19 Data Communications and Networking Systems

Dr. Reni Francis

18.1 Introduction

18.2 Meaning of Data communication

18.3 Components of communication

18.4 Communication technologies

18.5 Communication technologies applications

18.6 Communication devices

18.7 Communication channels

18.8 Communication network types

18.9 Let us sum up

Learning Outcomes:

By the end of the lesson, students should be able to:

To understand the meaning of Data communication.
To be aware of the various components of Data Communications.
To understand the transmission of data on the basis of communication technologies
To understand the transmission of data on the basis of communication technologies applications
To understand the transmission of data on the basis of communication devices
To understand the transmission of data on the basis of communication channels
To understand the transmission of data on the basis of communication network types

18.1 Introduction:

This chapter provides an introduction to Computer networks and covers fundamental topics like data, information to the definition of communication and computer networks. The main objective of data communication and networking is to enable perfect exchange of data between any two points in the world. This exchange of data takes place over a computer network.

18.2 Meaning of Data Communication

When we communicate, we are sharing information. This sharing can be local or remote. Between individuals, local communication usually covers face to face, while remote communication take place over a distance. Data communication is the exchange of Data between two devices via some form of transmission medium. Data communication is considered local if the communicating devices are in the same building or a similarly restricted geographical area and is considered remote if the devices are farther apart.

For data communication to occur, the communicating devices must be part of a communication system made up of a combination of hardware and software. The effectiveness of a data communication system depends on three fundamental characteristics;

Delivery: The system must delivery data to the correct destination. Data must be received by the intended device or user and only by that device or user.
Accuracy: The system must delivery data accurately. Data that have been altered and left uncorrected are unusable.
Timeliness: The system must deliver data in timely manner. Data delivered late are useless. In the case of audio, video and voice data, timely delivery means delivering data that are produced in the same order that they are produced and without significant delay.

18.3 Components of Data communication

A Data Communication system has five components as shown in the diagram below:

Fig. Components of a Data Communication System

Message: The message is the information (data) to be communicated. It consists of text, numbers, pictures, sound or video or any other combination of these.
Sender: The sender is the device that ends the data message. It can be computer, workstation, telephone, handset, video camera and so on.
Receiver: The receiver is a device that receives the message. It can be a computer, work station, telephone, handset, television and so on.
Transmission Medium: The transmission medium is the physical path by which a message travels from sender to receiver. It can consists of twisted pair wire, coaxial cable, fiber-optic cable, laser or radio waves.
Protocol: A protocol is a set of rules that govern data communication. It represents an agreement between the communications, just as a person speaking French cannot be understood by a person who speaks Chinese.

Data Representation

Data is set of raw facts which are developed to turn up at the accurate information. There may be different structure in which data may be symbolized. Some of the forms of data used in communications are as follows:

Text: Text contains arrangement of alphabets in small case as well as upper case. It is accumulated as a pattern of bits. The common encoding systems are ASCII, Unicode
Numbers: Numbers contains arrangement of digits from 0 to 9. It is stored as a pattern of bits. The common encoding systems are ASCII, Unicode
Images: An image signifies thousand words. In computers images are digitally stored up.
Pixel: A Pixel is the least part of an image. The pixels signify the form of bits. Based upon the type of image (black n white or color) each pixel would require different number of bits to characterize the value of a pixel.
Audio: Data can be in the form of sound which can be recorded and transmitted. Example: The sound we hear on the radio is a basis of data or information.
Video: Video refers to showing of data in form of picture or movie.

18.4 Transmission of Data based on Communication technologies:

We can communicate with other devices by sending and receiving data. The data passes through the following devices. 1. Simplex 2. Half Duplex 3. Full Duplex

Simplex: In simplex mode of data communication, the data passed is one directional, like a one way road. The data is communicated and for the communication only one of the two stations on a link can convey the data at that time the other station can only receive the data. Keyboards and traditional monitors are both examples of simple devices.

