Connectionless service is a service in which no logical connection is set up between sender and receiver before data is transferred — each packet (datagram) carries the full destination address and is routed independently of other packets.

• Packets may follow different paths and arrive out of order; ordering/reassembly is left to higher layers.
• No handshake, no reserved resources → faster, cheaper, and robust, but no guarantee of delivery, ordering or error-free transfer (e.g., IP, UDP).
• Analogous to the postal system: each letter is independently addressed and delivered.
• Contrasted with connection-oriented service, where a connection is established, data follows the same path, and the connection is released (e.g., TCP).