UDP sends datagrams without TCP’s connection and reliable stream guarantees. Applications choose how to handle loss, duplication and ordering.
Before you start
You should understand clients, servers, IP addresses and ports. Follow a request through name resolution, connection establishment and application exchange. Distinguish protocol guarantees from deployment policy, and use observations from the relevant layer rather than guessing from one browser error message.
The practical goal is to reason through this situation: A real-time application may prefer dropping stale data over waiting for retransmission. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Define acceptable loss
Real-time state may become useless before retransmission finishes.
Step 2: Use message identity
Sequence numbers can reveal duplicates and outdated data.
Step 3: Add only needed reliability
Acknowledgments and retries require bounds and congestion-aware behavior.
Worked scenario
A real-time application may prefer dropping stale data over waiting for retransmission.
A position update for time one arrives after the update for time two. A real-time client may discard the older update rather than apply it and move backward. A financial operation cannot assume the same tolerance; reliability belongs in an explicit application protocol, not the act of sending a datagram.
Common mistake
UDP does not make delivery reliable merely because local sending succeeds.
Verify the behavior
Inject loss, duplicates and reordering and verify the intended application outcome.
Interview exercise
Build a reliable UDP workflow.
Answer and reasoning
Define acknowledgements, retries, identity and ordering only where the application requires them, with congestion awareness.
Continue learning
Compare the scenario with the Networking interview questions and test your understanding with the Networking MCQs. For terminology and implementation details, consult the reference material.