Chapter 13: Data Communication

Chapter 13: Data Communication

Data Communication

It is the process in which sending data electronically over a long distance. It involves 3 basic elements,

Source: A source is a system or device or person that produces message for sending.

Destination: A system or device or person that receives message is called destination.

Communication medium: They are used to transmit message from source to destination.

Characteristics of DC

Correct Delivery: Data must reach only the specified person.

Accurate Delivery: Data must be received the same form it was send.

Timely Delivery: Data must reach to the destination at proper time.

Communication Media

          They are classified in to two guided media and unguided media.

Guided Media (Bounded)

·        Electromagnetic signals are transmitted along a closed physical path

·        Example: Twisted Pair Wire, Coaxial Cable, Fiber Optics

Unguided Media (Unbounded)

·        Electromagnetic signals are transmitted through air, vacuum or water

·        Example: Micro Wave, Satellite, Radio Waves

Guided Media (Bounded)

Twisted Pair Wire

·        It consists of two insulated copper wires, twisted together in a helical form (DNA model) typically used in telephone system.

·        It can use several kilometers without amplification.

·        For more distances repeaters are needed

·        Twisted pair cable has more than one twisted pair wires. They are

·        Unshielded Twisted pair cable(UTP)

·        Shielded Twisted pair cable(STP)

UTP Cable

·        A set of twisted pair wires in a single plastic encasement.

·        Commonly used in telephone system.

·        Low cost and easy to install.

·        Carry both data and voice.

STP Cable

·        A set of twisted pair wires wrapped in a foil shielding (Metal shield).

·        High cost and difficult to install than UTP.

·        Carry both data and voice.

·        Metal shield avoids cross talk.

Coaxial Cables (Coax)

·        It consists of a central copper wire, surrounded by an insulating material.

·        The insulator is encased by a cylindrical conductor, it is covered in a protective sheath

·        Used in long distance Telephone system, Cable TV Networks at higher speed.

Two types of Coax are there. They are

·        Base band Coax

·        Broad band Coax

Base band Coax

·        Transmit a single signal at a time at high speed.

·        Commonly used in digital transmission.

Broad band Coax

·        Transmit many simultaneous signals in different frequencies.

·        Commonly used in analog transmission

Fiber Optics

·        Similar to coaxial cable, at the center there is a glass core through which the light propagates.

·        A cladding is used to keep all the light in the core

·        To protect the cladding a outer plastic jacket is used

·        They are reliable for transmitting huge amount of digital data

·        at high speed without errors.

·        Adv.& Dis. adv:- High bandwidth, Noise resistance,  High signal carrying capacity. But High cost, maintenance is too expensive, Difficult to install and fragility,

CLADDING

PROTECTING SHEATH

THIN GLASS CORE

Unguided Media (Unbounded)

Microwaves

·        They are high frequency radio waves. They travel in free air in straight line. Can transmit data signals up to 40 miles with high band width.

·        To transmit signals parabolic antennas are used. For long distance communication repeaters are used. Repeater includes a transceiver. (Transmitter + Receiver)

·        Used in long distance telephone communication and cellular communication

Satellites

·        Used to transmit data from one continent to another continent with 3-30 GHZ frequency.

·        Satellites are placed in atmosphere and they revolve the earth at the same speed of earth. So they are called geostationary satellite.

·        Satellite control station sends the signals to satellites from earth and parabolic antennas retransmit it to the destination.

·        Transferring signals from earth to satellite is called Uplink and from satellite to earth is called Downlink.

Radio Waves

·        They propagate surface waves for long distance communication. They have different frequencies from 3KHz-300GHz

USAGES

·        Submarine, Long range navigation, AM radio,

·        International broadcasting, Military, Telegraph,

·        VHF television, Mobile phone, Radar, FM radio, Aircraft Communications etc.

Analog and Digital transmission

·        A signal which is represented with the use of discrete states is called digital signal.

·        A signal which is represented with the use of continuous states is called analog signal.

Analog transmission

·        Here data transmitted in a continuous wave form.

·        Eg Telephone System.

·        Its characteristics are Amplitude, frequency and phase.

