INTRODUCTION TO COMPUTINGCHAPTER NO. 08

Data Communication and NetworksData Communication Data Transmission Modes (Simplex, Half –

Duplex and Full-Duplex)Forms of Data Transmission (Digital and Analog)Computer Networks and its AdvantagesTypes of Computer Networks Server and its typesNetwork topologies ( Bus, Star, Ring, Mesh etc)

Cont’d----

Data Communication and NetworksNetwork Devices (Hub, Switch, Repeater,

Router, Gateway etc)Telephone Networks (Dial – Up Lines and

Dedicated Lines)Communication devices (Modem and

Network Interface Card)Communication Channels (Physical and

Wireless Transmission Media)

Data CommunicationIt is a process of transferring data electronically

from one place to another.Data can be transferred using different medium.An electromagnetic or light wave used to transmit

data from one place to another is called a Signal.Communication of data from one place to another

place in the form of signals is called Transmission.The basic elements of data communication are:

Sender: A device that sends message, which consists of text, numbers, pictures etc, also called source or transmitter.

Data CommunicationMedium: The physical path that connects

sender and receiver, it is used to transmit data, the medium can be a copper wire, a fiber optic cable, microwave etc.

Receiver: A device that receives message, which is also called sink, it can be a computer, printer, or another computer related device, it must be capable of accepting the message.

Sender Receiver

Message

Medium

Data Transmission ModesIt is the way in which data is transmitted

from one place to another, there are three types of data transmission modes:

SimplexData can flow only in one direction, it cannot

be moved in both directions.It operates in a manner similar to on-way

street, the direction of flow never changes.A device with simplex mode can either send

or receive data, it cannot perform both actions.

Data Transmission Modes

An example is a traditional television broadcast, the signal is sent from transmitter to TV antenna, there is no return signal.

Half-DuplexData can flow only in both directions but not

at the same time, it is transmitted on-way at one time.

A device with half-duplex mode can send or receive data but not at the same time, therefore its speed is slow.

A B

Data Transmission Modes

An example is a internet surfing, the user issues a request for a web page, the web page is downloaded and displayed before the user issues another request.

Another example is Walkie-Talkie.Full-DuplexData can travel in both directions

simultaneously, it is faster than half-duplex.Time is not wasted in changing the direction of

data flow.

A B

Data Transmission Modes

A telephone is a full-duplex device, both persons can talk at the same time.

A B

Forms of Data TransmissionDigital Data TransmissionDigital signal is a sequence of voltage

represented in binary forms, these signals are in the form of electrical pulses of ON and OFF.

Digital signals are faster and efficient, they provide low error rates, high transmission speed and high-quality voice transmission.

All data communication between the computers is in digital form.

In digital signals high voltage is represented by 1 and low voltage is represented by 0.

Forms of Data TransmissionAnalog Data TransmissionAnalog signal is a continuous electrical

signal in the form of wave, which is known as Carrier wave.

Telephone line is the most commonly used media for analog transmission of data.

Light, sound, radio and microwave are also examples of analog signals.

Forms of Data Transmission

Analog and Digital Signals

Computer NetworksA computer network is a set of two or more

computers connected together in order to share information and other resources.

The computers in a network are connected with one another through cables, satellite or telephone lines.

Types of computers in a network are:Terminal / Client ComputerEvery computer that is part of a computer

network is called a terminal or node or client.The users using different terminal computers can

share information and send or receive data from one terminal to another .

Computer NetworksServer ComputerA server computer in a network is used as a central

computer which controls other computers in the network.

Server computers are more powerful than terminals.Examples of Computer NetworksComputer network can be used in an office, different

people in the office can access common information. If all user computers are connected through a

network, they can share their files and exchange mail, they can also send faxes and print documents from any computer in the network.

Computer NetworksAnother example of computer network is Internet,

in which millions of computers are connected through phone lines.

People using this network can share information, files and talk with one another.

Benefits of Computer NetworksData and information can be shared among

different users, resources like printers, scanners, CD-ROM drives, hard disks and software can also be shared.

People can save a lot of money by using the same software over a network instead of purchasing separate copy of the software for each user.

Computer NetworksA person can communicate with others very easily

using a large network like internet.Small computer networks allow multiple users to

share a single Internet connection.A network can manage the company’s critical data

in a better way, data can be centralized on shared servers instead of storing it on different computers.

