Packet switching · Routing · TCP

Network Post Office

Split a message into packets, route them, reassemble. Real TCP/IP mechanics.

Every web request you've ever made was chopped into small packets, routed individually through the internet's hop-by-hop network, and reassembled at the destination. The packets can arrive out of order; some can be lost and retransmitted. This demo makes that mechanism visible at a slowed-down pace.

Network Post Office

Send a message through the internet and watch how packets travel

Simulate packet loss

What you just learned

When you send a message online, it gets split into small pieces called packets. Each packet finds its own path through the network. They might arrive in different order, but the receiving computer puts them back together. That's how the internet works — millions of packets finding their way, right now.

What’s happening under the hood

›TCP segments a message into packets (~1500 bytes typical), numbers them, and tracks acknowledgments per packet. Lost packets are retransmitted automatically.
›Each hop (router) reads the destination IP, picks the next hop based on its routing table, forwards. No router knows the full path — only the next step.
›UDP skips TCP's reliability layer for lower latency. Video calls and gaming prefer occasional packet loss over the multi-RTT cost of retransmission.

Dig deeper

Phase 5 · Computer Networking

The concept you just explored is taught with full depth in the formal DURA curriculum.