DATA
COMMUNICATIONS BASIC LEVEL
When we communicate, we are sharing
information. This sharing can be local or remote. Between individuals, local
communication usually occurs face to face, while remote communication takes
place over distance. The term telecommunication,
which includes telephony, telegraphy, and television, means
communication at a distance (tele is
Greek for "far").
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. For data communications to occur, the
communicating devices must be part of a communication system made up of a
combination of hardware (physical equipment) and software (programs). The
effectiveness of a data communications system depends on four fundamental
characteristics: delivery, accuracy, timeliness, and jitter.
1.
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.
2.
Accuracy.
The system must deliver the data accurately. Data that have been altered in
transmission and left uncorrected are unusable.
3.
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, in the same order that they are produced, and without
significant delay. This kind of delivery is called real-time transmission.
4.
Jitter.
Jitter refers to the variation in the packet arrival time. It is the uneven
delay in the delivery of audio or video packets. For example, let us assume
that video packets are sent every 3D ms. If some of the packets arrive with
3D-ms delay and others with 4D-ms delay, an uneven quality in the video is the
result.
Components
of Data Communication
1.
Message.
The message is the information (data) to be communicated. Popular forms of
information include text, numbers, pictures, audio, and video.
2.
Sender. The sender is the device that sends
the data message. It can be a computer, workstation, telephone handset, video
camera, and so on.
3.
Receiver. The receiver is the device that
receives the message. It can be a computer, workstation, telephone handset,
television, and so on.
4.
Transmission
medium. The transmission medium is the physical path by which a message travels
from sender to receiver. Some examples of transmission media include
twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
5. 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, just as a person speaking French cannot
be understood by a person who speaks only Japanese.
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