15.12.5 What Happens When You Type a Website Address into a Browser?
- Why Does It Happen So Quickly?
- What Is a Content Delivery Network?
- Is the Communication Secure?
- How Many Packets Are Involved?
- What Should You Remember?
Short Answer
When you type a website address into a browser and press Enter, a remarkable sequence of events begins. Within a fraction of a second, your computer translates the website name into an Internet Protocol (IP) address, establishes communication with a remote server, exchanges hundreds or even thousands of packets through numerous routers, retrieves the requested information, and displays the completed web page. Although this process involves many different technologies, it is usually so fast that users are completely unaware of the complexity involved.
Step 1: You Enter a Website Address
The process begins when you enter a web address such as www.example.com. This type of address is known as a Uniform Resource Locator (URL).
People find names much easier to remember than numbers, so websites use descriptive names rather than IP addresses. However, routers cannot forward packets using names.
Before communication can begin, the browser must determine the IP address associated with the website.
Step 2: Finding the Website's IP Address
To translate the website name into an IP address, the computer consults the Domain Name System (DNS).
DNS is often described as the Internet's telephone directory. Instead of looking up telephone numbers, DNS looks up IP addresses. For example, a DNS server might determine that: www.example.com corresponds to the IP address 93.184.216.34. Once the browser knows the destination IP address, it can begin communicating with the appropriate web server.
Many computers temporarily store recently used DNS information so that frequently visited websites can be reached even more quickly.
Step 3: Preparing the Information for Transmission
The browser now prepares a request asking the server for the desired web page.
Before transmission, this information passes through several protocol layers. The Transport Layer adds information allowing the receiving computer to deliver the request to the correct application. The Internet Protocol then adds the source and destination IP addresses. Finally, the Data Link Layer places the packet inside a local network frame suitable for the communication technology being used, such as Ethernet or Wi-Fi.
The request is now ready for transmission.
Step 4: Leaving Your Home Network
The first device to receive the packet is usually your home broadband router.
The router examines the destination IP address and determines where the packet should be sent next. The packet is then forwarded to your Internet Service Provider (ISP).
At this point, the packet has left your local network and entered the wider Internet.
Step 5: Travelling Across the Internet
The packet now begins its journey through a series of interconnected networks.
It may travel through:
- metropolitan fibre-optic networks;
- national communication backbones;
- submarine optical cables;
- satellite links;
- microwave radio systems; or
- international Internet exchange points.
Each router along the way performs the same simple task. It examines the destination IP address, consults its routing table, and forwards the packet to the next appropriate router.
Although the packet may pass through many different communication technologies, the IP packet itself remains essentially unchanged throughout the journey.
Step 6: Reaching the Web Server
Eventually the packet reaches the network containing the destination web server.
The final router delivers the packet to the server using the local communication technology operating within that network. The web server receives the request and determines which information has been requested. Depending upon the website, this may involve:
- retrieving stored web pages;
- accessing databases;
- generating dynamic content;
- performing calculations; or
- communicating with other servers.
Modern websites often perform many thousands of operations before sending the first response.
Step 7: Sending the Response
The server now prepares the requested information for transmission.
Rather than sending the entire web page as one enormous block of data, it divides the information into many smaller packets. Each packet is given:
- the server's IP address;
- your computer's IP address; and
- the appropriate transport-layer information.
These packets then begin the return journey across the Internet.
Interestingly, the return path is not necessarily identical to the outward journey.
Different packets may even follow different routes depending upon current network conditions.
Step 8: Reassembling the Web Page
As packets arrive at your computer, the browser reassembles them into their original order.
The browser then interprets the information received. A modern web page often consists of many different components, including:
- HTML documents;
- images;
- style sheets;
- JavaScript programs;
- fonts;
- audio;
- video; and
- advertising or analytics services.
Many of these components are downloaded simultaneously from several different servers.
Only after all the necessary resources have been received can the complete web page be displayed.
Why Does It Happen So Quickly?
The entire process usually takes only a fraction of a second.
Several factors contribute to this impressive performance. These include:
- high-speed optical fibre;
- powerful routers;
- efficient routing protocols;
- local caching of frequently used information;
- modern web browsers;
- cloud computing; and
- Content Delivery Networks (CDNs).
Together, these technologies allow billions of users to access information almost instantaneously.
What Is a Content Delivery Network?
Many popular websites no longer store information in only one location.
Instead, copies of frequently requested material are distributed across numerous servers located around the world. This arrangement is known as a Content Delivery Network (CDN). When you request a web page, the Internet often directs your request to the nearest available server rather than the original source. This reduces communication delay, lowers network congestion, and improves reliability.
It also explains why the same website may appear equally responsive whether accessed from Sydney, London, or New York.
Is the Communication Secure?
Most websites today use Hypertext Transfer Protocol Secure (HTTPS).
HTTPS encrypts the communication between your browser and the web server. Even if someone intercepted the packets while they travelled across the Internet, the information would appear as unintelligible encrypted data. This protection is particularly important for:
- online banking;
- electronic commerce;
- email;
- medical information; and
- business communication.
The small padlock symbol displayed by most web browsers indicates that the connection is encrypted.
How Many Packets Are Involved?
Many people imagine that loading a web page requires only a single message.
In reality, even a relatively simple website may involve hundreds or thousands of packets. Large websites containing images, videos, interactive features, and advertising may require tens of thousands of packets before the page is fully displayed. Each packet is independently routed through the Internet before being reassembled by your computer.
This packet-based approach allows the Internet to use communication resources efficiently while remaining highly reliable.
What Should You Remember?
Loading a web page is one of the best examples of internetworking in action.
A simple action performed by the user triggers a sequence of operations involving DNS, IP addressing, routers, transport protocols, cloud computing, and secure communication. Although these processes involve millions of devices and communication links worldwide, they occur so quickly and reliably that users rarely think about the extraordinary engineering that makes the modern Internet possible.
Every time you press Enter after typing a website address, you are witnessing one of the most remarkable achievements in the history of digital communications.
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