Chapter 4 : Computer Network (Part 2)


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computer networks and communications lesson 67 introduction to computer networks and communications computer network a computer network is a system of interconnected computers and peripheral devices for example it may connect computers printers scanners and cameras us 151


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ing hardware and software these interconnected computing devices can communicate with each other through defined rules of data communications in a network computers can exchange and share information and resources a computer network may operate on wired connections or wireless connections when two or more networks are linked or connected and are able to communicate with one another using suitable hardware and software it is called an internetwork 152


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communications communications is about the transfer of information from a sender across a distance to a receiver using electricity radio waves or light information and data in the form of codes are transmitted through a physical medium such as wire cable or even the atmosphere the information that is transmitted sent can be text voice sound video graphics and images or a combination of all these which we call multimedia we transmit information or data by using two types of signals namely analog and digital computers communicate with digital signals the older forms of communications technology such as telephones and radios use analog signals therefore in order to make 153


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communications possible from computers across telephones and radios and back to computers and other digital devices again there must be a signal translator which we call ­ a modem the modem which is short for modulator or demodulator converts digital signals into analog and back again into digital signals for information to move across the telephone line connections for networking communications among computing devices in a network can only happen through defined rules of communications and connections in general for communications in a network to be possible there must be a physical medium ­ to allow data to travel across it from device to device a set of rules called protocols to ensure that interconnected computing devices have the same standards for exchange of information to occur smoothly a system application for managing network information flow to ensure that data transmission sent from one device is received by the intended receiver if any of these levels of connectivity is missing communications for networking will not be possible for example if the physical medium is cut off there will be no communications if protocol between interconnected devices are not the same data transmission will not be understood between devices if there is no network management application 154


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available there will be no means of ensuring that information from one device will be sent to the correct receiving device protocol often simply referred to as a protocol a communications protocol is a set of rules or standards designed so that computers can exchange information with a minimal errors lesson 68 components of communications introduction in order for a network to properly operate two categories of network communications components are needed hardware and software computers hub switch router network interface cards and both wired and wireless communications media fall under the hardware category operating systems and applications fall under the software category 155


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network communication channels signals which carry information in a communications system travel through a physical medium this physical medium is called a communications channel or at other times a communications link a communications line or a communications medium some common types of network communications channels are the twisted-pair wire coaxial cable fiber-optic cable satelite systems wireless systems namely using radiowaves microwaves and infrared communications channels provide the most basic level of connectivity medium for a network network interface cards and networking devices the network interface card or nic is one of the most important communications devices for a pc 156


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the nic provides connection between the computer and the networks communications media this connection is necessary because the nic functions as a data conversion device to move data from the pcs system to the network medium and vice versa the network interface card also supplies the basic addressing system used to get data from pc to pc across a network the other hardware component that is required for communications to work on a network is the networking device such as the hub switch router and even the modem the function of these devices is generally to control the flow of data on a network network software 157


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how do computers communicate on a network once we have got the necessary hardware set up for a network we will need to have suitable software on the network computers that would be able to provide some basic functions such as connecting to other computers on the network sharing resources and files and providing for network security for users who are online in general a network software must be able to handle networking protocols and connections within the network and with other networks most importantly it should also provide file systems functions to organise disk space on the network computers for sharing purposes since most computer networks are connected to the internet a network software must have some form of management and security services to protect the network as well as computers on the network from unauthorised access lesson 69 158


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application software advanced features of presentation software networking and communications technology is fast changing the way people view society and how we plan our daily social activities through networking technology alone many today are finding friends online visiting a library in another country some people are able to go to the banks after they are closed as well as getting the latest development in news from within and outside the country mobile communications today is also based on the networking technology surfing the internet is not only limited to the desktop computer users but also those who have mobile phones with wireless technology at present there are more than 7 million such users across the world the internet has helped science and medical research progress further as doctors and researchers from anywhere in the world can contribute and cooperate in any problem brought to their attention technological solutions can be discovered quickly as individuals come forward to offer their help through the internet homemakers students teachers business people and almost anyone with access to networked computer go online and continue their path of lifelong education anywhere anytime organisations and individuals can make connections and establish communications within seconds with people nearby or overseas online communities can be formed and important issues and opinions to difficult problems can be discussed without a threatening environment all these are now possible because of networks and communications technology 159


