The Open Systems Interconnection model is the universal 7-layer blueprint for how data moves across a network. Each layer owns one job and talks only to the layers directly above and below it — so a problem, a protocol, or an attack can always be pinned to a specific level.
7 layers · TCP/IP mapping · header decoders · 93-protocol atlas · port reference · attack surface · flashcards
The delivery service. Layer 4 takes your message and chops it into numbered segments, hands them to the network, and — if you're using TCP — guarantees every piece arrives, in order, with nothing missing. It uses port numbers to make sure data reaches the right program (port 443 → your browser's HTTPS, not your email). The alternative, UDP, skips the guarantees for raw speed.
End-to-end delivery of the complete message between processes. Segmentation & reassembly, port-based multiplexing, and (TCP) reliability, ordering, flow & congestion control.
TCP Header — 20 bytes minimum. Reliability lives here. · Hover or tap a field to inspect it.