Communication and Networks :
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 (teleis 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 30
ms. If some of the packets arrive with 30-ms delay and others with 40-ms delay,
an uneven quality in the video is the result.
Components :
A data
communications system has five components (see Figure 1.1).
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