NETWORKS. (b) A person watches a film streamed from a website on a tablet computer.

Transcription

1 NETWORKS QUESTION 1 (a) Explain the term bit streaming. (b) A person watches a film streamed from a website on a tablet computer. (i) Give two benefits of using bit streaming for this purpose. (ii) State two potential problems of using bit streaming for this purpose (c) Explain the terms on-demand bit streaming and real-time bit streaming. ANSWER 1 (a) - sequence of digital signals / bits - over a communication path / Internet - transfer of data at high speed - requires fast broadband connection - requires some form of buffering - bits arrive in the same order as sent (b) (i) (ii) - no need to wait for a whole file to be downloaded - no need to store large files on user s computer - allows on demand playback - no specialist software is required for playback in browser - video stops / hangs if very slow Internet / broadband speed low - video stops / hangs if inadequate buffering capacity - loss of Internet means can t access films / files - may require specific software to run the files / films - viruses can be downloaded from the websites (c) on-demand - digital video tape, analogue video tape, or digital files are converted to bit streaming - format for broadcasting on the net; this is known as encoding, these encoded streaming video files are then uploaded to a dedicated server - a link for the encoded video is placed on a web site - a user clicks on the link to download the encoded streaming video; the streamed video is - then broadcast to the user as and when they require it - can be paused / can go back and re-watch / fast-forward, etc. real-time - an event is captured live with a video camera - the video camera is connected to a computer - the video signal is converted to streaming media files (encoded) on the computer REVISION 9608 SECTION 1 1

2 - the encoded feed is then uploaded from the computer to a dedicated streaming server via cable, DSL, or a high-speed internet connection - the server then sends the live images it to all users requesting it as real-time video streaming - cannot be paused etc QUESTION 2 A company operates a chemical plant, which has a number of processes. Local computers monitor these processes and collect data. The computers transfer these data to a central computer 50 km away. A telecommunications company (telco) provides cables. Engineers at the telco had to decide which type of cable to use. They considered the use of either copper cable or fibre optic cable. State two benefits of each type of cable. Each benefit must be clearly different. ANSWER 2 Benefits of copper cable copper cabling is less expensive to install copper cable is easier to install because it is more flexible it is easier to make terminations using copper cabling the expertise in use of copper cabling is more extensive has been around for years so very little is unknown about installations using this type of cabling Benefits of fibre optic cable fibre optic cables have greater bandwidth fibre optic cables need less signal boosting // can transmit over longer distances fibre optic cables have greater security (more difficult to tap into) fibre optic cables are immune to electromagnetic and other effects fibre optic cabling is lighter in weight (easier to install) fibre optic cables consume less power QUESTION 3 (a) Telephone calls can be made by using: conventional telephones (using the Public Service Telephone Network (PSTN) system) over a wired network a computer, equipped with speakers and microphone, connected to the Internet Put a tick () in the correct column to match each description to the appropriate communication method. (b) Distinguish between the Internet and the World Wide Web (WWW). (c) Name the hardware device that is being described: (i) A device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route. REVISION 9608 SECTION 1 2

3 (ii) A device used between two dissimilar LANs. The device is required to convert data packets from one protocol to another. (iii) A device or software that provides a specific function for computers using a network. The most common examples handle printing, file storage and the delivery of web pages. ANSWER 3 (a) (b) Internet massive network of networks/interconnected network of computer devices Internet stands for Interconnected Networks uses TCP/IP protocol World Wide Web (www) is a collection of (multimedia) web pages/documents...stored on websites http/protocols used to transmit data web pages are written in HTML URLs specify the location of the web pages web documents are accessed using browsers (c) (i) router (ii) gateway (iii) server REVISION 9608 SECTION 1 3

