connectionless

Connectionless describes a communication model in which each unit of data, typically a datagram, is sent without establishing or maintaining a dedicated end-to-end connection. In a connectionless service, each datagram travels independently from sender to receiver, potentially via different routes, and there is no built-in mechanism to guarantee delivery, ordering, or avoidance of duplicates. Routers and networks do not maintain session state about the communication, and no handshakes are required to begin sending.

In network layers, connectionless operation is common. The Internet Protocol (IP) is connectionless, delivering individual IP packets without a prior handshake. The User Datagram Protocol (UDP) is a connectionless transport protocol built atop IP, offering low overhead and minimal delay but no guaranteed delivery, ordering, or reliability. By contrast, connection-oriented protocols (e.g., TCP) establish a session, provide reliable data transfer, and manage flow and congestion control.

Applications that use connectionless services typically prioritize low latency, bandwidth efficiency, or flexibility over absolute reliability. DNS queries often use UDP; real-time audio/video streaming, online gaming, and some voice services may use UDP with application-layer methods for error handling and sequencing.

Reliability and sequencing can be achieved by higher-layer protocols or application logic, at the cost of additional complexity. Security and integrity are not inherent to the connectionless model; encryption, authentication, and integrity checks may be applied at higher layers (for example, DTLS over UDP, or TLS over TCP).