TCP
A reliable transport protocol that guarantees data arrives in order and without errors. It uses a three-way handshake to establish connections.
What is TCP?
A reliable transport protocol that guarantees data arrives in order and without errors. It uses a three-way handshake to establish connections.
TCP is a foundational concept that sits in the Core Fundamentals area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "TCP" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn TCP in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the TCP lessonRelated lessons
Lessons that touch on TCP as part of a larger topic.
TCP Optimization
Tuning TCP parameters and techniques to maximize throughput and minimize latency for cloud workloads
intermediate · cloud infrastructure
Keep-Alive Connections
Reuse TCP connections across multiple requests to eliminate handshake overhead
intermediate · api design protocols
Connection Reuse
Pool and reuse connections across your application to maximize throughput and minimize overhead
intermediate · api design protocols
TCP/IP Stack
The four-layer model that powers every internet connection, from electrical signals to web pages
intermediate · cloud infrastructure
QUIC
The protocol replacing TCP for the modern web, built on UDP with encryption, multiplexing, and zero-RTT built in
intermediate · cloud infrastructure
See also
Related glossary terms you might want to look up next.
HTTP
The protocol powering the web. A request-response model where clients ask for resources and servers respond. Stateless by design.
WebSocket
A protocol for full-duplex communication over a single TCP connection. Unlike HTTP, the server can push data to the client without being asked.
SSL/TLS
Cryptographic protocols that encrypt data in transit between client and server. TLS is the modern successor to SSL. The 'S' in HTTPS.