4 QUESTION 4 (a) (i) Describe what is meant by a client-server model of networked computers. (ii) Give two benefits of using the client-server model. (b) The diagram shows a computer network with connection to the Internet. Name the hardware device labelled X. ANSWER 4 (a) (i) at least one computer used to serve other computers are referred to as clients server provides services / applications etc. which may be requested by clients (ii) files and resources are centralised creation of security / manage security user needs user name and password to access network centralised back-up intranet capability Internet monitoring clients can be less powerful machines, therefore less expensive to buy saving resources on server reduces the burden on the client (b) Router QUESTION 5 What is a Server? ANSWER 5 Server is a computer program running to serve the requests of other programs, the clients. Servers are software programs that in most cases run off normal computing hardware. Server software includes: Printing File sharing Game hosting Websites Other web services REVISION 9608 SECTION 1 4

5 QUESTION 6 What is a Client? ANSWER 6 Client is an application or system that accesses a service made available by a Server. Clients are software programs and processes that connect to servers, sending requests and receiving responses. Client examples include: Web browser page requests Chat systems on mobile phones Online games QUESTION 7 Clearly describe the Client-Server model. ANSWER 7 As an example of modern client server model consider a video sharing website. The website has a server that stores all the videos that are uploaded to the site. The website is used by millions of clients a day and each of them connects to the servers to watch videos. When a client connects to the server, and asks for a particular video, the server loads the video into RAM from a large array of hard disks, and sends the video to the client. The client on receiving the video presses play and watches the video. Note: Other examples of Client-Server model are Shared Printing Service and Cloud Computing. QUESTION 8 Briefly explain how Internet works. ANSWER 8 When you want to send a message or retrieve information from another computer, the TCP/IP protocols are what make the transmission possible. Your request goes out over the network, hitting domain name servers (DNS) along the way to find the target server. The DNS points the request in the right direction. Once the target server receives the request, it can send a response back to your computer. QUESTION 9 What is a Network Gateway? ANSWER 9 A network gateway is an internetworking system capable of joining together two networks that use different base protocols. A gateway can be implemented completely in software, completely in hardware, or as a combination of both. On home networks, a broadband router typically serves as the network gateway. QUESTION 10 What is a Router? ANSWER 10 Routers are small physical devices that join multiple networks together. REVISION 9608 SECTION 1 5

6 Technically, a router is a gateway device, meaning that it connects two or more networks. Home networks typically use a wireless or wired Internet Protocol (IP) router. An IP router such as a DSL or cable modem broadband router joins the home s local area network (LAN) to the wide-area network (WAN) of the Internet. QUESTION 11 What is a Web Server? ANSWER 11 In general, all of the machines on the Internet can be categorized as 2 types: Servers and Clients. Those machines that provide services (like Web server or FTP servers) to other machines are servers. A server machine provide one more services on the Internet. For example, a server machine might have software running on it that allows it to act as a Web server, an server and an FTP server. QUESTION 12 What is a DNS? ANSWER 12 It s like your computer s GPS for the Internet. Its basic job is to turn a user-friendly domain name like Google.com into an Internet Protocol (IP) address like that computers use to identify each other on the network. QUESTION 13 Explain how communication systems are used to support the Internet: Telephone Network (PSTN), dedicated lines, cell phone network. The Public Service ANSWER 13 PSTN is the world s collection of interconnected voice-oriented public telephone networks. In relation to the Internet, the PSTN actually furnishes much of the Internet s long-distance infrastructure. Because Internet service providers (ISPs) pay the long-distance providers for access to their infrastructure and share the circuits among many users through packet-switching, Internet users avoid having to pay usage tolls to anyone other than their ISPs. REVISION 9608 SECTION 1 6

7 Many cell phone service providers offer mobile Broadband Internet Access Services for smartphones, basic phones, tables, netbooks, USB modems, mobile hotspots and other wireless devices over their 3G and 4G broadband networks. QUESTION 14 Explain the benefits and drawbacks of using radio waves. ANSWER 14 Radio waves are an electromagnetic radiation with differing wavelengths. They are used for many processes (broadcast TV, communication between satellites, enables computers to share information without wires, etc.) Radio waves have a large wavelength so they experience less interference and can travel over large distances. However, since they do not have a high frequency, they cannot transmit as much data. They can carry more signals than wires. QUESTION 15 Explain the benefits and drawbacks of using Microwave. ANSWER 15 Microwave transmission refers to the technology of transmitting information by the use of electromagnetic waves whose wavelengths are measured in centimeters; these are called microwaves. Microwaves are widely used for point-to-point communications because their small wavelength allows antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allow nearby microwave equipment to use the same frequencies without interfering with each other. The high frequency of microwaves gives the microwave band a very large information-carrying capacity. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains. It is also affected by anything blocking the line of sight, such as rainfall. QUESTION 16 Explain the benefits and drawbacks of using Satellite. ANSWER 16 A satellite is any object that revolves around a planet in a circular or elliptical path. Satellites have many purposes including data communications, scientific applications and weather analysis. Satellite transmission requires an unobstructed line of sight. The line of site will be between the orbiting satellite and a station on Earth. Satellite signals must travel in straight lines but do not have the limitations of ground based wireless transmission. REVISION 9608 SECTION 1 7

