Data Communication

DATA?
- “raw data” that had been processed, arranged, stored and will be used to get information

Data communication?
- Process of change / transfer information in a form of a digital data (binary) in between two or more devices using electronic delivery system.
- Data communication is transmitted via mediums such as wires, coaxial cables, fiber optics, or radiated electromagnetic waves such as broadcast radio, infrared light, microwaves, and satellites.

Type of signal
•Data comes in variety styles : text, voice, picture and video
•All this type of information needs to be converted into signal that can be understood by the      communication media in order to transmit the data from one place to another location.
•Data comes in two type of formation

1.Analogue signal
2.Digital signal

1. Analogue
•Is like the human voice
•Formed by continuously varying voltage level that create wave than be grasped by an analogue transmitter like microphone.
•Typically presented by their characteristics sine wave
•Analogue signal is transmit through PSTN line such as phone line
•Involves 2 parameters ;

Frequency : number of completed wave’s cycles. Measured in Hertz (Hz), which is cycle per second
Amplitude : wave’s height that measured in voltan(V) or decibel (dB). A strong signal will create higher amplitude.



2. Digital
-Transmission of binary electrical or light pulses that only have two possible states, 0 and 1 (language of computers)
-Digital format is ideal for electronic communication as the string of 1s and 0s can be transmitted by a series of "on/off" signals represented by pulses of electricity or light
-Presented as a square wave

-Digital signal need to be change into analogue signal to be transmitted through PSTN lines.

-The process of changing ;
1. Analogue to digital signal : modulation
2. Digital to analogue signal : demodulation
-Modem is the hardware that used to do this changing process

Data transmission mode

-Data need to be digitized before it can be transmitted through the electrical transmission medium.
-When we enter data into a computer via keyboard (alphabet or numeric), the data is encoded into an equivalent binary coded using standard coding scheme such as;
 1. Extended Binary Coded Decimal Interchange Code (EBCDIC)

 2. American Standards Committee for Information Interchange (ASCII)

-The digitized data are then transmitted through

1. Parallel transmission
- data is sent at least one byte at a time, each bit in the byte taking separate path
- means that a group of bits is transmitted simultaneously by using separate line for each bit

2. Serial transmission
- data sent one bit at a time, one after another a long a single path
-A bit slower compared to parallel transmission,
-used for short communication e.g between computer to printer

3 Seriel Transmission Modes

1. Synchronous Transmission
•data transmitted into blocks called “framed” or groups and transferred at regular specified interval
•Both sending device and receiving device are operated simultaneously and are resynchronized after each few thousand data signals bits are transmitted
•Only the start and end of the entire frame is mark with the start and stop bit
•This type of transmission mode are more efficient as fewer control bits involves

2. Asynchronous Transmission
•Used when the bits are divided into small group (bytes) and sent independently.
•The group of bits can be sent at any time and the receiver never knows when they will arrive (e.g: keyboard)
•Usually required a “start bit” to alert the receiver of incoming data and a “stop bit” to indicate the
end of transmission.

3. Isochronous Transmission
•data is sent at the same time as other related data to support certain types of real time applications e.g streaming voice, video and music


Directions/ Flow of Data Transmission

1. Simplex
•One way communications / one direction
•Role of transmitter and receiver are fixed

•Ex: radio station – transmits the signal to its listeners and listener never allows transmitting back

2. Half Duplex
•Flow in 2 direction but never at the same time
•One station transmits information to another station without any interruption
•The other station will response after that transmission has been completed
•Ex: Walkie-talkie

3. Full Duplex
•Data can moves in both directions at the same time
•Both station can transmit and receive simultaneously
•Consists of two simple channels; 1 channel used to forward while another as the reverse channel, linking at the same point
•Ex: Telephone
•Many networks and most internet connections are full duplex

Data Compression







Example of file compression formats, such as ARC and ZIP.