Introduction - Basics (Data Communication)

What does 'Computer Network' mean?  

Computer Network is a collection of devices (nodes) connected by a communication link. These devices that form a network (nodes) are capable of sending or/and receiving data.

They aid in Data Communication.

What is Data Communication? 

Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable/radio signals.

Here data refers to information in whatever form present. For example : while sending text messages, text is the data; while sending images, images are the data.

Various types of Data representation

Text

Numbers

Iamges

Audio 

Video

//pretty self explainatory. For more info regarding their respective properties (refer textbook pg5)

What are the criteria that must be considered to judge the effectiveness of data communication? 

1. Delivery 

- the data send must be recieved by the designated reciever(s).

2. Accuracy

- the data recieved must be the same as the data sent.

3. Timeliness

- delivery of data must happen in a timely manner. Delay in delivery might cause the data to be useless.

4. Jitter

- jitter refers to the variation in the packet arrival time. Sometime, while streaming a video, when the audio and the video packetes dont arrive in a timely fashion, it can lead to jitter.

What are the components that form a data communication system?

1. Sender   : the data is sent from.
2. Receiver : the data is intended for.
3. Protocol  : rules used to govern the transer of data.
4. Medium  : physical media by which the message is transferred
5. Message : the data (information) being communicated. 

Modes of Data Communication :

Modes of data communication can also be called as : Data Flow methods

1. Simplex

- Communication is uni-directional, like an one-way street. That is only one device always acts as the transmitter whereas the other device is always the reciever. 

Example : fm radio, we can only hear what they broadcast. We cannot talk back via the same devicem using the same medium. Similarly, televison as well.

2. Half Duplex

- Communiaction is bi-directional, but uni-directional at each instance.That is the transmission can happen two ways. But a device can be a transmitter or an reciver at an instance. 

Example : walkie - talkie, both parties with the walkie talkie can send as well as recieve. But at an instance, you can either talk or listen, one cannot do both.

If both parties try to communicate at the same time, the data collides and results in info lost.

3. Duplex

Communcation is bi-directional. Each device can act as both sender and reciever at the same instance of time as well.

Example : telephone calls, we can both talk and listen at the same time.