Data communications are the exchange
Data communications are the exchange of data between two devices via someform of transmission medium such as a wire cable. For data communications tooccur the communicating devices must be part of a communication system madeup of a combination of hardware (physical equipment) and software (programs).The effectiveness of a data communications system depends on four fundamentalcharacteristics: delivery, accuracy, timeliness, and jitter.
1. Delivery. The system must deliver data to the correct destination. Data must bereceived by the intended device or user and only by that device or user.
2. Accuracy. The system must deliver the data accurately. Data that have beenaltered in transmission and left uncorrected are unusable.
3. Timeliness. The system must deliver data in a timely manner. Data deliveredlate are useless. In the case of video and audio, timely delivery meansdelivering data as they are produced, in the same order that they are produced,and without significant delay. This kind of delivery is called real-timetransmission.
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the unevendelay in the delivery of audio or video packets. For example, let us assume thatvideo packets are sent every 3D Ms. If some of the packets arrive with 3D-msdelay and others with 4D-ms delay, an uneven quality in the video is the result.
Representation of Data Communication
Information today comes in different forms such as text, numbers, images, audio, and video.
• Text
In data communications, text is represented as a bit pattern, a sequence of bits (0s
or 1s). Different sets of bit patterns have been designed to represent text symbols.
Each set is called a code, and the process of representing symbols is called coding.
• Numbers
Numbers are also represented by bit patterns.
Images are also represented by bit patterns. In its simplest form, an image is
Composed of a matrix of pixels (picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution. For example, an image can be divided into 1000 pixels or 10,000 pixels. In the second case, there is a better
representation of the image (better resolution), but more memory is needed to store the image.
• Audio
Audio refers to the recording or broadcasting of sound or music. Audio is by nature different from text, numbers, or images. It is continuous, not discrete. Even when we use a microphone to change voice or music to an electric signal, we create a continuous signal.
• Video
Video refers to the recording or broadcasting of a picture or movie. Video can either be produced as a continuous entity (e.g., by a TV camera), or it can be a
combination of images, each a discrete entity, arranged to convey the idea of motion.
Components of Data Communication
The data communication system consists of the following:-
(a) Transmitter or Sender of Data: - These may be terminals, computer and mainframes etc.
(b) Medium: - It is the medium though which the data is being transmitted. These as cabling, Radio Frequencies, microwave, fiber optics, infrared, wireless etc.
(c) Receiver:-As the name implies, it is the device which receives the transmitted data. These are printers, terminals, mainframes, computers, cell phones etc. The transmitter-medium interface and medium-receives interface have been, the transmitter may be a device which transmits a signal in such a format that is not Compatible with the medium. Similarly, medium may provide a signal in unacceptable format to the receiver. Hence, the signal from transmitter to medium and vice-versa requires conversion of signal from one form to another
Data Circuit Terminating Equipment: - It is also known as DCE is the equipment that interfaces the source and the medium and medium and source. DCE includes modems, DSUs and CSUs, and front End Processors. Each device is located at both ends of a communication circuit.
Data Terminals Equipment (DTE):- The equipment is a data communication system terminal that input data. In general, data terminals have a human machine interface. A typical example of DTE is an ATM at a bank. In other words, DTE is the computer transmitting and receiving equipment, including a wide variety of dumb terminals, intelligent terminals and in the form of host computer such as mainframes and minicomputers.
Communications Software: - In a wider sense we understand that a transmitter or sender may be a terminal with communication and application software which controls the terminal and processes data. There may be more than one terminal connected to the sender. Communications software is generally embedded in the computer operating system. Alternatively, it can take the form of a system task under the control of computer system.
A given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterized by:
1. Delivery. The system must deliver data to the correct destination. Data must bereceived by the intended device or user and only by that device or user.
2. Accuracy. The system must deliver the data accurately. Data that have beenaltered in transmission and left uncorrected are unusable.
3. Timeliness. The system must deliver data in a timely manner. Data deliveredlate are useless. In the case of video and audio, timely delivery meansdelivering data as they are produced, in the same order that they are produced,and without significant delay. This kind of delivery is called real-timetransmission.
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the unevendelay in the delivery of audio or video packets. For example, let us assume thatvideo packets are sent every 3D Ms. If some of the packets arrive with 3D-msdelay and others with 4D-ms delay, an uneven quality in the video is the result.
Representation of Data Communication
Information today comes in different forms such as text, numbers, images, audio, and video.
• Text
In data communications, text is represented as a bit pattern, a sequence of bits (0s
or 1s). Different sets of bit patterns have been designed to represent text symbols.
Each set is called a code, and the process of representing symbols is called coding.
• Numbers
Numbers are also represented by bit patterns.
Images are also represented by bit patterns. In its simplest form, an image is
Composed of a matrix of pixels (picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution. For example, an image can be divided into 1000 pixels or 10,000 pixels. In the second case, there is a better
representation of the image (better resolution), but more memory is needed to store the image.
• Audio
Audio refers to the recording or broadcasting of sound or music. Audio is by nature different from text, numbers, or images. It is continuous, not discrete. Even when we use a microphone to change voice or music to an electric signal, we create a continuous signal.
• Video
Video refers to the recording or broadcasting of a picture or movie. Video can either be produced as a continuous entity (e.g., by a TV camera), or it can be a
combination of images, each a discrete entity, arranged to convey the idea of motion.
Components of Data Communication
The data communication system consists of the following:-
(a) Transmitter or Sender of Data: - These may be terminals, computer and mainframes etc.
(b) Medium: - It is the medium though which the data is being transmitted. These as cabling, Radio Frequencies, microwave, fiber optics, infrared, wireless etc.
(c) Receiver:-As the name implies, it is the device which receives the transmitted data. These are printers, terminals, mainframes, computers, cell phones etc. The transmitter-medium interface and medium-receives interface have been, the transmitter may be a device which transmits a signal in such a format that is not Compatible with the medium. Similarly, medium may provide a signal in unacceptable format to the receiver. Hence, the signal from transmitter to medium and vice-versa requires conversion of signal from one form to another
Data Circuit Terminating Equipment: - It is also known as DCE is the equipment that interfaces the source and the medium and medium and source. DCE includes modems, DSUs and CSUs, and front End Processors. Each device is located at both ends of a communication circuit.
Data Terminals Equipment (DTE):- The equipment is a data communication system terminal that input data. In general, data terminals have a human machine interface. A typical example of DTE is an ATM at a bank. In other words, DTE is the computer transmitting and receiving equipment, including a wide variety of dumb terminals, intelligent terminals and in the form of host computer such as mainframes and minicomputers.
Communications Software: - In a wider sense we understand that a transmitter or sender may be a terminal with communication and application software which controls the terminal and processes data. There may be more than one terminal connected to the sender. Communications software is generally embedded in the computer operating system. Alternatively, it can take the form of a system task under the control of computer system.
Transmission modes
A given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterized by:
- the direction of the exchanges
- the transmission mode: the number of bits sent simultaneously
- synchronization between the transmitter and receiver
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