Topic 3 - Communication Revision 6291686

Sections 3.1 Networks 3.2 Error Detection and Topologies 3.3 The Internet and The WWW 3.4 Client Server Model 3.5 HTML and CSS 7664518

3.1 Networks 6291686

Networks Two or more devices that are connected together Advantages Disadvantages Share printers and devices Increased security risks Allows users to hot desk Managing it is complex Security and backup is central Can be expensive to set up

Types of Network Type Full Name Example LAN Local Area Network School WAN Wide Area Network Company with worldwide offices VPN Virtual Private Network Working from home PAN Personal Area Network Connecting to a Bluetooth headset

Network media connects the devices together in a network Copper Cable Fibre Optic Cable Wireless

Remember you do not have to show the result, just the working out Transmission Speed Size (bits) Network speed (bits) Calculate the transfer speed of a 2KB file over a 5Mbps network connection 2 * 1024 * 8 5 * 1024 * 1024 Remember you do not have to show the result, just the working out

Packets Header Body Footer Length, packet number, destination, origin, protocol This contains the actual data that is being transferred Contains error checking data

Protocols, Addressing & Names TCP/IP Rules on the transfer of data over a network MAC Address Unique address written into the hardware Host Name Human readable label given to a device

3.2 Error Detection and Topologies 6291686

Checksums An algorithm used to check for errors in data transmission It calculates a value based on the number of bits in a packet The value is attached to the packet and the process is repeated at the destination, if they do not match there is an error

Data being transmitted Parity Checking A simple form of error detection A parity bit is added to the end of a string of binary code to indicate whether the number of bits in the string is odd or even Data being transmitted Number of 1s Even Parity Odd Parity 0101010 3 01010101 01010100 0001111 4 00011110 00011111

Topologies The way in which devices are connected together Bus Ring Star Mesh Single main cable Connected in a circle Computers linked to a central computer Each computer connected to each other

Wired & Wireless Connections Wired Connectivity Wireless Connectivity Advantages: Faster than wireless Not easy to intercept data Less chance of interference Advantages: No need for a cable, free to move Allows user to use own device Disadvantages: Expensive to install Requires many cables Disadvantages: Slower than wired Signal interference can occur because of walls Data needs to be encrypted

3.3 The Internet and The WWW 6291686

The Internet Global computer network providing information and communication, consisting of interconnected networks using standard protocols.

IP Addresses Each device that connects to a network is assigned an IP address This identifies a computer on a network

DNS server returns the IP address when a domain name is typed in Domain Name System DNS server returns the IP address when a domain name is typed in

Structure of the Internet Routers are used to connect networks together The large networks they support is known as the connecting backbone of The Internet Switches are used to connect devices together in a network

The World Wide Web This is a collection of documents written in HTML HTML stands for Hypertext Markup Language A web browser allows a user to view and navigate these documents

Webpages, Sites & Servers A single document Website A collection of related documents Web Server A computer that hosts webpages and sites

protocol://domain name/path name of the document URLs Uniquely identifies a webpage protocol://domain name/path name of the document http://bbc.co.uk/news

Web Protocols HTTP Hypertext Transfer Protocol Defines how files are displayed and transmitted in browsers HTTPS Hypertext Transfer Protocol Secure Encrypted version.

3.4 Client Server Model 6291686

Clients & Servers Client Computers that makes a request for something Computers that responds to a request

PHP Dynamic (ever changing) webpages are created using PHP Generates pages from a database Think, for instance, Amazon

Scripting Client Side Scripting Server Side Scripting Processed within the web browser Processed on the web server Often created in JavaScript Often created in PHP Uses more of the users processing power Uses less of the users processing power Less secure More secure

Cookies A small text files stored on your computer when you visit a website Saves information with the aim of speeding up your browsing experience Advertisers can use them to track your habits Can be a security risk on a shared computer

Email Protocols POP3 Downloads messages and removes them from the server once downloaded IMAP Downloads messages and keeps them on the server once downloaded

3.5 HTML and CSS 6291686

Basic structure of a webpage <!DOCTYPE HTML> <html> <head> </head> <body> </body> </html> All of the information about the document is placed in the head section All of the information that can be seen on the screen is placed in the body section

HTML documents are structured using tags HTML Tags HTML documents are structured using tags <title>This is a window title</title> <h1>This is the largest heading</h1> <h6>This is the smallest heading</h6> <p>This is a paragraph</p> <img scr = “images/filename.jog”> inserts an image <a href="http://www.bbc.co.uk">BBC Website</a> external link <a href="page2.html">Click here to go to Page 2</a> internal link <br> adds a line break <hr> add a horizontal rule(line) <ul> <li>This</li> <li>inserts a</li> <li>bulleted list</li> </ul> <ol> <li>This</li> <li>inserts a</li> <li>numbered list</li> </ol>

You may be required to sketch the layout of given HTML Layouts You may be required to sketch the layout of given HTML <!DOCTYPE HTML> <html> <head> <title>Alan Turing</title> </head> <body> <h1>Alan Turing</h1> <img src=”alan.jpg”> <hr> <h2>Welcome</h2> <p>Welcome to the Alan Turing website.</p> </body> </html> Alan Turing Alan Turing Image Welcome Welcome to the Alan Turing website.

CSS Cascading Style Sheets are used to save time and improve consistency They allow you to format multiple webpages at the same time They are usually a separate file that each page is linked to

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