TCP vs UDP: Reliable Streams vs Fast Datagrams

Sat, 01 Aug 2026 20:00:00 +0900

Overview

TCP and UDP are the two core transport-layer protocols used to move data between hosts, but they trade reliability for speed in opposite directions. TCP prioritizes reliable delivery through handshakes, acknowledgments, and retransmission, while UDP prioritizes low-latency delivery by sending datagrams with no setup or delivery guarantees. Choosing between them shapes how an application handles packet loss, ordering, and throughput.

Comparison Diagram

Comparison Table

Aspect	TCP	UDP
Connection setup	Three-way handshake (SYN, SYN-ACK, ACK) establishes a stateful connection before any data moves	No handshake — sender transmits datagrams immediately with no prior negotiation
Delivery guarantee	Guaranteed via sequence numbers and acknowledgments; lost segments are detected and resent	Best-effort only; lost packets vanish silently with no notification to either side
Ordering	Segments are reassembled in the original order regardless of arrival sequence	No ordering guarantee; packets are delivered to the application in whatever order they arrive
Flow & congestion control	Dynamic window sizing and congestion-avoidance algorithms throttle the sender to match network capacity	None; the application sends at whatever rate it chooses, independent of network conditions
Error handling	Checksum plus automatic retransmission recovers corrupted or missing segments	Checksum only; corrupted or missing packets are simply dropped, not recovered
Overhead & latency	Larger 20+ byte header and handshake/ACK round trips add processing and latency	Minimal 8-byte header and no round trips keep per-packet overhead and latency low
Connection teardown	Explicit four-way FIN/ACK exchange formally closes the connection on both sides	No connection state exists, so transmission simply stops with nothing to tear down

Key Differences

TCP is connection-oriented, requiring a handshake before data flows, while UDP is connectionless
TCP guarantees reliable delivery through acknowledgments and retransmission; UDP offers none
TCP performs congestion control to avoid overwhelming the network; UDP has no such mechanism
UDP’s minimal header overhead gives it consistently lower latency than TCP
TCP preserves packet ordering end-to-end; UDP delivers packets in whatever order they arrive

When to Use Each

TCP

Udp on IT Comparison

TCP vs UDP: Reliable Streams vs Fast Datagrams

Overview

Comparison Diagram

Comparison Table

Key Differences

When to Use Each