Data Communication System: In the era of ICT we need to communicate with the outer world. In order to communicate, we have to share data and information. Data is transmitted on Internet in digital or analog form. But noise and attenuation can affect this. Noise is the external disturbances whereas attenuation is the degeneration of the signal.
As you can see in above image:
- Source: The message to be communicated is produced by the source. It can send it in any form be it a binary digit or a waveform, etc.
- An Encoder: Encoder represents any processing of the source messages/signals prior to transmission.
- The Channel: It is a medium, which is used for data transfer. A radio link, telephone line or a storage medium can be a medium. There may be different kind of disturbances on a medium. For example, in a telephone line the noise disturbance may be:
• Time varying frequency,
• Thermal noise,
• Impulsive switching noise, etc.
These disturbances may be corrected by an error correcting code.
The Decoder: A decoder decodes the data encoded by encoder to travel through the medium.
- The Destination: It is the receiver of the message. A person or object can be a receiver.
Some standard data transmission concepts are:
- The data may be transmitted as analog or digital form.
- It can travel through a single path serially or use number of parallel paths.
- The data can be sent asynchronously or synchronously.
Modes of Data Transmission are:
Simplex Mode: Only from one point to another point. It is unidirectional. The sender will send and receiver will receive, he cannot send back the data. Example: television telecast in non-interactive mode.
Half Duplex Mode: From one point to another and reverse but only one at a time. Data can flow from both the points but one at a time. Example : Walkie talkie.
Full Duplex Mode: Both ways simultaneously. The sender and receiver both can send and receive data. Signals going in either direction share the capacity. Sending and receiving data use half bandwidth each. Example: telephone communication.