Why is a connectionless protocol deemed unreliable?

A connectionless protocol is deemed unreliable primarily because there is uncertainty about message reception. In connectionless communication, such as that used in UDP (User Datagram Protocol), messages, or packets, are sent without establishing a dedicated end-to-end connection. As a result, there’s no guarantee that the messages will reach their intended destination, nor is there any mechanism for error checking or acknowledgment of receipt. Thus, a sender cannot confirm whether the recipient has received the message, leading to potential issues such as lost or out-of-order packets.

This inherent characteristic distinguishes connectionless protocols from connection-oriented protocols, which establish a connection before data transfer and often include mechanisms to ensure reliable delivery and correct sequencing. The design of connectionless protocols prioritizes speed and efficiency, sacrificing reliability in scenarios where the delivery of each packet is not crucial, such as in live video or voice data.