Introduction to Data Communication:What are the fundamental characteristics of data communication? Data Flow :

Introduction to Data Communication:

When we communicate :we are sharing information. This sharing can be local or remote.

• - local communication usually occurs face to face .
• - remote communication takes place over distance.

What is data ?
refers to information presented in whatever form is agreed upon by the parties creating and using the data.

What is data ?
What are Data communications :
are the exchange of data between two devices via some form of transmission medium such as a wire cable.

NOTE:
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:

What are the fundamental characteristics of data communication?

1__Delivery:

What is 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:
What is accuracy ?
The system must deliver the data accurately.
Data that have been altered in transmission and left uncorrected are unusable.

3__Timeliness:
What is 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:
What is 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. 

What are components of data communication ?
A data communications system has five components :

 1__Message:
What is Message ?
The message is the information (data) to be communicated.
 Popular forms of information include text, numbers, pictures, audio, and video.

2__Sender:
What is 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:
What is 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:
What is Transmission medium ?
The transmission medium is the physical path by which a message travels from sender to receiver.

 Some examples of transmission media include :
What are transmission media :
 twisted-pair wire
 coaxial cable
 fiber-optic cable
and radio waves.

5__Protocol :
What is 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 Flow :

 

Simplex, Half Duplex, Full Duplex

What are the types of data flow?

Communication between two devices can be simplex, half-duplex, or full-duplex.

What is simplex communication?

1__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 .
• The simplex mode can use the entire capacity of the channel to send data in one direction.

What is Half-Duplex communication?

2__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.

NOTE

• In a half-duplex transmission ,the entire capacity of a channel is taken over by whichever of the two devices is transmitting at the time.
• The half-duplex mode is used in cases where there is no need for communication in both directions at the same time; the entire capacity of the channel can be utilized for each direction.

What is Full-Duplex communication?

3__Full-Duplex :
In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously.
NOTE

• The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time.
•  In full-duplex mode, signals going in one direction share the capacity of the link with signals going in the other direction.
• This sharing can occur in two ways:
• Either the link must contain two physically separate transmission paths :

one for sending and the other for receiving.
or the capacity of the channel is divided between signals traveling in both directions.

• One common example of full-duplex communication is
•  the telephone network.
• When two people are communicating by a telephone line, both can talk and listen at the  same time.
• The full-duplex mode is used when communication in both directions is required all the time.
• The capacity of the channel, however, must be divided between the two direction

What is data representation?

Data Representation : 

How is data represented in the computer?

Information today comes in different forms such as text, numbers, images, audio, and video. 

What is a type in data structure?
1__Text :

How do you represent text on a keyboard?

• 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.
• Today, the prevalent coding system is called Unicode, which uses 32 bits to represent a symbol or character used in any language in the world.
•  The American Standard Code for Information Interchange (ASCII) ,developed some decades ago in the United States,
•  now constitutes the first 127 characters in Unicode and is also referred to as Basic Latin.

What is Code ?
What is Coding ?
What is Uncode ?
What is American Standard Code for Information Interchange (ASCII) ?
What is Basic Latin ?

2__Numbers :

How do you represent 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.

2__Images: 

How do you represent 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.

NOTE:

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.
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.

3__Audio :

How do you represent 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.

4__Video :

How do you represent 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.

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