Typing a URL into a browser feels instant, but behind the scenes a complex sequence of network processes takes place. In IB Computer Science, students are expected to understand this process at a conceptual, step-by-step level, linking together networking, protocols, and servers.
IB examiners reward answers that show logical sequencing, not just a list of buzzwords.
Step 1: URL Is Interpreted by the Browser
When you enter a URL, the browser first:
- Identifies the protocol (usually HTTP or HTTPS)
- Extracts the domain name
- Determines the resource being requested
For example, the browser recognises:
- How the data should be requested
- What type of connection is needed
No data is transferred yet — this is preparation.
Step 2: DNS Lookup
Computers communicate using IP addresses, not domain names.
The browser must:
- Contact a Domain Name System (DNS) server
- Request the IP address associated with the domain name
If the IP address is cached locally, this step is faster.
If not, DNS servers are queried until the correct IP address is found.
This step converts a human-readable name into a machine-usable address.
Step 3: Establishing a Connection
Once the IP address is known, the browser:
- Establishes a connection with the server
- Uses TCP to ensure reliable communication
For secure websites, HTTPS adds:
- Encryption setup
- Certificate verification
This ensures data can be transferred safely.
Step 4: Sending the HTTP Request
The browser then sends an HTTP request to the server.
This request includes:
- The type of request (e.g. GET)
- The resource being requested
- Browser and system information
The request travels across the Internet, passing through routers that forward it toward the destination server.
Step 5: Server Processes the Request
The web server:
- Receives the request
- Locates the requested resource
- Generates a response
This may involve:
- Retrieving files
- Running server-side code
- Accessing databases
The server prepares an HTTP response.
Step 6: Sending the Response Back
The server sends:
- The requested data
- HTTP status information
The response travels back to the browser using the same network infrastructure.
TCP ensures:
- Data arrives in order
- Missing data is retransmitted if needed
Step 7: Browser Renders the Web Page
Once the browser receives the response, it:
- Interprets HTML, CSS, and scripts
- Downloads additional resources if required
- Renders the page visually
This is the first point where the user sees content on screen.
Why This Topic Matters in IB Computer Science
IB exam questions may ask students to:
- Describe the full process
- Explain the role of DNS
- Link protocols to stages
- Justify the use of TCP and HTTP
Structured, step-by-step answers score highest.
Common Student Mistakes
Students often:
- Skip DNS entirely
- Confuse servers and browsers
- Describe steps out of order
- Ignore protocols
Clear sequencing is essential.
Final Thoughts
Typing a URL triggers a coordinated process involving DNS, TCP, HTTP, servers, and browsers. Each step plays a crucial role in delivering content quickly and reliably.
Understanding this process helps IB Computer Science students connect networks, protocols, and real-world system behaviour — exactly what examiners are looking for.