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importance of networks and communications information is now made easy with the availability of network communications in a clinic for example network communications plays an important part in keeping patients database for easy retrieval unlike in conventional practice doctors and nurses have to look for a patients personal file from hundreds or maybe thousands of records with network communication the clinic saves time and manpower allocation can be effectively planned e-business e-business or electronic business refers to conducting business transactions on the internet not only limited to buying and selling but also servicing customers and collaborating with business partners e-business supports many types of business transactions including online shopping selling and renting users can browse the website and choose from the list of items or services to buy payment is usually via credit card online education 160


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with a network connections online education is made possible students at any location around the world can participate in an online classroom download tutorial questions and submit their assignments e-banking e-banking or electronic banking is the most popular banking facility nowadays it handles all types of banking transactions like account management fund transfer and payments primarily over the internet user can pay bills check the account balance and transfer money to other parties using ebanking facilities twenty four hours a day and seven days a week with e-banking most of the transactions can be done at home or from the office thus users save time on traveling and queuing at the bank counters long distance communication long distance communication is made easy via network availability communication is possible via voice text or video the cost of having this type of communication is cheaper than making a normal phone call and definitely faster and more effective than corresponding via letters of fax in business important decisions can effectively made through video conference meeting lesson 70 types of networks types of networks three types of networks 161


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local area network or lan metropolitan area network or man wide area network or wan here lan the email system within the school lab in smk kl man the email system within kl city wan the email system between kl and london a lan covers a small region of space typically a single building a man is a collection of lans with the same geographical area for instance a city a wan can be a collection of lans or mans or the mix of two with a very large geographical area for instance a country or even beyond the border lesson 71 local area network lan local area network lan is the smallest network compared to the other two networks 162


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the simplest form of lan is to connect two computers together lan is operated within a limited physical area such as at home school a single building or several buildings a network which consists of less than 500 interconnected devices across several buildings is still recognised as a lan inexpensive hardware used in lan previously include twisted pair coaxial cables and the higher end is fiber optic or wireless however coaxial cables are now being replaced by a higher speed cabling system such as cat5 using rj45 connectors lan is a very high speed network from previously 10mbps to 100mbps which is faster than man and wan local area network is a group of computers and network devices connected together usually within the same building lesson 72 metropolitan area network man first you have to understand the word metropolitan metropolitan describes important cities such as kuala lumpur manila singapore tokyo london and new york 163


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man is a network of computers located at different sites within a large physical area such as a city companies that have several branches within the kuala lumpur city such as banks might find a man useful to them in this case setting up a man across long distances can be best connected using fiber optics sometimes a man can be a collection of several lans within the same city man often acts as a high speed network although not as fast as a lan to allow sharing of regional resources man can be defined as a group of computers and network devices connected together within a large physical area lesson 73 wide area network wan wide area network wan is the largest network of all network types the internet is the largest wan in the world wan generally covers large distances such as states countries or continents an example in the society using wan is the banking organisation local banks have always maintained their business online by connecting all computers of their branches in the countries international banks also use wan to connect their computers all over the world actually wan is a group of mans or lans or the mixture of both networks 164


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a device called a router is the mans and lans all over a a router is a special that connects two or more and keeps data flowing a router makes all the different networks communicate such as connecting lan to lan lan to wan or wan to wan the transmission media in wan uses the fibre optic cable.wan is still considered a fast network with speeds 20 ­ 2000 kbps but slower than lan and man needed to connect large physical area networking device different networks between them lesson 74 differences between types of network setting up cost setting up a man network is more expensive than a lan but less than a wan managers have to consider the cost of buying the necessary hardware software medium and maintenance service for the desired network network size the network size of a man falls between lan and wan as you know a lan usually covers only a limited area such as a school lab a man will cover a greater area such as a city while a wan will cover the largest geographical area such as the size of malaysia speed lan offers the best speed in transmitting information followed by man and wan in addition lans are capable of transmitting data at very fast rates much 165



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