Digital transmission

·        Here data transmitted in discrete wave form. i.e. ON and OFF electrical states.

·        E.g.: Computer transmission

·        It is faster and efficient than analog transmission.

Mode of Communication

It refers in which manner data is transmitted from source to destination. They are,

·        Simplex

·        Half Duplex

·        Full Duplex

·        Serial

·        Parallel

·        Asynchronous

·        Synchronous

Simplex Communication

Here data transmitted in only one direction. The device can either receive or send the data. Can’t do both. E.g. A keyboard can only send data to a computer, one way traffic

Sender

Receiver

Half Duplex Communication

Here data transmitted in both direction but only one direction at a time. The device can receive and send the data. E.g.: Citizens Band Radio, Walkie-talkie, Narrow bridge traffic.

Sender

Receiver

Full Duplex Communication

Here data transmitted in both directions at same time. The device can receive and send the data. It is faster than other mode of communications. Eg: Telephone communication, two-way Traffic

Sender

Receiver

Serial Communication

Here data transmitted one after another in a serial manner. Here bits are sending one after another. Same cable is used for this. Used in long distance data communication. Bit by bit transmission are takes place here.

01010110

Parallel Communication

Here data transmitted by using multiple wires. Here a byte can send at a time. Each cable carry one bit. It is a fastest way to transmit data. But we have a number of wires in parallel.

0 1 1 0 1 1

Asynchronous Communication

Here data are sending with a checking bit. In this method one character is transmitted at a time. Character transfer is controlled by start bit and stop bits. It is slow and least expensive transmission.

Asynchronous Communication

Here data are sending with a checking bit. In this method one character is transmitted at a time. Character transfer is controlled by start bit and stop bits. Slow and least expensive transmission is this.

Synchronous Communication

Here block of data are send with a control characters. In this method a block of character is transmitted at a time. Character transfer is preceded and followed by control characters. Fast and expensive transmission is this. Used in computer networks.

Asynchronous V/S Synchronous

Asynchronous Ø One character is transmitted at a time. Ø Each bit surrounded by start and stop bit. Ø Low speed. Ø Least expensive Ø Timing error is high.

Synchronous Ø Block of characters is transmitted at a time. Ø Each block surrounded by control characters. Ø High speed. Ø High expensive Ø Timing error is low.

Characteristics of Signals

·        Amplitude

·        Period

·        Frequency

·        Phase

·        Wave length

Amplitude

The time ‘T’ taken to reach the signal back to its original starting position (Cycle) is called period

Frequency

The number of periods a signal complete in one second is called frequency. It measured in Hz Frequency=1/Period

Phase

Phase of a signal is related to the position of a wave from relative to time zero. It is measured in Degree or Radian.

Wave length

The distance between two maximum and two minimum is called wave length

Data Communication Devices

·        Modem

·        Repeater/Hub

·        Router

·        Bridge

·        Gateway

·        Multiplexer

·        Concentrator

Modem

A modem is a device that is used to convert analog signals to Digital Signal and vice versa.

Modulation:-Conversion from digital to analog

Demodulation:-Conversion from analog to Digital

Modem is used when we gathering information from internet. Because the data transfer media here is telephone line. Telephone line carries only Analog signals and computers works with digital signal.

Repeater or Hub

This device is used for receiving, amplifying and transmitting signals in both directions. It amplifies the weak signals. So they are used in long distance transmission. It is used especially in LAN.

Router

The process of determining how a connection is to be setup is called routing. Router chooses an efficient path for data transfer from a group of paths. Also a router joints two networks with different protocols.

Bridge

The device that is used to connect similar LAN is called bridge. Here can establish security for data to avoid unauthenticated using.

Gateway

It is used to connect the dissimilar networks is called Gateway. Many networks exist in world with different hardware and software. To inter connect these networks we use the device Gateway.

Multiplexer

Multiplexing is the process in which it combines more than one signals in to one signal. The device used for this called multiplexer. Multiplexer combines the input from different sources and loads them on a single channel of a medium, its reverse process is called De-multiplexing.

