Internet Packets and Routing

How Data Travels Across Networks

Related Labs

The internet transmits data not as a continuous stream but as discrete packets — small chunks of data with header information including source and destination IP addresses. Large files and web pages are split into many packets that may travel different routes across the network and be reassembled at the destination. This packet-switching architecture was deliberately designed to be resilient: if one router fails, packets are automatically rerouted around the outage.

The TCP/IP protocol suite governs how packets are structured, addressed, routed, and reassembled. IP (Internet Protocol) handles addressing and routing; TCP (Transmission Control Protocol) ensures reliable delivery by numbering packets and requesting retransmission of any that are lost. DNS (Domain Name System) translates human-readable domain names (livephysics.com) into numeric IP addresses that routers can use. Every website request involves multiple layers of protocols working in concert: application (HTTP/HTTPS), transport (TCP/UDP), network (IP), and link (Ethernet/Wi-Fi).

Key Facts

Packets: data split into small labeled chunks; each packet contains source, destination, and sequence info
IP address: unique numeric identifier for each device on the internet (IPv4: 32-bit; IPv6: 128-bit)
Router: a network device that reads packet headers and forwards packets toward the destination
TCP: connection-oriented protocol that guarantees delivery and correct order of packets
UDP: connectionless protocol, faster but no guaranteed delivery (used for video streaming, gaming)
DNS: translates domain names (google.com) to IP addresses; hierarchical distributed database

Vocabulary

Packet: A unit of data transmitted over a network, containing a header with routing information and a payload of actual data.
IP address: A unique numerical label assigned to each device on a network; used by routers to route packets to the correct destination.
Router: A networking device that forwards packets between networks based on IP addresses, choosing optimal paths.
Protocol: A set of rules that defines how data is formatted, transmitted, and received between devices on a network.
DNS (Domain Name System): A distributed system that maps human-readable domain names to IP addresses, acting as the internet's phone book.

Common Mistakes to Avoid

Thinking the internet is centralized. The internet has no single control point — it is a decentralized network of networks. Packet routing adapts automatically to outages.
Confusing TCP and UDP. TCP provides reliable, ordered delivery with error checking (used for web pages, email). UDP is faster with no delivery guarantee (used for live video, DNS queries).
Assuming packets always take the same route. Each packet is routed independently based on current network conditions; packets from the same transfer may take entirely different paths.
Thinking HTTP and HTTPS are the same. HTTPS encrypts the connection using TLS, protecting data in transit. HTTP sends data in plain text and is insecure for sensitive information.

Practice Questions

1 A file is 1 MB and each packet carries 1 KB of data. Approximately how many packets are needed to transmit the file?
2 Explain why a video call might use UDP instead of TCP even though UDP doesn't guarantee delivery.
3 Describe what happens step-by-step when you type 'livephysics.com' into a browser and press Enter, from DNS lookup to page display.