Half Duplex: In half-duplex mode of data communication, the data can be passed from each of the station. The data can be received and broadcasted, but not at the same time. In this type of data communication only one device can send message at a single time, at that time the other device is only receiving the message. The half-duplex mode is like a one-lane road with traffic allowed in both directions. In this type of communication when the cars are going in one direction, the cars coming from the other direction has to wait. E.g. A walkie-talkie.

Full Duplex: In full-duplex mode of data communication, the data can be broadcasted and received at the same time. The full-duplex mode is like a two- way road with traffic running in both directions at the same time. In full-duplex mode, signals moving in one direction share the link with signals moving in the other direction and hence the sharing happens in two ways. One common example of full-duplex communication is the telephone network.

18.5 Transmission of Data based on Communication Technology Applications:

Electronic Mail

E-mail is an electronic mail. The messages are sent electronically through a network. The basic requirement for sending and receiving an email is that the user must have an email address. Using e-mail requires creating mailbox with an e-mail service provider. The mailbox is protected with a username and password.

Instant Messaging

Instant messaging is more on real time online communication between two users. It is also possible to send attachments as files. There is instant communication that is seen in Instant Messaging.

VoIP (Voice over Internet Protocol)

The VoIP technology has been developed for voice telephonic services in computer networks and on the Internet. There are service providers offering to replace regular telephones and phone lines with VoIP technology.

RSS

Really Simple Syndication (RSS) performs the function of delivering the content of a website in the form of a short description; the entire content can be accessed by clicking on the links. RSS content on a website is indicated by a special browser icon or graphical image on the site.

Blog

When a user or an organization posts information on a particular topic in an Internet site, that particular internet site is called as a blog. Information can be posted as views on the topic, by the people who are a part of the blog and also by visitors to the blog. Access to editing and creation of the blog’s content is protected with a username and password.

Podcast

Podcasting is the process of downloading the audio files that are prepared specially and are published on the Internet and listening to them on a portable media player. Podcasts generally comprises of a series of audio files.

Virtual Communities

A virtual community is a social online network created by using the Internet devices and technologies. One has to be registered to this particular website to access these services, e.g. Online chat rooms; Online multiplayer games; Social networking services like the Face Book with many features helping the users to post information, upload videos and publish photos

18.6 Transmission of Data on the basis of Communication devices:

Data is transmitted between two digital devices on the network in the form of bits. Transmission mode refers to the mode used for transmitting the data. The transmission medium may be capable of sending only a single bit in unit time or multiple bits in unit time.

When a single bit is transmitted in unit time the transmission mode used is Serial Transmission and when multiple bits are sent in unit time the transmission mode used is called Parallel transmission.

Based on Transmission Technology: Computer networks can be broadly categorized in to two types based on transmission technologies:

Broadcast networks: When a single communication channel is shared by all the machines, then it called as Broadcast networking. A broadcast network is a combination of services that provides live or recorded content such as movies, newscasts, sports, and public affairs programs that can be transmitted over a group of radio or television stations.

Point-to -point networks: When a communication has an end device and the networks are based on point-to-point communication such networks are called stations. The switching devices are called nodes. There are nodes that are connected to each other and others are attached to some stations. These switching nodes have no concern with the contents of data. Their function is to provide a switching facility that will allow data to move from one node to another till they reach the destination.

Based on Communication devices

A hardware device that is able of communicating a digital signal from the telephone, the communication wire or by a wireless mode. A striking example of a communication device is a computer Modem, which allows sending and receiving signals for interacting with other computers through the telephone. Wi- Fi devices, Network interface card acts as a good communication devices.

The different types of communications devices are:

Bluetooth: Bluetooth is the capability to connect a computer to a mobile without any wires or special connectors.
Modem: Modem is the hardware device that facilitates a computer to convey information over a telephone by exchanging the digital data to be made use by the computer into a signal used on phone lines and then reconverting it at the receiving end.
Router: A router is a smart device that can direct subnets jointly; routers are also used transversely to transfer the data across the world.
Hub: A hub is a non clever device; it sends messages from one port to all the ports at one time even if it’s not requested.
Switch: A switch is a clever device; it transmits data from one to the other port which is demanded this is quicker and safer device to use.
Network Interface Card: This is a device which is linked to a user’s computer that allows them to join their computer to a device.
Servers: A server is used in a network to provide the users of a network with many features.