8 QUESTION 17 What is a Bitrate? ANSWER 17 A bitrate is a term used to describe the amount of data that is being passed within a given amount of time. Common measurements of bitrate include: Kbps and Mbps (meaning kilobits per second and megabits per second). A higher number is generally good, indicating high speed or high quality. When it comes to Internet speeds, a higher bitrate is always desirable. With higher bitrates, you can do more with your Internet connections: stream high-definition movies, play online games, download large files. REVISION 9608 SECTION 1 8

9 IP ADDRESSING QUESTION 1 (a) The table shows four statements about IP addresses. Tick () to show which of the statements are true. (b) Consider the URL: (i) Give the meaning of the following parts of the URL. (ii) Sometimes the URL contains the characters %20 and?. Describe the function of these characters ANSWER 1 (a) (b) (i) http enables browser to know what protocol is being used to access information in the domain cie.org.uk cie.org.uk is the domain name computerscience.html actual web page / file being viewed (ii) %20 because not allowed in a URL, %20 is the coding for a space (32 in denary)? separates the URL from all parameters or variables QUESTION 2 Briefly explain the term IP Address. ANSWER 2 An IP address (Internet Protocol Address) is an exclusive number that all IT devices (printers, routers, modems, etc.) use which identifies and allows them the ability to communicate with each other on a computer network. REVISION 9608 SECTION 1 9

10 IP addresses are binary numbers, but they are usually stored in text files and displayed in humanreadable notations, such as QUESTION 3 Briefly explain the IP Address formats. ANSWER 3 Originally IP addresses were divided into 5 classes (A-E). Classes A, B and C are the most important: the initial bits determine which class an address belongs to, and the classes differ in how much of the address is taken up with the network address and how much with the host address. QUESTION 4 What is a Public IP Address? ANSWER 4 A Public IP Address is assigned to every computer what connects to the Internet, where each IP is unique. In this case, there cannot exist 2 computers with the same public IP address all over the Internet. This addressing scheme makes it possible for the computers to find each other online and exchange information. Users have no control over the IP address (public) that is assigned to the computer. The Public IP address is assigned to the computer by the ISP (Internet Service Provider) as soon as the computer is connected to the Internet Gateway. A Public IP address can be either Static or Dynamic. A static public IP address does not change and is used primarily for hosting web pages or services on the Internet. A dynamic public IP address is chosen from a pool of available addresses and changes each time one connects to the Internet. REVISION 9608 SECTION 1 10

11 QUESTION 5 What is a Private IP Address? ANSWER 5 A Private IP Address is considered private if the IP number falls within one of the IP address ranges reserved for private networks such as a LAN (Local Area Network). Private IP addresses are used for numbering the computers in a private network including home, school and business LANs in airports and hotels which makes it possible for the computers in the network to communicate with each other. Devices with private IP addresses cannot connect directly to the Internet. Likewise, computers outside the LAN cannot connect directly to a device with a private IP. It is possible to interconnect 2 private networks with the help of a router. If the private network is connected to the Internet (through an Internet connection via ISP), then each computer will have a private IP as well as a public IP. Private IP is used for communication within the network whereas the public IP is used for communication over the Internet. Most Internet users with a DSL connection will have both a private as well as a public IP. QUESTION 6 What is a DNS server? ANSWER 6 A DNS (Domain Name System) manages public names of Websites and other Internet domains. DNS allows you to type names into your Web browser like soundcloud.com and your computer to automatically find that address on the Internet. A key element of the DNS is a worldwide collection of DNS servers. A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address and contains a database of network names and addresses for other Internet hosts. QUESTION 7 (a) An IP address has the following value: (i) Write the above IP address in hexadecimal. (ii) Explain the format of an IP address (b) Study the following sentence: When a user enters a URL into their web browser, the DNS service locates the required resource. Explain how a URL and DNS are used to locate a resource. ANSWER 7 (a) (i) 0B F F. 5 A (ii) composed of four (denary or Hexadecimal) integers each in the range 0 255/00 FF each stored in 1byte/8 bits/stored in 32bits (in IPv4) separated into network ID and host ID (b) URL = uniform resource locator reference address to a resource/website on the Internet REVISION 9608 SECTION 1 11

