Data Communication

What is data ??

·         “raw data” that had been processed, arranged, stored

and will be used to get information

What is 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

Type of signal : 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 :

1.Frequency-

number of completed wave’s cycles. Measured in

Hertz (Hz), which is cycle per second

2.Amplitude-

wave’s height that measured in voltan(V) or decibel

(dB). A strong signal will create higher amplitude.

Type of signal : 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.

TRANSITION MODES

A given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterised by:

• the direction of the exchanges
• the transmission mode: the number of bits sent simultaneously
• synchronization between the transmitter and receiver

Simplex, half-duplex and full-duplex connections

There are 3 different transmission modes characterised according to the direction of the exchanges:

• A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...)
• A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.

• A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.  

 

SERIEL AND PARALLEL TRANSMISSION

The transmission mode refers to the number of elementary units of information (bits) that can be simultaneously translated by the communications channel. In fact, processors (and therefore computers in general) never process (in the case of recent processors) a single bit at a time; generally they are able to process several (most of the time it is 8: one byte), and for this reason the basic connections on a computer are parallel connections.

Parallel connection

Parallel connection means simultaneous transmission of N bits. These bits are sent simultaneously over N different channels (a channel being, for example, a wire, a cable or any other physical medium). The parallel connection on PC-type computers generally requires 10 wires. 

 

These channels may be:

• N physical lines: in which case each bit is sent on a physical line (which is why parallel cables are made up of several wires in a ribbon cable)
• one physical line divided into several sub-channels by dividing up the bandwidth. In this case, each bit is sent at a different frequency...

Since the conductive wires are close to each other in the ribbon cable, interference can occur (particularly at high speeds) and degrade the signal quality...

Serial connection

In a serial connection, the data are sent one bit at a time over the transmission channel. However, since most processors process data in parallel, the transmitter needs to transform incoming parallel data into serial data and the receiver needs to do the opposite. 

These operations are performed by a communications controller (normally a UART (Universal Asynchronous Receiver Transmitter) chip). The communications controller works in the following manner:

• The parallel-serial transformation is performed using a shift register. The shift register, working together with a clock, will shift the register (containing all of the data presented in parallel) by one position to the left, and then transmit the most significant bit (the leftmost one) and so on:

 

• The serial-parallel transformation is done in almost the same way using a shift register. The shift register shifts the register by one position to the left each time a bit is received, and then transmits the entire register in parallel when it is full: