TCP is the standard for reliable networking, but UDP offers more control for specialized applications. UDP itself is unreliable, sending packets without guarantees of delivery or order. Many high-performance systems like games and streaming services opt for UDP because it allows developers to build custom reliability mechanisms. This is achieved through an engineering pattern, not a separate protocol, by adding metadata to UDP packets. Key components include sequence numbers to track packets and acknowledgements to confirm receipt. Retransmission timers initiate resends if packets are lost, while duplicate detection handles redundant packets. Packet ordering mechanisms ensure data arrives in the correct sequence for the application. A sliding window allows for multiple outstanding packets, improving throughput. Connection setup, though not inherent to UDP, can be implemented for session management. Heartbeats are used to verify ongoing connections. Congestion awareness is crucial for respecting network capacity. Ultimately, by combining these engineered components, UDP can be transformed into a dependable transport layer tailored to specific application needs, as seen in protocols like QUIC. Reliability in engineering often arises from multiple simple mechanisms working together, rather than a single complex feature.