enables a single communication channel to carry data transmissions from multiple sources, simultaneously.
v. Telecommunication software: The software resides in the host computer, front-end processor and other processors of a network. The special software is required to control and support the activities of the telecommunication network. Network control, access control, transmission control, error detection/correction, and security are some of the major functions of the telecommunication software.