DATA COMMUNICATION
TOPICS DISCUSSED IN THIS SECTION
- Components
- Data Representation
- Data Flow
The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.
The effectiveness of a data communications system depends on four fundamental characteristics:
DELIVERY:
The system must deliver data to the correct destination. Data must be-received by the intended device or user and only by that device or user.
ACCURACY:
The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.
TIMELINESS:
The system must deliver data in a timely manner. Data delivered late are useless.
In the case of video and audio, timely delivery means delivering data as they are produced.
JITTER:
Jitter refers to the variation in the packet arrival time.
COMPONENT
MESSAGE: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.
SENDER: The sender is the device that sends the data message, It can be a computer, workstation, telephone handset, video camera, and so on.
RECEIVER: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
TRANSMISSION MEDIUM: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission medium include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
PROTOCOL: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating.
DATA REPRESENTATION
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.
- 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.
- Today, the prevalent coding system is called Unicode.Other code is ASCII code developed some decades ago in the United States.
NUMBERS
- Numbers are also represented by bit patterns. However, a code such as ASCII is not used to represent numbers; the number is directly converted to a binary number to simplify mathematical operations.
IMAGES
- 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.
- After an image is divided into pixels, each pixel is assigned a bit pattern. The size and the value of the pattern depend on 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.
VIDEO
- Video refers to the recording or broadcasting of a picture or movie.
- Video can either be produced as a continuous entity or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion.
- Again we can change video to a digital or an analog signal,
DATA FLOW
Communication between two devices can be simplex, half-duplex, or full-duplex.
SIMPLEX:
In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive.
HALF-DUPLEX:
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.
FULL-DUPLEX (DUPLEX):
In full-duplex mode (also called duplex), bot stations can transmit and receive simultaneously.