Everyone can find the data easily, it becomes easier for the administration to take backup of data regularly.

Security can be implemented easily.Networks facilitate many types of games and

entertainment.

Types of Computer NetworksComputer networks are categorized

according to:How they are organized physically.The way they are used.The distance over which they operate.

Three main types computer networks are:LAN: Local Area NetworkWAN: Wide Area NetworkMAN: Metropolitan Area Network

Types of Computer NetworksLocal Area Network (LAN)LAN is the most common type of network, it

covers a small area.Most LANs are used to connect computers in a

single building or group of buildings.Hundreds or thousands of computers may be

connected through LAN, typical LANs can be found in industrial plants, office buildings and colleges or university campuses.

There are many types of LANs, Ethernet is the most common for PCs.

Types of Computer NetworksLANs are capable of transmitting data at

very fast rate, data transmission speeds of LANs are 1 to 100 Mbps.

It is much faster than data transmission over a telephone line, it can transmit data in a limited distance.

LAN is of two types:Peer-to-Peer LANClient-Server LAN

Types of Computer NetworksWide Area Network (WAN)It covers a large area, as it is used to connect

computers in different cities, countries and continents.

Normally a WAN consists of two or more interconnected LANs.

Computers in WAN are often connected through telephone lines, they can also be connected through satellites.

WAN can reach the parts of the world that are not possible with LANs .

Types of Computer NetworksThe speed of the WAN depends on the speed

provided by the company, transmission rate of WAN is typically 56kbps to 45 Mbps.

WAN is expensive than LAN, it is not as fast as LAN, it requires long cable distances and there is a possibility of error in data transmission.

The largest WAN in existence is Internet.

Types of Computer NetworksMetropolitan Area Network (MAN)It covers a geographical area of the size of a

city, it typically includes one or more LANs but covers a small geographical area than WAN.

A MAN often acts as a high-speed network, mobile phone systems often use MAN.

Server and its typesServers are the workhorses of the client -

server network, they serve network users and assist them to accomplish a variety of tasks.

The number and type of servers on a client-server network depend on the network size and workload.

Different types of servers are: Dedicated Server, Authentication Server and File Server.

Dedicated ServerIt is used to perform one specific function

such as handling e-mail, these servers perform such tasks that require a lot of time.

Server and its typesPrint Server - It manages the printing jobs, a

network with a centralized printing service will have a print server.

This server routes print jobs to appropriate devices, it also prioritizes printing according to order of request.

Application Server - It stores and distributes a set of application software to each system on the network.

The user upgrades and installs new software once on application server rather than deploying the programs throughout the organization.

Server and its typesDatabase Server - It manages the database of

an organization, it is dedicated to database storage, queries and retrievals.

Email Server - It handles a large volume of incoming, outgoing and internal e-mails, it remains connected to the internet, it may be located at any place in the world.

Communication Server - It handles all communication between the network and other networks, it also manages internet connectivity.

All requests for information from the internet and all messages being sent through internet pass through communication server.

Server and its typesE-mail servers, Web servers and other devices

needing to communicate with internet usually route all their traffic through communication server.

It provides a single point of contact with outside world and makes it easier to secure the network from hackers.

Web Server - It is used to host a Web site available through the Internet, they run specialized software that enables them to host Web pages.

Authentication ServerThis server keeps track of the users who log on the

network, it also keeps track of different services available to each user on the network.

Server and its typesAuthentication servers also act as overseers

for the network, they manage and coordinate the services provided by any other dedicated server located on the network.

File serversIt stores and manages files for the network

users, on corporate networks, employees are provided with space on a file server to store files.

Network TopologiesThe physical layout or the way in which network

connections are made is called a topology.It refers especially to the locations of computers

and how the cable runs between them.It is important to select the right topology for

proper use of computer networks.Bus TopologyThe simplest type of network is the bus

topology, in which all computers or network nodes are connected to a common communication medium.

In a local network, this medium is often a central wire called a bus.

Network TopologiesA collision can occur in bus topology if two

computers transmit data at same time.Bus topology is mostly used in Peer-to-Peer

networks.Working of Bus Topology If a computer wants to send data to other

computer in the network, it sends data and destination address via the bus.

The data and address moves from one computer to the other, each computer checks the address.

If it matches with the address of the computer, the computer keeps the data, otherwise the data moves to the next computer.

