TCP vs UDP: The Transport Layer Protocols Compared
A comprehensive, search-optimized comparison of TCP and UDP transport protocols, three-way handshakes, and use cases.
At-a-Glance Protocol Comparison
Both TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) operate at the Transport Layer (Layer 4) of the OSI model, but their delivery guarantees differ completely:
• TCP: Connection-oriented, reliable, orders data packets, performs flow and congestion control. It guarantees delivery of all packets. • UDP: Connectionless, unreliable, doesn't order packets, and runs with zero flow control. It sends packets as fast as possible ("fire-and-forget").
The TCP Three-Way Handshake
Before transmitting data, TCP establishes a connection via a handshake:
- Client sends SYN (Synchronize) packet.
- Server responds with SYN-ACK (Synchronize-Acknowledge) packet.
- Client returns ACK (Acknowledge) packet.
Connection is now open and data packets can flow reliably.
Selecting the Protocol
• Use TCP for services requiring absolute data completeness: Web browsing (HTTP/HTTPS), Email (SMTP), File transfer (FTP), and REST APIs. • Use UDP for real-time services where speed overrides completeness: Video streaming (VoIP, Zoom), multiplayer gaming (UDP packets representing locations), and DNS resolution.