1. Topic 3 - Communication Revision

2. 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

3. 3.1 Networks

4. 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

5. 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

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

7. 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

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

9. 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

10. 3.2 Error Detection and Topologies

11. 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

12. 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 3 4

13. 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

14. 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

15. 3.3 The Internet and The WWW

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

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

18. 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

19. 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

20. 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

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

22. protocol://domain name/path name of the document
URLs
Uniquely identifies a webpage
protocol://domain name/path name of the document

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

24. 3.4 Client Server Model

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

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

27. 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

28. 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

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

30. 3.5 HTML and CSS

31. 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

32. 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=" 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>

33. 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.

34. 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

35. End