Data communication

Chapter 3

Data communication

Prepared by: Anne Perera


What is data communication?

Transmission of data from one place to another place is called data communication.


Basic parts of data communication

Three components are essential in data communication.

1. Sender / Source

2. Data Communication Medium

3. Receiver / Sink


Basic parts of data communication

Sender/Source Receiver/SinkMedium


Sender / SourceSender or source is the data producer or the place where the data is produced for data transmission.E.g.: Imagine you call a friend of yours. Then you become the Sender or Source.

Sender


Data Communication Medium

The medium which is used to transmit data to the receiver.

E.g.: In the example mentioned above, telephone becomes the data communication medium there.


Receiver / Sink

The receiver is the person who gets data at the end.

E.g.: Your friend is the receiver in the above mentioned example.

Receiver


Data Communication Media/Medium

•Various media are used for data communication. •It is possible to divide all these media into two main types.

1) Guided Media 2)Radiated Media


Guided MediaA particular physical medium is used for data communication.


Radiated MediaCommunicating data using media which is not physical, is called radiated media.

Eg: Radio transmission, Infrared, Microwaves


Guided Media

Following wires can be classified under guided media.

•Twisted wire pair (Twisted pair cables)

•Co-axial Cable / Coaxial cables

•Fiber optic cables


Twisted wire pair

•The normal wires used for daily activities can also be used for data communication. •A twisted pair consists of two copper wires about 1 mm thick. •Pairs of insulated copper wires twisted around one another for the reduction of Electromagnetic Interference.


Types of twisted wire pair

1) Shielded Twisted Pair2) Unshielded Twisted Pair


Shielded Twisted Pair

A Shielded Twisted Pair (STP) has a fine wire mesh surrounding the wires to protect the transmission.


Unshielded Twisted Pair

•An Unshielded Twisted Pair (UTP) do not have a wire mesh. •Not suitable for long distance transmission.


Twisted wire pair

Advantage of STP over UTPSTP reduces the interference.

Disadvantages of STP It is more expensive than UTP.


Advantages of Twisted pair cable

•Can carry both analog and digital data.•Easy to implement and terminate.•It is the least expensive media of transmission for short distances.•If portion of a twisted pair cable is damaged it does not affect the entire network.


Disadvantages of Twisted pair cable

•Very poor security and is relatively easy to tap.•Thin in size, they are likely to break easily.


Applications of Twisted Pair Cables

•Telephone lines to carry voice and data channels.

•ADSL lines.

•Some Local area networks.

•ISDN (Integrated Services Digital Network).


What is ISDN?Multiple devices can be attached to the line, and used as needed.


Asymmetric digital subscriber line (ADSL)

•A type of digital subscriber line (DSL) technology.•A data communication technology that enables faster data transmission over copper telephone lines.


Co-axial Cable / Coaxial cable

It has a copper net woven around a copper wire.


Applications of Coaxial cables•Used in digital transmission•Used for analogue transmission•Used for TV antennas and Cable TV


Advantages of Coaxial cables

•Easy to install

•Not expensive

•Since it shielded, can span a higher distance at higher speed than twisted pair.

•Less data loss


Disadvantages of Coaxial cables

•Higher cost compared to twisted pair

•Cables easily get damaged


Fiber Optics•Avery popular guided media used today for data communication. •Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair. •They are arranged in bundles called optical cables and used to transmit light signals over long distances.


Fiber Optics


Applications of Fiber Optics•Military -They offer better performance and greater security for their signals. They're strong, and lightweight, and can also be used outdoors in harsh environments.•Radar systems•Telecommunications companies to transmit telephone signals•Internet communication•Cable television signals


Advantages of Fiber Optics

•Carry signals with much less energy loss than copper cables. •Much lighter and thinner than copper cables.•Difficult to tap information.•Supports for long distances.•Supports for very high speed network communications.


Disadvantages of Fiber Optics

•It's very expensive.•Difficult to splice two cables together


Radiated Media (Unguided Media)

•No physical medium is used here to send data.



1. Radio transmissionRadio transmission, which is very familiar to our normal lives, can be used for data communication very easily.



2. Infrared•It has a very low frequency.•These are largely used for data communication when wire- less keyboards, mouse and printers are used.



3. Microwaves•Used to communicate data to a long distance and short signals with contain higher frequency.

•Microwave links use very high frequency radio waves to transmit data through space.


Microwaves


Radiated Media (Unguided Media)4. Communication satellitesData can be communicated using satellites which are installed high in the sky.

Prepared by: Anne PereraCommunication satellites


Data Transmission TypesData transmission can be done in two

ways.

1.Serial data transmission

2. Parallel data transmission


Serial data transmission•Data is transmitted here, one after the other (one bit at a time, in a serial way).

•Such data transmission is done in bits in acomputer network.

•One wire is enough here for data transmission.


Serial data transmission


Parallel data transmission

•Several bits are transmitted at a time

•Several wires are used for this.

•In most of the instances, use of at least eight wires for this is the normal way.


Parallel data transmission


Data Transmission Speed

The speed of data transmission is measured in

Bits per second (bps)Kbps (kilobits per second)

Mbps (Megabits per second) Gbps (Gigabits per second).


Data Transmission Modes

Three main modes are

1.Simplex

2. Half-Duplex

3. Duplex


Simplex•Data is directed one way only. •There is no any space for data transmission to be directed the other way. Examples: Television transmission

Radio transmission. From your computer to the printer. From the mouse to your computer.

•Data transmission is always done here only fromsender to receiver.


Simplex-Examples

One way only


Simplex-Examples

One way only

Television transmission


Simplex-Examples

One way only

Radio transmission


Half-Duplex

Data can be directed one way at a time.

The data flows in one direction or the other, but not both at the same time.

Example: Walkie-talkie.

Where only one party can talk to the other at a time


Half Duplex -Examples

Walkie-talkie


Half Duplex -Examples

Walkie-talkie.


Duplex/Full duplexData can be transmitted both ways at a time.

Example: Telephone.

Both ways at a time


Duplex/Full duplex

Router


END

Data communication

Education