Concentrator

If a number of devices connecting to a computer the data from these devices cannot access simultaneously. The concentrator store (Buffer) these data according its priority and serve it in to the computer.

Concept of Protocol

Communication Protocols are set of rules and standards that allow different devices to allow effective communication.

Commonly Used Protocols

•         IP (Internet Protocol)

•         TCP (Transmission Control Protocol)

•         FTP (File Transfer Protocol)

•         SMTP (Simple Mail Transfer Protocol)

•         HTTP (Hyper Text Transfer Protocol)

•         POP (Post Office Protocol)

Internet Protocol (IP)

•         It is a protocol used by the internet for transferring message from one system to another.

•         The messages are send in the form of packets.

•         IP supports routing and relaying.

•         It use in packet format of TCP/IP reference model

•         IP address is number combination of network number and host number to identify the host computer.

•         E.g. 164.120.9.61

Transmission Control Protocol

•         It ensures the reliable delivery of data between hosts.

•         It collects the packets in proper order.

•         It use in transport layer of TCP/IP reference model

File transfer protocol (FTP)

•         Used for transferring files in computer networks.

•         It use in application layer of TCP/IP reference model

•         It is easier protocol.

•         Most useful way to sharing information.

Simple Mail Transfer Protocol (SMTP)

•         Helps to send and receive mail between networks.

•         Here a user can specify the destination address and message.

Hypertext Transfer Protocol (HTTP)

•         Used to transfer hypertext documents and data from one computer to another.

•         This protocol used to communicate web server and web client computers.

Post Office Protocol (POP)

•         It includes command for login, logout, view message and delete message from a remote mail box.

•         It accepts email from a remote computer and store in personal computer for further usage.

Access Methods

•         It concerned with the channel selection.

•         It controls the use of single channel for different users at a time.

They are

§  CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

§  Token Passing

CSMA/CD

•         A protocol in which node listens for a transmission and act accordingly are called carrier sense protocol.

•         In CSMA/CD transmission occurs when the nodes detect the channel is idle.

•         When a node detects a collision then stop the transmission.

•         It is used in LAN

Token Passing

•         Simplest method to access a channel.

•         Here use a special bit called Token

•         The node that holds the token can send the data.

•         Only one node can send data at a time

•         No collision occurs.

Internet Terminologies

The net works of net work is called internet. Vinton Cerf is known as the father of internet. Here TCP/IP reference model is used for communication. The International Network is more commonly known as the Internet. The Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections, etc.

          The requirements for an Internet connection are Computer, Modem, Telephone line, Internet account, Browser soft ware’s etc.

www (World Wide Web)

It is a huge, online storage of information that can be provided to users. It is also a service operated by the internet to access any document on the network without login. This service is based on client –server based model.

Website

          Website is a collection of web pages like a brochure (collection of digital pages) that are stored digitally on the web server. Web server means the computer in which the web sites are stored. The process of storing website in a web server is called website hosting. Each web page has a file name.

URL (Uniform Resource Locator)

          When wants to view the web site of a particular organization or a company the address of the web site should provided in the address bar of browser software (Soft ware’s used to display the web pages. Eg. Internet Explorer, Mozilla, Opera, Netscape navigator etc). The address of a website is called URL. After giving the proper URL we can see the home page of the organization.

http://www.bsnl.co.in is an example of an URL

Here ‘http’ is the scheme, ‘www’ is the host, ‘bsnl’ is the domain name, ‘co’ is type of firm and ‘in’ is the geographical region. (co, com, org, gov, edu are types firms and in, au, uk, ae are regions.).

Web page

          A web page is a simple text file that contains not only text but also a set of HTML tags that describes how the text should be formatted when a browser displays it on the screen. A web page contains text, pictures, graphics, animations, sounds etc. also it includes hyperlinks to other web pages or other documents. The file extension of web page is .htm or .html.

HTML (Hyper Text Markup Language)

HTML is a programming language for formatting the contents that are to be displayed as in a web page. The main feature of the HTML is to establish links (Hyper link) between documents. Hyper link is a visual element which can select by clicking mouse button and loads by searching other documents from a storage device. So HTML is used to publishing web pages on internet and used for creating on line help files.