Data Communications

DEFINITION

Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. data, text, voice, still picture, graphics and video is a example of information.

TYPES OF SIGNAL
Data comes in two forms:
digital signal

• transmission of binary electrical or light pulses
• have two possible states, 0 and 1
• represented as square wave
• need to be changed into analogue signal to be transmitted through PSTN
• PSTN (Public Switched Telephone Network) act as the media transmission
• modulation is a name of process of changing analogue to digital signal and demodulation is a process of changing digital to analogue.
• the hardware is used to do this process is a MoDem

 analogue signal

• formed by continuously varying voltage levels
• typically represented by their characteristic sine wave
• involves 2 parameters,which are frequency (the number of completed wave's circles) and amplitude (the height of wave).

             

BINARY DIGITS

Binary digit are basic or smallest units of measurement in digital that only consist the value of either 0 or 1. A byte is equal to 8 bit.

                                             

Understanding the Basics of Binary

 

Data Transmission Mode

Parallel transmission

• a group of bits is transmitted simultaneously by using a separate line of each bit. 

Serial transmission

• transmits all the bits one after another on a single line
• slower than parallel transmission
• best suit data communication needs to transmit data in a long distance
• there are 2 serial transmission modes which are synchronous and asynchronous transmission

 a) synchronous transmission

•  frame is a large group of data is transmitted in block
• In this method, both the sending device and the recieve device are operated simultanously and resynchronised
• it is occur after each few thousand data signal bits are transmitted

b) asynchronous transmission

• it is used when the bits are devided into small group (bytes) and sent independently
• the groups of bits can be sent at any time but the reciever never knows when they will arrive

Data Flow

1) Simplex transmission is like a one-way street where traffic moves in only one direction. Simplex mode is a one-way-only transmission, which means that data can flow only in one direction from the sending device to the receiving device.

example of simplex(television)

 2) Half-duplex transmission is like the center lane on some three-lane roads. It is a single lane in which traffic can move in one direction or the other, but not in both directions at the same time. Half-duplex mode limits data transmission because each device must take turns using the line. Therefore, data can flow from A to B and from B to A, but not at the same time.

example of Half Duplex(walkie talkie)

3)  Full-duplex transmission is like a major highway with two lanes of traffic, each lane accommodating traffic going in opposite directions. Full-duplex mode accommodates two-way simultaneous transmission, which means that both sides can send and receive at the same time. In full-duplex mode, data can flow from A to B and B to A at the same time.

example of Full Duplex( telephone)