4th week: Data communication

here come how the data can communicate between user and computer.

ü definition of data communication

ü type of signal

ü data transmission mode

ü data flow

definition of data communication

Data communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel. The data are represented as an electromagnetic signal.

Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an Analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes.

type of signal

2 type of signal:

~ Analogue signal

Ø formed by continuously varying voltage level

Ø wave can be grasped by an analogue transmitter

Ø frequency is a completed wave’s cycles, measured in hertz(Hz)

Ø Hz is cycle per second

Ø Amplitude is the wave’s height, measured in Volt(V)/decibel(dB)

Ø Strong signal create higher amplitude

Ø Signal transmit via PSTN line (phone line)

~ Digital signal

Ø Transmission of binary electrical

Ø Is language of computer

Ø Represent of a square wave

data transmission mode

parallel communication is a method of sending several data signals simultaneously over several parallel channels. This distinction is one way of characterizing a communications link.

A parallel channel will generally have additional control signals such as a clock, to indicate that the data is valid, and possibly other signals for handshaking and directional control of data transmission.

                               

serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. Serial communication is used for all long-haul communication and most computer networks, where the cost of cable and synchronization difficulties make parallel communication impractical. 

there are 2 serial mode:

v Synchronous

o   Large group of data in blocks [frame]

v Asynchronous

o   Bit into small group

o   Transmit independently

data flow

 

Network devices use three transmission flow to exchange data, or "talk" to each other, as follows: simplex, half duplex, and full duplex.

• 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. 

   Simplex (One-Way Street)

  
• 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.
  
  

   Half Duplex (Center Turn Lane)

  
• 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.

  Full Duplex (Interstate Highway)

  

Full-duplex transmission is, in fact, two simplex connections: One connection has traffic flowing in only one direction; the other connection has traffic flowing in the opposite direction of the first connection.

multiplexing 

multiplexing (also known as muxing) is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium.

The aim is to share an expensive resource.

A device that performs the multiplexing is called a multiplexer (MUX).

In telecommunications, a multiplexer is a device that combines several input information signals into one output signal, which carries several communication channels, by means of some multiplex technique.

A demultiplexer is, in this context, a device taking a single input signal that carries many channels and separates those over multiple output signals.

enjoy some video about 

data communication

as usual, click on the icon below to the link 

By Mhui