Overview
This lecture explains how data travels across the Internet, describing each stage from your initial request to the final delivery of information to your web browser.
How Data Travels on the Internet
- Clicking a link initiates a flow of information packaged as data packets.
- Each packet contains sender and receiver addresses, type, and sometimes a proxy server address.
- Data is divided into packets of limited size for efficient transport.
Local Area Network (LAN) and Routers
- Packets first travel through the Local Area Network (LAN), connecting devices within one building.
- A router examines packet addresses and forwards them to other networks as needed.
- Router switches are more efficient, quickly routing IP packets to their destinations.
Proxy Servers and Corporate Networks
- Proxy servers act as middlemen, reducing Internet load and providing security.
- The proxy checks web addresses (URLs) in packets and blocks disallowed ones.
- Approved packets are sent onward to the Internet.
Firewalls and Security
- Firewalls protect the internal network by blocking unauthorized external traffic and preventing sensitive data from leaving.
- Only packets meeting firewall criteria can pass; others are blocked.
- Common ports: 80 for web traffic, 25 for email.
The Internet and Packet Routing
- The Internet is a global network of interconnected routers and switches.
- Packets may travel by satellite, phone lines, wireless, or cables, not always by the shortest path.
- If a packet is lost or unacknowledged, it is resent until delivery is confirmed.
Arrival at the Destination Web Server
- At the destination, a firewall again screens incoming packets by port and content.
- The web server receives, opens, and processes the packets, completing the request.
- Response data is packed and sent back through the same network path.
Key Terms & Definitions
- Packet — A small unit of data sent over a network, containing addressing and content information.
- Router — A device that forwards data packets between different networks.
- Proxy Server — An intermediary server used for security and reducing Internet traffic load.
- Firewall — A security system controlling incoming and outgoing network traffic based on rules.
- Port — A numerical channel used for specific types of Internet traffic (e.g., 80 for web).
- LAN (Local Area Network) — A network connecting devices within a limited area like a building.
Action Items / Next Steps
- Review how data packets move through proxies, firewalls, and routers.
- Understand the role of each network device in securing and forwarding Internet traffic.