12 includes protocol used /includes domain name browser software sends URL to DNS DNS = Domain name system // Domain name service // Domain name server the true domain name (e.g. cie_exams.co.uk) is resolved/turned into an IP address by DNS DNS server stores a database/list of URLs with matching IP address a DNS server may need to pass a request onto another DNS server, (if URL not in its database) DNS server adds returned IP address and URL to its cache/database DNS server may return an error message if requested domain name is invalid or does not exist the DNS service has a hierarchy/or by example DNS server returns IP address to browser REVISION 9608 SECTION 1 12

13 CLIENT- AND SERVER-SIDE SCRIPTING QUESTION 1 A web page offers a link for users to request another web page. The requested web page contains HTML code and JavaScript code. Put each statement in the correct sequence by writing the numbers 1 to 5 in the right-hand column. ANSWER 1 QUESTION 2 The website offers help and advice about personal well-being. The website has a link Calculate my BMI that users can click to work out their Body Mass Index. When the Calculate my BMI link is clicked on the client computer, this webpage is requested REVISION 9608 SECTION 1 13

14 Loading the webpage produced this sequence of dialogue boxes: (a) Which lines in the webpage script are JavaScript code? (b) (i) Give the identifiers of two variables which have been used by the programmer. (ii) What group of program statements are performing selection? line number.. up to line number.. (c) By studying the web page script and its use, what is the use in JavaScript of: (i) the prompt function? (ii) the alert function? REVISION 9608 SECTION 1 14

15 (d) Put five of these statements in the correct sequence to describe how the content of the page shown is displayed by the client computer s browser software. Two of the statements will not be used. A The client computer processes the JavaScript code. B The page content is transmitted to the client computer. C The page is displayed on the client computer. D The user clicks on the hyperlink and the web page is requested from the network file server. E The web server processes the JavaScript code. F The user clicks on the hyperlink and the web page is requested from the web server. G The server finds the web page. The sequence is: (fill in the letters) (e) How is this JavaScript code run? (f) The web developer tested the JavaScript code without involving the web server. Explain how this is possible. ANSWER 2 (a) lines (b) (i) myweight myheight mybmi (ii) Line Number (c) (i) prompts the user for input assigns the input to the given variable (ii) displays the text shown in a dialogue box with the alert symbol (d) F G B A C (e) The browser will have an interpreter to execute the JavaScript code. (f) The browser loads the page from the local hard drive. REVISION 9608 SECTION 1 15

16 QUESTION 3 Explain the term Scripts. ANSWER 3 A script is a set of instructions. For Webpages they are instructions either to the Web browser (client-side scripting) or to the server (server-side scripting). Scripts provide change to a Webpage. All log on systems, some menus, almost all photograph slideshows and many other pages use scripts. QUESTION 4 Client-side: describe the sequence of events executed by the client computer and web server when a web page with embedded client-side code is requested and displayed by a browser. ANSWER 4 The client is the system on which the Web browser is running. JavaScript is the main client-side scripting language for the Web. Client-side scripts are interpreted by the browser. The process with client-side scripting is: 1. The user requests a Web page from the server 2. The server finds the page and sends it to the user 3. The page is displayed on the browser with any scripts running during or after display So client-side scripting is used to make Web pages change after they arrive at the browser. It is useful for making pages a bit more interesting and user-friendly. QUESTION 5 Server-side: describe the sequence of events executed by the client computer and web server when a web page with embedded server-side code is requested and displayed by a browser. ANSWER 5 The server is where the Webpage and other content lives. The server sends pages to the user/client on request. The process is: 1. The user requests a Webpage from the server 2. The script in the page is interpreted by the server creating or changing the page content to suit the user and the occasion and/or passing data around 3. The page in its final form is sent to the user and then cannot be changed using server-side scripting. The use of HTML forms or clever links allow data to be sent to the server and processed. The results may come back as a second Webpage. Server-side scripting tends to be used for allowing users to have individual accounts and providing data from databases. It allows a level of privacy, personalization and provision of information that is very powerful. REVISION 9608 SECTION 1 16