Network TopologiesAdvantages Simple, easy to use, and suitable for very small

networks.Least amount of cable is required to connect the

computers so it is less expensive.Easy to extend a bus, two cables can be joined

with a connector.Allowing more computers to join the network.DisadvantagesHeavy network traffic can slow a bus

considerably.Each connector reduces the strength of electrical

signals.

Network TopologiesA cable break or loose connector will cause

reflections and entire network will stop.As the number of computers increases, the

speed of the network slows down.

Network TopologiesStar TopologyA star network is one in which all the cables run

from the computers to a central location, where they are all connected to a device called Hub.

It is mostly used in Client-Server Networks.Working of Star TopologyIf two computers want to share data, the sender

computer sends data to the Hub sends it to the receiving computer.

Each computer on a star network communicates with a central hub, which provides a central connection point so that all computers can communicate across the network.

Network TopologiesAdvantagesIt is easy to modify and add new computers to a star

network without disturbing the rest of the network.Hub can accommodate multiple cable types.Finding faults become very simple.Single computer failure does not bring down the

whole network.It is more flexible among the remaining topologies. DisadvantagesIf central hub fails, the entire network breaks down.It is more expensive because all network cables

must be pulled to one central point.

Network TopologiesTree TopologyIt combines characteristics of bus and star

topologies. It consists of groups of star-configured

workstations connected to a bus backbone cable.

Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

AdvantagesPoint-to-point wiring for individual segments. Supported by several hardware and software

venders.

Network TopologiesDisadvantages of a Tree TopologyOverall length of each segment is limited by

the type of cabling used. If the backbone line breaks, the entire

segment goes down. More difficult to configure and wire than

other topologies.

Network TopologiesSTAR TOPOLOGY TREE TOPOLOGY

Network TopologiesRing TopologyIn this topology each computer is connected to next

computer with the last one connected to the first.Data flows around the circle from device to device in

one direction only.Ring topology is also known as Token ring topology.Its data transfer rate was originally 4Mbps or 16

Mbps, the recent token ring topology provides a speed up to 100 Mbps.

AdvantagesBecause every computer is given equal access to the

token, no one computer can monopolize the network.

Network TopologiesDisadvantagesFailure of one computer on the ring can affect

the whole network.Difficult to troubleshoot.Adding or removing computers disrupts the

network.Mesh TopologyIn this topology every device on the network is

physically connected to every other device on the network.

A message can be sent on different possible paths from source to destination.

It provides improved performance and reliability.

Network TopologiesMesh networks are not used much in local

networks, it is mostly used in wide area networks where reliability is important.

AdvantagesThe use of dedicated link guarantees that

each connection can carry its own data load, it eliminates the traffic problem.

If one link becomes unusable, it does not harm the entire system.

It is easy to troubleshoot.

Network TopologiesDisadvantagesA full mesh network can be very expensive.It is difficult to install and reconfigure.

Network DevicesHubIt is also called as Concentrator or Multi-

station Access Point (MAU) which provides central point for cables in a network.

It also transmits signals and have multiple ports to which devices are connected.

It broadcasts all messages to every computer on the network but only the intended recipient computer takes the message.

A hub can handle only one-way information traffic at a time.

Network DevicesSwitchIt is more intelligent device than hub, that uses

specialized hardware called an Application Specific Integrated Circuit (ASIC).

ASICs can run up to gigabit speeds with very low latency rates.

A switch connects computers into a network and sends messages only to the intended computer.

It can also handle multiple communication channels at the same time.

The type of communication in the switch is full-duplex.

Network DevicesWireless Access Point (WAP)It is a central device that allows computer and

other devices to transfer data wirelessly among themselves or to a wired network.

WAPs have high quality antennas for optical signals, some manufacturers suggest to place WAP at the highest possible location for the best signal.

RepeatersIt is a device that is used to connect network of

same types to boost the signal.A signal loses its strength as it passes along the

cable, called Attenuation, they transmit signal beyond the limit of communication media.

Network DevicesRoutersIt is a device that connects multiple networks using

similar or different protocols, it manages the best route between any two communication networks.

Routers are suitable for big Wide Area Networks, it can connect network of different countries, they send data in less time.

GatewayIt is a device that connects two or more networks

with different types of protocols, it is an intelligent device that can convert data according to the protocol.

It can connect a PCN to mainframe computer network.

