Computer networks 2013

Transcription

1 Chapter 4 EXERCISE 1 1 Describe what is meant by each of the following: a Router b Bridge c Proxy server Answers: see the Glossary. 2 Many small businesses have computer networks. a List three advantages of networking computers. b List two disadvantages of networking computers. 1 Answers: see Chapter 7, Advantages and disadvantages of LANs. 3 a Describe a LAN you are familiar with. b Draw a map of the LAN showing all the computers connected to it and the cabling that connects them. Answers: you should draw a diagram similar to one of Figures 7.1 or 7.2 in the text book. This could be changed to show features of an actual network you use. If you use a computer room, you may also find it interesting to draw a scale diagram of this and draw the actual location of the network on it. 4 a Explain what is meant by a client/server network. b Explain what is meant by a peer-to-peer network. Answers: see the Glossary. 5 Wireless LANs are now being used in many homes and offices. a Name three essential components of a WLAN. Answer: Wireless access points attached to the network; wireless NIC; router. b Explain why you might choose to install a WLAN as opposed to a wired LAN. Answer: Any reasonable reason, for example:

2 WLANs may be installed instead of a wired LAN because: Access is more flexible. Users can access a WLAN from wherever they are working provided their computer is within range of the network and has a wireless NIC. If the user is moving around within range of the network, access can be maintained. A WLAN may be easier and cheaper to install because fewer cables are required. Electrical and network cables are usually embedded within the structure of the building and special provision has to be made for this. 6 Many large companies use WANs to transact business. a Explain what is meant by a WAN. Answer: A wide area network. This connects networks across a wide geographical area. b Give two methods of communication that a WAN may use. Answer: Networks may be made up of wired and wireless LANs and may use any network technology, including copper telephone lines, fibre-optic cable and wireless or microwave links. 7 Explain what is meant by the term bandwidth. Answer: see the Glossary. 8 Discuss the advantages and disadvantages to a home user of replacing dial-up Internet access with broadband. Any reasonable answer is acceptable. These may vary depending on the country you are working in and the type of broadband you have. In the UK, if you have broadband through a telephone line: Advantages of dial-up Internet access: You only pay for what you use and you use a normal telephone line. Disadvantages of dial-up Internet access: Slow web access. The telephone line cannot be used by someone else during Internet access for either telephone calls or Internet access for an additional computer. Advantages of broadband: Much faster web access. The normal telephone line is available in addition to broadband. Disadvantages of broadband: You pay a monthly subscription for connection. A highspeed broadband connection is not available everywhere in the UK. 2

3 2 1 Many individuals and organisations are connected to the Internet. a Describe what is meant by the Internet. Answer: see the Glossary. b List the hardware needed to connect to the Internet. Answer: For one computer to connect to the Internet from home using a telephone line, for a basic dial-up connection or for a broadband connection, you would need a computer with a NIC, a modem and a telephone connection. 2 Describe what is meant by an Internet Service Provider and explain why you would need one. Answer: An Internet Service Provider (ISP) is a company that is directly connected to the Internet and will give you access to it, usually for a fee. You need a subscription to an ISP so that you can access the Internet. 3 a Describe the benefits that can be gained by a company setting up its own website. Any reasonable answers, for example: Provision of information about its products for customers. Improved marketing of the company s products. Direct sales to customers via the website. b Describe what is meant by an intranet, and explain how this differs from the Internet. Answer: An intranet is a network similar to the Internet but only available to those working for a particular organisation or company. c Describe the benefits that can be gained by a company by setting up an intranet. Any reasonable benefit, for example: An intranet can be used as an information service to help employees follow the company s policies and practices. Employees can operate the company and resolve any difficulties without constant public exposure. 3

4 4 Describe what is meant by an IP address and explain why it is necessary. Answer: An IP address (Internet Protocol address) is a unique 32-bit address of a computer connected to the Internet. An IP address is needed to identify the computer so that it can be connected to the Internet. 5 Describe what is meant by TCP/IP and explain why it is necessary. Answer: for a definition of TCP/IP see the Glossary. TCP/IP is needed so that computers can communicate with each other over the Internet. 6 Describe what is meant by the following and explain what they are used for: a Hub b Bridge c Proxy server Answers: see the Glossary. 7 Many people use . a Describe what is meant by . Answer: see the Glossary. b Discuss the advantages and disadvantages of compared with the post. usually arrives faster than a letter sent in the post. This is especially true for long distances; for example, you would expect an to Australia from the UK to be very fast but a parcel might take several days. You need a computer and Internet access to send . These are expensive to buy and you need to know how to use them. You can send more documents by and the cost is the same whereas with the mail, the more you send the more it costs. You can send a wider variety of contents by mail; for example, you could send clothing, whereas with you can only send documents or other similar attachments. If you already have a computer and Internet access then is almost cost free, whereas with a letter you have to pay each time you send one and the cost relates to the size of the letter or parcel. c Discuss the advantages and disadvantages of using compared with the telephone. 4

