Chapter 3 Data communication

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/Sink Medium

Sender / Source Sender 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 Media A particular physical medium is used for data communication.

Radiated Media Communicating 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 Pair 2) 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 UTP STP 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.

Radiated Media (Unguided Media) 1. Radio transmission Radio transmission, which is very familiar to our normal lives, can be used for data communication very easily.

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

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

Communication satellites

Data Transmission Types Data 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 a computer 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 from sender 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 duplex Data can be transmitted both ways at a time. Example: Telephone. Both ways at a time

Duplex/Full duplex Router

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