Overview

• How to connect to the Internet
  • Internet Service Provider(ISP)
  • Internet (Web) Server
  • Internet Protocol (IP) Address
  • MAC addresses
  • Uniform Resource Locator(URL)
• How to build up a webpage
  • HyperText Mark-up Language (HTML)
• How to transmit data between user and server
  • Hypertext transfer protocol (HTTP)
  • Hypertext Transfer Protocol Secure (HTTPS)
• How to present the website
  • Web browsers

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Connecting to the Internet

Internet Service Provider(ISP)

To connect to the Internet, there must be a company to provide the service. ISPs are the organizations that grant Internet Access to users.

FUNCTIONS

• Provide access to the internet
• Provide user an IP address
• Monitor usage
• Supports domain names
• Provide security service
• Provide web hosting facilities
• Provide online data storage
• Usually charge a monthly fee

Internet (Web) Server

A special computer with special programs constantly switched on and connected to the Internet. It has a IP address like the devices connected to the internet.

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IP address

WHAT IS IT

Every device is  given a unique address, known as the Internet protocol(IP) address, by ISP when connecting to the network.

USAGE

• Identify each device connected to the Internet
• Can be used instead of URL
  For example http://109.108.158.1would take you straight to the device corresponding to this address.

IPV4 V.S. IPV6

According to IPv4, the IP address is a 32-bit number written in dotted decial form: xxx.xxx.xxx.xxx
e.g. 172.16.254.1

However in IPv6, the length of IP address is 128 bit and it’s written in hexademical with the form: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx
e.g. 2001:0DB8:AC10:FE01:: (zeros are ommitted)

STATIC V.S. DYNAMIC

• Static: doesn’t change each time when it is connected to the Internet
• Dynamic: can change each time when a device is connected to the Internet

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MAC address

WHAT IS IT

• A unique value associated with a network adapter on a LAN
• Fixed to the hardware device (NIC: Network Interface Card)

FORMAT

• 12-digit hexadecimal numbers (48 bits in length)
  MM:MM:MM:SS:SS:SS or MM-MM-MM-SS-SS-SS
• First half contains ID of Manufacturer assigned by Internet Standard Body
• Second half contains Serial number assigned to NIC by Manufacturer

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Uniform Resource Locator(URL)

WHAT IS IT

To visit a specific website, we must have its location, which is the URL
e.g. https://www.alevel.com.cn/glevel.pdf

The web browser will break up the URL and present the corresponding content later.

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How to build up a webpage

HyperText Mark-up Language (HTML)

WHAT IS IT

• A language used to create the website
• Used in both structure and presentation
• Uses tags to define colour / font / graphics / layout

STRUCTURE & PRESENTATION

• Similarity
  • Defined using the markup tags
  • Dictate the appearance of the website
• Structure
  • Used for layout
    (Includes the semantics (meaning) and structural mark-up of the document)
• Presentation
  • Used for formatting / style
  • Kept separate form structure – easier to update colour/font
  • Often stored in a file called a CSS
    (The CSS is then linked to the HTML document to implement the presentation requirements)
• Compare – To help you understand, the image below shows a few examples
  

TAGS

HTML tags are element names enclosed by angle brackets.
They usually come in pair.

• The first tag in a pair is the start tag and the second tag is the end tag
• The end tag is written like the start tag, but with a slash inserted before the tag name

Example:

<tr>
    <td><h3>Small car</h3>
    <h3>Used car sales</h3>
    <h2>Cars from $500</h2>
    <br></br><h2>Cash sales only</h2></td><br></br>
</tr> 

Cascading Style Sheets (CSS)

WHAT IS IT

• A presentation language
• Can be included directly in the HTML tags, in the head section of the HTML, or in an entirely separate document (CSS style sheet)

USAGE

• Provide a web browser with styling instructions for the HTML

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How to transmit data between user and server

There’re several protocols, but IGCSE only focus on two: HTTP and HTTPS

Hypertext transfer protocol (HTTP)

• Protocol for data communication on world wide web
• Determines how messages are formatted, transmitted, and the actions web servers and browsers should take in response to commands
• When a user enters an URL in a browser, an HTTP command is sent to the Web server directing it to fetch and transmit the requested Web page

Hypertext transfer protocol Secure (HTTPS)

What’s the meaning of Secure?

• Contain an additional layer of security
• Website is using SSL/TLS
• Data send to and from the web server is encrypted

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How to present the website

Web Browser

WHAT IS IT

• A software which allows a user to display a web page on their computer screen
• Web browser interprest or translates the HTML code from websites and show the result of the translation

HOW DOES IT READ THE URL

The web browser will break the URL into three parts:

• Protocol
• Domain / Web server name
• File name

Example: https://www.alevel.com.cn/glevel.pdf

• https – protocol
• www.alevel.com.cn – Web server
• glevel.pdf – File name