5 5 With , it doesn t matter if the person you are trying to contact isn t there. You can send an at any time and this is saved until the recipient accesses their . To speak to someone on the telephone, they must be there (or you can leave voic , which is effectively spoken ). You need a computer and Internet access to send . These are expensive to buy and you need to know how to use them. A telephone is relatively cheap to buy and easy to use. You can send documents by whereas with the telephone you cannot send documents. If you already have a computer and Internet access then is almost cost free, whereas with a telephone call you have to pay each time you make a call and the cost relates to the distance covered. With a telephone call, you can have a conversation but with most communication has to be entered into a computer. You can send a wider variety of contents by whereas with a telephone call you can only speak. d You receive an with an attachment and want to send this to a friend. Describe what would happen if: i you replied to the Answer: The address of the person who sent it to you would be automatically entered in the To: field and any attachments would be dropped. ii you forwarded the Answer: No addresses would be automatically entered in any fields but the attachments would be retained. e Describe what is meant by contacts and how these could be useful when sending an . Answer: contacts are entries in an electronic address book: names, and postal addresses, telephone numbers, etc. for friends and colleagues, etc. Contacts can be used to quickly find the address of the person you are sending the to. 8 Describe what is meant by the following and briefly explain their purpose: a server b client Answers: see the Glossary.

6 10 Describe what is meant by the Internet and the World Wide Web. Identify the differences between them. The Internet is the hardware and networks that provide the physical means of communication. The Web is software that runs on the Internet and is a collection of interconnected, multimedia pages accessible using a web browser. 12 Describe what is meant by chat and explain why you might want to use it. Any reasonable answer: Chat is direct communication with a group of people by sending messages which are delivered immediately to everyone in the chat room. You might want to use it for socialising with a group of friends or organising a job with a work group. 13 a Describe what is meant by a search engine. Answer: see the Glossary. b Give the names of three popular search engines. Answer: Google, Ask Jeeves, Excite, etc. c Describe how information can be found on the Web by entering key words in a search engine. Search engines have indexes of the web addresses of information pages and brief descriptions of what is on the page and these are associated with key words. When key words are entered in the search engine, the web addresses and descriptions are retrieved from the index. 14 a State the name of a browser. Answer: Internet Explorer, Firefox, Netscape, etc. b Describe the purpose of a browser. A browser enables a user to access and view web pages. c List the main features of a browser and briefly describe what each is used for. Answer: List around ten features of a browser using this format: Feature: Favorite Used for: Storing the web addresses of pages that you want to access again. 15 Describe what is meant by online shopping and discuss its advantages and disadvantages. 6

7 Answer: Online shopping is shopping using the Web. You find what you want to buy, pay for it by credit or debit card, and it is delivered to your home by post or delivery van. Any reasonable advantages, for example: 7 A much wider range of goods is available. You may be able to specify what you are buying before it is manufactured. You don t waste time going round the shops only to discover none have what you want. Prices may be cheaper. You can read the comments of others who have bought the goods. Any reasonable disadvantages, for example You have to wait for goods to be delivered. This may take several days. You cannot see the goods beforehand. They may not be of the quality you expect. The goods may not arrive. Hackers may copy your credit or debit card and use it to defraud you. 16 Describe what is meant by online banking and discuss its advantages and disadvantages. Answer: Online banking is banking using the Web. You can look at your bank statements, pay money to other online accounts and receive payments. Any reasonable advantages, for example: You can access all your bank details without going to a branch of the bank (if there are any). You access your bank account over the Web so it can be more private. It is easier to invest in a wider range of bank and savings accounts. You can set up payments to others in advance so you don t forget to pay. Any reasonable disadvantages, for example: You have to use a cashpoint to withdraw cash. Cheques can only be paid in by post or at a branch of the bank. If you need advice from your bank, you can only get this by telephone or . You have to have a computer with internet access. 17 Explain the difference between uploading and downloading. Answer: see the Glossary. 18 With the aid of examples, explain what is meant by phishing.

8 Answer: see the Glossary. You may find real examples in your inbox. 19 Describe each component part of this URL: Answer: http is the type of resource and this is a web page. is the domain name of the host computer and this is an international commercial organisation. community is a directory or folder on the host computer. index is a filename..htm is an extension and this shows that the file contains HTML (Hyper Text Mark-up Language). Exercise In this question you will consider how you communicate by telephone, chat and video conferencing. a Describe how each of telephone, chat and video conferencing allow you to communicate instantly with another person. Telephone you enter someone s number into a telephone and it rings. If they answer, you can talk to them in real time, otherwise you can leave a message on voic . Chat you log on to a chat room and can send short messages to any other members of the chat room who are also currently logged on. Video conferencing you make contact with someone, for example, using Skype you dial their number. Video conferencing is like using a telephone except that you can see the person speaking to you. b Find out the cost of installing and running the technology needed to allow you to communicate by each of telephone, chat and video conferencing. Any reasonable answer, for example in the UK: Telephone you have to pay for installation, monthly line rental and each call made unless it falls within the free call time of your contract. Chat you have to pay for a computer and Internet access. 8

