Data Communication and Computer Networks-Terms used in Data communication

Terms used in Data communication
A. Data Signal
Analog signal is one type of continuous time-varying signals, and these are classified into composite and simple signals. A simple type of analog signal is nothing but a sine wave, and that can’t be decomposed, whereas a composite type analog signal can be decomposed into numerous sine waves. An analog signal is not resistant toward the noise, therefore; it faces distortion as well as reduces the transmission quality. The analog signal value range cannot be fixed.

Digital signals -These signals are discrete or not continuous. A digital signal carries the data in the form of binary because it signifies in the bits. These signals can be decomposed into sine waves which are termed as harmonics. Digital signals are more resistant toward the noise; therefore, it barely faces some distortion.

Modulation and demodulation

Modulation is the process of encoding information in a transmitted signal, while demodulation is the process of extracting information from the transmitted signal. A device that performs both modulation and demodulation is called a modem — a name created combining the first letters of Modulator and Demodulator.

Multiplexing and Demultiplexing
Multiplexing is a technique used to combine and send the multiple data streams over a single medium. The process of combining the data streams is known as multiplexing and hardware used for multiplexing is known as a multiplexer.
Multiplexing is achieved using a device called Multiplexer (MUX) that combines n input lines to generate a single output line. Multiplexing follows many-to-one, i.e., n input lines and one output line. Demultiplexing is achieved using a device called Demultiplexer (DEMUX) available at the receiving end. DEMUX separates a signal into its component signals (one input and n outputs). Therefore, we can say that demultiplexing follows the one-to-many approach.

The ‘n’ input lines are transmitted through a multiplexer and multiplexer combines the signals to form a composite signal.
The composite signal is passed through a Demultiplexer and demultiplexer separates a signal to component signals and transfers them to their respective destinations.
Advantages of Multiplexing:
• More than one signal can be sent over a single medium.
• The bandwidth of a medium can be utilized effectively.
D. Transmitter
A set of equipment used to generate and transmit electromagnetic waves carrying messages or signals. The transmitter’s function is to convert the message signal into a form which is suitable for transmission over the communication channel or medium.

E. Receiver
A receiver is a hardware module or device used to receive signals of different kinds, depending on the context of the application. It may receive analog electromagnetic signals or waves, or digital signals through wired media. It is the device that receives and decodes signals and then conditions or transforms them into something that another machine or computer understands.
F. Bandwidth
Is defined as a range within a band of frequencies or wavelengths. Bandwidth is also the amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).
G. Base band Signal
Is an original transmission signal that has not be modulated, or has been demodulated to its original frequency? Most telecommunications protocols require baseband signals to be converted, or modulated, to a higher frequency so they can be transmitted over long distances.
H. Attenuation
Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances.
Attenuation occurs on computer networks because of:
• Range – over longer distances both wired and wireless transmissions gradually dissipate in strength
• Interference – radio interference or physical obstructions, such as walls, dampen communication signals on wireless networks
• Wire size – thinner wires suffer from more attenuation than thicker wires on wired networks Transmission Modes in Computer Networks
Transmission mode refers to the mechanism of transferring of data between two devices connected over a network. It is also called Communication Mode. These modes direct the direction of flow of information.
There are three types of transmission modes. They are:
i. Simplex Mode
ii. Half duplex Mode
iii. Full duplex Mode

Synchronous and Asynchronous
Synchronous Transmission
In synchronous transmission, data moves in a completely paired approach, in the form of chunks or frames. Synchronization between the source and target is required so that the source knows where the new byte begins, since there are no spaces included between the data. Synchronous transmission is effective, dependable, and often utilised for transmitting a large amount of data. It offers real-time communication between linked devices. An example of synchronous transmission would be the transfer of a large text file. Before the file is transmitted, it is first dissected into blocks of sentences. The blocks are then transferred over the communication link to the target location.
Because there are no beginning and end bits, the data transfer rate is quicker but there’s an increased possibility of errors occurring. Over time, the clocks will get out of sync, and the target device would have the incorrect time, so some bytes could become damaged on account of lost bits. To resolve this issue, it’s necessary to regularly re-synchronize the clocks, as well as to make use of check digits to ensure that the bytes are correctly received and translated.

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