18.7 Transmission of Data on the basis of Communication channels:

Transmission media can be made clear as physical passageway between transmitter and receiver in a data transmission system.

Guided Media

Transmission ability depends vitally on the medium, the length and if the medium is point-to-point or multipoint, e.g. co-axial, twisted pair, and optical fiber.

Unguided (Wireless) Transmission Medium

It offers a way for broadcasting electro-magnetic signals but do not direct them, e.g. wireless transmission. A network comprises of two or more computers that are connected to share resources (such as printers and CDs), replace files, or permit electronic communications. The computers on a network may be connected through cables, telephone lines, radio waves, satellites, or infrared light beams.

18.8 Transmission of Data on the basis of Network types:

A network comprises of two or more computers that are connected to share resources (such as printers and CDs), replace files, or permit electronic communications. The computers on a network may be connected through cables, telephone lines, radio waves, satellites, or infrared light beams.

LAN (Local Area Networks) :A local area network is a collection of computers linked to each other in a small area. The LAN’s are located in a building or a campus. LAN has the following characteristics:

Data transmitted at high rate.
The physical area covered by network is restricted.
The resources are joined with different methods.

A LAN structure consists of many Personal Computer terminals but a universal control terminal controls this network known as Server.

WANs (Wide Area Networks)

WAN has a larger coverage area, the locations are extremely high in number hence named as Wide Area Network.WAN can integrate LAN’s. WAN is able of covering the entire country or state for interactions. The railway reservation system, airline reservation system are examples of WAN.

WAN has the following characteristics:

The area enclosed is very big.
The data transmitted is slow in comparison to LAN.
The link media is normally a telephone line to be linked to LAN.

Internet

The Internet is an organization of associated networks that are universal in scale and assist data communication services such as remote login, file transfer, email, World Wide Web and newsgroups. With the soaring demand for connectivity, the Internet has become an interaction highway for millions of users.

Intranet

With the progress in the Internet, many private groups are executing intranets. An intranet is a private network make use of Internet-type tools, but accessible only in that organization. For bigger organizations, an intranet offers an easy access means to business information for employees.

MANs (Metropolitan area Networks)

The network smaller to WAN and larger to LAN is recognized as MAN (Medium size network). A model of MAN is a cable network inside a city. Cable network is getting TV programme from the satellite and it transmits to numerous user.

VPN (Virtual Private Network):

VPN uses a system known as channelling to transmit the data steadily on the Internet to a distant access server in your place of work system. Using a VPN assists you economically by using the open Internet as a substitute to long–distance phone calls to join strongly with your private network. There are two ways to create a VPN connection, by dialing an Internet service provider (ISP), or linking directly to Internet.

Comparing LAN,WAN,MAN

18.9 Let us sum up

Data communication is considered local if the communicating devices are in the same building or a similarly restricted geographical area and is considered remote if the devices are farther apart.
For data communication to occur, the communicating devices must be part of a communication system made up of a combination of hardware and software.
A Data Communication system has five components: Message, Sender, Receiver, Transmission Medium and Protocol.
Transmission of Data on the basis of Communication technologies- Simplex, Half Duplex, Full Duplex
Transmission of Data on the basis of Communication technologies applications – Email, Instant Messaging, RSS, VoIP, Blog, Podcast etc
Transmission of Data on the basis of Devices – Bluetooth, Router, Hub, Switch etc.
Transmission of Data on the basis of Channels – Guided and Unguided transmission channels
Transmission of Data on the basis of network types – LAN, MAN, WAN etc

you can view video on Data Communications and Networking Systems

References

Basic Networking Tutorial.
www.mof.gov.bt/publication/files/pub9ew3702mv.
Data Communication and Networks
nitttrc.ac.in/Four%20quadrant/dcn/Quadrant%20-%203/FAQ_PDF.pdf