17 QUESTION 6 Recognise and identify some Javascript code. ANSWER 6 JavaScript Code and Blocks JavaScript code is a sequence of JavaScript statements. Each statement is executed by the browser in the sequence they are written. JavaScript statements are grouped together in a block. Blocks start with a left curly bracket and ends with a right curly bracket. The purpose of blocks is to make the sequence of statements execute together. JavaScript operators Arithmetic operators Assignment operators Comparison operators Logical operators Conditional operators Alert Box An alert box is often used if you want to make sure information comes through to the user. When an alert box pops up, the user will have to click OK to proceed. Syntax: alert ( sometext ); Confirm Box A confirm box is often used if you want the user to verify or accept something. When a confirm box pops up, the user will have to click either OK or Cancel to proceed. If the user clicks OK, the box returns TRUE. If the user clicks Cancel, the box returns FALSE. Syntax: confirm ( sometext ); Prompt Box A prompt box is often used if you want the user to input a value before entering a page. When a prompt box pops up, the user will have to click either OK or Cancel to proceed after entering an input value. If the user clicks OK the box returns the input value. If the user clicks Cancel the box returns NULL. Syntax: prompt ( sometext, default-value ); JavaScript Functions A function contains a code that will be executed by an event or by a call to the function. We may call a function from anywhere within a page. REVISION 9608 SECTION 1 17

18 Functions can be defined both in the <head> and in the <body> section of a document. Syntax:- Function function_name (var1, var2, varx) JavaScript Events Events are the beating heart of any JavaScript application. This gives us an overview of what event handling is, what its problems are and how to write proper cross-browser scripts. Without events there are no scripts. Whenever a user of JavaScript takes action, he causes an event. QUESTION 7 Recognise and identify some PHP code. ANSWER 7 Server-side scripting is a web server technology in which a user s request is fulfilled by running a script directly on the web server to generate dynamic web pages. A common scripting language for server scripting is PHP. Uses of PHP Performs system functions i.e. from files on a system it can create, open, read, write and close them. Can handle forms, i.e. gather data from files, save data to file, through you send data, and return data to the user. Add, delete or modify elements within your database through PHP. It can restrict users to access some pages of any website It can encrypt data. Ways of Sending Information GET method o The GET method sends the encoded user information appended to the page request. The page and the encoded information are separated by the? character. REVISION 9608 SECTION 1 18

19 POST method o The POST method transfers information via HTTP headers. PHP Variables All variables in PHP are denoted with a leading dollar sign $ The value of variable is the value of its most recent assignment Data Types in PHP INTEGERS DOUBLES BOOLEANS NULL STRINGS ARRAYS QUESTION 8 An amusement park has a website. This includes a page where potential visitors can enquire about the price for an individual or group visit. The user can enter the number of people in their group. The admission price will be calculated and displayed. REVISION 9608 SECTION 1 19

20 (a) Give the range of line numbers in the web page script that are JavaScript code. (b) (i) Give the identifiers of two variables which have been used by the programmer. (ii) Give the range of line numbers where selection is performed. (c) Explain the use of the following in JavaScript. (i) the prompt function (ii) the var keyword ANSWER 8 (a) lines 8 15 (b) (i) groupsize groupprice (ii) lines (c) (i) outputs a prompt for user input/prompts the user for input returns an input value (ii) declares a (local) variable REVISION 9608 SECTION 1 20