9 9 Video conferencing there are several popular methods. Using Skype, you have to pay for a computer and Internet access. Skype is free to download. Skype-to-Skype video calls are free. There are other similar products and services available. c State which of these methods of communication give you the most personal contact. Give reasons for your answer. Video conferencing is the most personal because you can have a spoken conversation (as you can with a telephone) but you can also see the person you are speaking to. d You are working on your computer preparing a word processed essay. You want to communicate with a friend as you are doing this. State which of these methods of communication you would use. Give reasons for your answer. Chat may be less distracting because it is effectively in real time. You are alerted when your friend has something to say but you do not have to respond immediately. e You are working at home and want to communicate with a colleague at your head office. State which of these methods of communication you would prefer to use. Give reasons for your answers. You may prefer chat for the reasons given in d) above. You may want to avoid video conferencing as you may want to keep your home life private and dress codes at work and at home are often different. f You are working on a product design with others in your project team. The team wants to talk to a technical design expert who has expertise that the team does not have. All the team want to ask the expert questions. State which of these methods of communication you would use. Give reasons for your answer. You are likely to prefer video conferencing so that everyone can be involved, are able to question the expert directly, can listen to the responses of the expert and have the opportunity to ask further questions. If the expert is only available for a short time, this will maximise the project team s contact. g A class of school pupils wants to talk to another class in a school on the other side of the world. State which of these methods of communication you would use. Give reasons for your answer.

10 Pupils will probably want to see and talk to each other, and as it is one class talking to another, a video conference with a large screen projector could be most effective. If the classes are to cooperate to complete a project together, and will need group discussion over a prolonged period between groups and individuals within each class, then it is worth considering using chat. 1 What is a LAN? Revision exercises answers Answer: Local Area Network A LAN is a collection of computers connected together within a small geographical area so that they can share information and peripherals and also communicate with each other. 2 Describe three different security threats to web users. Describe each threat and say how you would reduce the impact of it. Threat Viruses. These can be spread by downloading infected or programs from the Internet. Spam. This is unsolicited that can overwhelm appropriate use of . Phishing. This is an attempt to find out personal information, for example, bank card numbers, account numbers and usernames and passwords for online banks. These are then used for identity theft and fraud. This is done by sending a fraudulent that pretends to be from the bank. Way to reduce the impact Use antivirus software. Use a spam filter. Do not reply to the . Delete it. If you are worried by the content of the then contact the bank independently; for example, log on to the bank s website in the usual way and use the bank s web mail to contact them. 3 Compare and contrast the Internet and the Web. 10 Internet The Internet is a network of networks that connects computers. Web The World Wide Web consists of many millions of web pages.

11 The Internet consists of the hardware and networks that connect computers all over the world. To connect to the Internet you need a personal computer or workstation, a modem, a communications link such as a telephone line and access to an Internet service provider (ISP). To transfer data from one computer to the next, computers must follow a set of rules called a protocol. The protocol used over the Internet is TCP/IP (Transfer Control Protocol/Internet Protocol), which allows operating systems software from different computers to communicate. The Web is software. You need a browser such as Microsoft Internet Explorer or Mozilla Firefox in order to view web pages. Web pages are usually written in HTML, although other languages may be used, such as Java. You can view a web page by entering its unique web address or URL (Uniform Resource Locator) in a browser. 4 Why is an IP address needed? An IP address is needed so that each computer on the Internet has a unique address that identifies it so that information can be sent to it. 5 Which of the following could be valid web addresses? Yes No No Yes No Yes Yes 6 Briefly describe ten services available on the Web. Services available on the Web include: 11 View hundreds of millions of web pages, all over the world. Use a search engine to find the pages you want. Send and receive . Online shopping and banking. Customer support. Software downloads. Mailing lists, bulletin boards and newsgroups.

12 Chat and conferencing. Web rings. Web broadcasting. You can set up your own website, which could advertise your business. You can upload and download digital media, such as music, images and video, and publish these on the Web so that they can be shared with friends and family. Blogs are on line personal diaries with narrative, pictures and hyperlinks that you can publish on the Web. Wikis enable you to describe and define particular topics in collaboration with other web users. Social networking sites allow you to communicate with friends. 7 a Describe three ways to find information on the Web. Surf, use a directory service and use a search engine. b Describe how you would use each of the three ways to find information. Surf click on hyperlinks until you find what you are looking for. Directory service select categories and these become more and more relevant as you get closer to the information you need. Search engine enter keywords and use Boolean logic so that you make your search as well targeted as possible. 12