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CSZone.co.uk
OCR H446 · Component 1 · 1.3.4

The Internet, WWW
& DNS

OCR A Level Computer Science · cszone.co.uk
H446 SpecA Level
Learning Objectives

By the end of this topic you will be able to:

Distinguish between the Internet and the World Wide Web
Explain the role of DNS and how domain name resolution works
Describe the structure of a URL and the role of web browsers
Understand how HTML, HTTP and HTTPS relate to the WWW
Internet vs WWW

Internet vs World Wide Web

The Internet
The physical network infrastructure — the global system of interconnected computer networks using the TCP/IP protocol suite. It includes routers, cables (fibre optic, copper), wireless links and satellites. The internet existed before the Web.
The World Wide Web
An application/service that runs on top of the internet. A collection of web pages (HTML documents) linked by hyperlinks and accessed via URLs using the HTTP/HTTPS protocol. Invented by Tim Berners-Lee in 1989.
Other internet services: email (SMTP/IMAP), FTP (file transfer), DNS, VoIP. These all run on the internet but are not part of the WWW. The internet is the highway; the WWW is one of many services using it.
DNS

Domain Name System (DNS)

DNS is the internet's phonebook — it translates human-readable domain names (e.g. cszone.co.uk) into IP addresses (e.g. 104.21.3.18) that routers can use to route packets.
1. Browser checks cache: has the IP been resolved recently? If yes, use the cached address.
2. Recursive resolver (ISP DNS): your ISP's DNS server queries on your behalf if not cached.
3. Root nameserver: knows which TLD server handles .uk, .com etc. Directs the query.
4. Authoritative nameserver: holds the actual DNS record for the domain. Returns the IP address. The IP is cached by the resolver for future use (TTL — Time To Live).
URLs

URL Structure and Web Browsers

URL breakdown: https://www.cszone.co.uk/lessons/1.1?tab=quiz

Protocol · Domain (resolved by DNS) · Path · Query string
Web Browser Role
Sends HTTP/HTTPS request to the web server
Receives HTML, CSS and JS response
Parses and renders the page (builds DOM)
Executes JavaScript
HTML, HTTP, HTTPS
HTML: defines the structure and content of web pages
HTTP: protocol for transferring web pages (plaintext)
HTTPS: HTTP encrypted with TLS — protects data in transit
Exam Practice
OCR H446 Style · 4 marks
Describe the process that occurs when a user types "www.example.com" into a browser and the IP address is not cached locally.
[4 marks]
1
The browser sends a DNS query to the recursive resolver (usually the ISP's DNS server), asking for the IP address of www.example.com.
1
The recursive resolver queries a root nameserver, which directs it to the .com TLD nameserver.
1
The TLD nameserver directs the resolver to example.com's authoritative nameserver, which returns the IP address.
1
The resolver returns the IP to the browser and caches it for the TTL duration. The browser then sends an HTTP/HTTPS request to that IP to retrieve the web page.
Common Mistakes

Don't Lose Marks

!
Saying the internet and the WWW are the same — the internet is the physical network infrastructure; the WWW is a service (collection of web pages) that runs on top of it. Email, FTP and DNS are also internet services, not part of the WWW.
!
Saying DNS translates URLs — DNS translates domain names (the hostname part: www.cszone.co.uk) to IP addresses. It does not resolve full URLs including paths and query strings — those are handled by the web server after the connection is established.
!
Saying HTTPS is a different protocol from HTTP — HTTPS is HTTP transmitted over a TLS-encrypted connection. The structure and semantics of HTTP remain the same; TLS provides the encryption layer.
1.3.4a Complete
Well done! ✓
The Internet, WWW and DNS
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