🗓️ Week 01 – Day 03
The Internet and the Web

LSE ME204

Dr Jon Cardoso-Silva

LSE Data Science Institute

12 Jul 2023

The Internet and how it works

We are surrounded by hosts

  • Hosts are devices that can send or receive traffic
  • Host can be anything:
    • laptops
    • smartphones
    • PCs
    • supercomputers
    • etc.

Client-Server model

  • Host interacts and exchanges “messages”.
  • Those hosts that send requests are called clients
  • Those that respond to them with content (webpages, data, emails, etc.) are called servers

Such a request-respond system is called a client-server model

IP addresses

  • Each host needs a unique name to communicate with others
  • In networking this name is called an IP address
  • An IP address weighs 32 bits and hence conveys 32 1-s and 0-s
  • We split those into 4 chunks and get an address of the following format:

The hierarchy

  • IP addresses are assigned hierarchically
  • Each new part of the IP address represents a certain part of the network

UK UK first_layer 44.XX.XX.XX UK->first_layer LSE LSE first_layer->LSE second_layer 44.20.XX.XX LSE->second_layer DSI DSI second_layer->DSI third_layer 44.20.140.XX DSI->third_layer

Networks

  • Hosts are interconnected through a complex set of cables, routers, switches, etc.
  • Each of these networks has its own rules of connectivity
  • Examples of smaller/local networks:
    • your house (laptop + printer + smartphone)
    • LSE (many PCs + laptops + supercomputer)
    • an office (laptops + printers + projectors)
  • If you unite all of the networks
    + add rules of their connectivity
    called protocols you will get the Internet

Protocols

Why do we need protocols?

  • Before around 1973 computers didn’t have a unified system of rules to interact
  • In 1973 the development of the so-called TCP/IP (Transmission Control Protocol + Internet Protocol) has started

  • “that allowed any system to connect to any other system, using any network topology” (Hall 2000)

TCP/IP

  • TCP/IP implies a family of different protocols
  • Each of these protocols serves a certain purpose

The most widely used protocols include:

  • Address Resolution Protocol (ARP)
  • Domain Name System (DNS)
  • File Transfer Protocol (FTP)
  • Internet Message Access Protocol (IMAP)
  • HyperText Transfer Protocol (HTTP)

HTTP example

  • A user sends a request to the server and gets back a webpage.
  • Usually, HTTP protocol is in the form of HTTPS, where S stands for secure.

For example: https://lse.ac.uk

World Wide Web (WWW)

  • When you send an HTTP request to a web server you get back a web page
  • A web page is a document that can be displayed in a web browser
  • We refer to the “World Wide Web” as a collection of web pages that are connected through hyperlinks
  • The World Wide Web is a central part of the Internet, but it’s not the same thing

What’s the future of the Web?

  • You can find links to watch this past event here
  • There’s a link to a recent interview that Sir Tim Berners-Lee gave to Wired here

Tools for creating web-pages

There are 3 key web standards:

  • HTML (HyperText Markup Language) - used to create the “skeleton” of the page
  • CSS (Cascading Style Sheets) - used for advanced styling
  • Java Script - used for interactivity

During the course, you will mostly be working with HTML but will eventually have to interact with CSS, less so with Java Script.

<!DOCTYPE html>
<html>
  <body>

  <h1>My First Heading</h1>
  <p>My first paragraph.</p>

  </body>
</html>

Live Demos

  • How to create HTML pages
  • How to style them
  • Let’s browse W3Schools together
    • it’s a great resource for learning HTML, CSS, and JavaScript

After the ☕ break:

  • Markdown
  • R Markdown
  • Group Exercises (HTML and XML parsing)

References

Hall, Eric A. 2000. Internet Core Protocols: The Definitive Guide. Beijing ; Cambridge, Mass: O’Reilly.