Telephone NetworkPublic Switched Telephone Network (PSTN)

is the world wide telephone system that manages voice-oriented telephone calls.

This network uses digital technology except the link from company to home that is often analog.

It is also used in computer communications.Data, instructions, and information can be

transferred over the telephone network using dial-up lines or dedicated lines.

Telephone NetworkDial – up LinesIt is a temporary connection that uses the

analog telephone line for communication.A modem at the sending end is used to dial

the number of a modem at the receiver end.If there is a problem in any of two modems,

the communication stops.Dial – Up Line is inexpensive as it costs a

local call, it can be used to connect two or more computers located at any location.

The quality of dial-up lines is not very high.

Telephone NetworkDedicated LinesIt is a connection that is always established

between two communication devices, its quality is better than dial-up line.

It is used to connect two distant locations, these lines can be digital or analog.

The speed with which a line carries data and information is called transfer rate, which is expressed as bits per second (bps), Kbps, Mbps, Gbps etc. Its types are:

Integrated Services Digital Network (ISDN) Lines – provides faster transfer rates than dial-up lines for small business and home users.

Telephone NetworkIt is a set of standards for digital transmission

of data over standard copper telephone lines.One telephone line can carry three or more

signals at one time using the same line, this technique is Multiplexing.

ISDN requires ISDN Modems at both sides.Digital Subscriber Line (DSL) – uses standard

copper telephone for fast speed transmission, it is easier to install than ISDN and is also faster.

A special network card of DSL modem is required to connect to DSL.

Telephone NetworkCable Television Lines (CATV) – is not a standard

telephone line, it is very popular dedicated line used to connect to the Internet.

T - Carrier Line – is one of the many digital lines that carry multiple signals over a single communication line, they provide fast data transfer rates.

These line are expensive and only medium or large companies can afford them.

Asynchronous Transfer Mode (ATM) – is a service to carry voice, data, video, and multimedia, at very high speed, used by telephone networks, Internet, and other networks with heavy traffic.

Communication DevicesIt is a hardware device used to transmit data,

instructions, and information between a sending and receiving.

Example: Modem & NIC.Modem (Modulation demodulation) – it

converts digital signal to analog and analog signal to digital, it sends and receives data from one computer to another through telephone lines.

Its types are: External Modem, Internal Modem, Wireless Modem, ISDN Modem, DSL Modem, Cable Modem and Satellite Modem.

Communication DevicesNetwork Interface Card (NIC) – also called

LAN adapter, it is used to connect a device to a network.

It manages the transmission of data, instructions and information to and from the computer with NIC.

NIC works with particular network technology like Ethernet and token ring.

The transfer rate of an Ethernet card is from 10 Mbps to 1000 Mbps.

Different NICs are available for different types of computers.

Communication ChannelCommunication channel or Transmission media

is a path through which data is transmitted from one place to another.

In data communication the data signals are transmitted in the form of electromagnetic energy, combination of electric and magnetic fields vibrating in relation to each other.

A few types of media can support these signals, categorized as guided and unguided media.

Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current, while fiber-optic is a glass cable that accept and transport signals in the form of light.

Communication Channel

Guided MediaTwisted-pair cable consists of two conductors,

each with its own plastic insulation, twisted together, one of the wire is used to carry signals to the receiver, other is used only as a ground reference.

The number of twists per unit length determines the quality of the cable, more twists means better quality.

Two types of twisted-pair cable are used, unshielded twisted-pair (UTP) and shielded twisted-pair (STP).

STP cable has a metal foil or braided-mesh covering, that encases each pair of insulated conductors.

STP is more expensive than UTP, it was introduced by IBM.

Guided Media

Coaxial cable carries signal of higher frequency.

It has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of two.

Guided Media

A fiber-optic cable is made of glass or plastic and transmits signals in the form of light.

Optical fiber use reflection to guide light through a channel.

A glass or plastic core is surrounded by a cladding of less dense glass or plastic.

The difference in two materials must be such that a beam of light moving through the core is reflected off the cladding instead of being refracted into it.

Guided Media

Fiber composition

Guided Media

Unguided media transports electromagnetic waves without using a physical conductor, known as wireless communication.

Signals are normally broadcast through air.

Unguided Media

Radio waves are used for multicast communications, such as radio and television, and paging systems.

Unguided Media

Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

Unguided Media